Sugar and water 'as good as a sports drink', says study

Monday November 30 2015

Some sports drinks contain only glucose

Adding a spoonful of table sugar to a glass of water could be just as good as – or better than – a sports drink, several media outlets have reported. The news comes from a study that compared whether a group of long-distance cyclists performed better when they had a glucose or sucrose mix drink.

Fourteen experienced male cyclists were randomly given a drink of sucrose or glucose stirred into water before and during a three-hour cycling stint.

Both drinks maintained the body's glucose stores, which are broken down to provide energy during physical activity if there's not enough glucose available in the bloodstream. However, British researchers found the cyclists performed better on the sucrose drink.

Many sports drinks designed to provide energy during exercise use sucrose or mixes of glucose and fructose – but many still rely on glucose alone. Sucrose is made up of glucose and fructose, whereas glucose is available in a form ready to be used by the body.  

The researchers suggest glucose-only drinks could produce gut discomfort, and sucrose-based alternatives, or simply sugar in water, could make exercise easier.

While the findings are interesting, this is a small study involving just 14 male endurance cyclists. The results can't inform us of the effects in women, less experienced exercisers, or people performing different types of exercise. Even for male cyclists, a much larger sample may give different results.

This study does inform us about how the body may use sucrose and glucose differently during exercise, but limited firm conclusions can be drawn about the best form of nutrition before, during or after exercise based on its results alone.  

Where did the story come from?

The study was carried out by researchers from the University of Bath, Northumbria University, Newcastle University, and Maastricht University.

It was funded by Sugar Nutrition UK and Suikerstichting Nederland, and was published in the peer-reviewed American Journal of Physiology – Endocrinology and Metabolism.

The news reporting is generally representative of the study's main findings, but would benefit from acknowledging that this research has limited implications because it used such a small, select sample group.

What kind of research was this?

This small randomised crossover trial aimed to compare the effects of glucose and sucrose (table sugar) drinks on the body during endurance exercise. A crossover trial means the participants acted as their own controls, drinking both drinks on two separate occasions.

Carbohydrate – which includes sugar – and fat are the main energy sources used during moderate-intensity endurance exercises. The carbohydrate source comes from glucose in the blood, which is continuously being topped up from the liver by the breakdown of glycogen, the stored form of glucose.

The body's glycogen stores therefore become depleted during exercise, unless carbohydrate is taken in the form of food or drink to provide a fresh source of glucose.

The researchers aimed to better understand the effect that drinking different types of sugary drinks has on the depletion of glycogen stores during exercise.

What did the research involve?

This study involved cyclists who performed endurance exercise while drinking either glucose or sucrose drinks. Researchers compared the cyclists' glycogen stores before and after exercise.

14 healthy endurance cyclists (all male) were involved in the study. They were randomised to either a glucose or sucrose (granulated sugar) drink before an exercise test. One to two weeks later they performed a repeat test after drinking the other drink.

On each occasion, participants arrived at the test centre after fasting for 12 hours and having avoided strenuous exercise for the previous 24 hours. The cyclists' last meal was standardised by the researchers, so they all had the same energy intake.

The carbohydrate test drinks were made up of 108g of either glucose or sucrose mixed with 750ml of water to give a 7% carbohydrate solution. Participants were given 600ml of the drink (86.4g carbohydrate) immediately before exercise, with a further 15ml (21.6g carbohydrate) given every 15 minutes during exercise.

The exercise involved a five-minute warm-up at 100 watts, after which power was increased up to 50% of the individual's peak power output (established during preliminary tests) for the remaining three hours.

A special imaging technique called magnetic resonance spectroscopy (MRS) was used to examine the breakdown of glycogen in liver and muscle tissue before and after exercise.

The researchers took blood samples to look at glucose and lactate levels, as well as expired breath samples to look at oxygen and carbon dioxide levels. They also questioned the participants about abdominal discomfort and how tired they felt during exercise.

Four of the participants also attended on another occasion to perform a control exercise test, where they drank only water.

What were the basic results?

Liver glycogen stores did not decrease significantly after the exercise tests, and did not differ between the two drinks. Muscle glycogen stores did significantly decrease after the tests, but again were not significantly different between the two drinks. Comparatively, both liver and muscle stores declined when only water was consumed during exercise.

Carbohydrate use was estimated by a calculation looking at the difference between the carbon dioxide expired and the oxygen used up during exercise. This was significantly greater with sucrose than glucose, suggesting the sucrose drink was being better used to provide energy.  

Participants also reported their perceived exertion increased to a lesser extent during exercise when they had sucrose compared with glucose. Gut discomfort was also less with the sucrose drink.

How did the researchers interpret the results?

The researchers concluded that, "Both glucose and sucrose ingestion prevent liver glycogen depletion during prolonged endurance exercise".

They say sucrose ingestion does not preserve liver glycogen concentrations any better than glucose, but sucrose does increase whole-body carbohydrate utilisation compared with glucose.

Conclusion

This study aimed to see whether having a sugary drink available during endurance exercise preserves the body's glucose stores in the form of glycogen. They also wanted to see whether there was any difference between sucrose or glucose in terms of performance.

As may be expected, the researchers found drinking both sucrose and glucose drinks during exercise provided an energy source, thereby preserving the body's glycogen stores.

However, the body seemed to make better use of the carbohydrates to provide energy when it was given in the form of sucrose rather than glucose, and participants felt they were getting less exhausted.

The findings suggest both sucrose and glucose are a good energy source during exercise, though plain sugar (sucrose) in water had the slight edge in this study.

These tests involved just 14 male endurance cyclists, which is an important limitation of this study. This means we should take care before applying the results to all groups – for example, women, less experienced sportspeople, or people performing different types of exercise. Even for male cyclists, a much larger sample could have given different results.

There are also many different aspects related to sports nutrition that could be examined, such as the effects of eating food and drink containing different nutrient sources an hour or two before exercise, or the effects of eating after exercise in replenishing energy stores.

Overall, this study informs us about how the body may use sucrose and glucose differently during exercise, but limited firm conclusions can be drawn about the best form of sustenance before, during or after exercise.

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Loneliness 'may affect the immune system'

Tuesday November 24 2015

Humans are an inherently social species

"Being lonely won't just make you miserable; it could also suppress your immune system and knock years of your life," the Daily Mail reports. 

This headline was prompted by a laboratory study in humans and rhesus macaque monkeys, which aimed to investigate if there were biological mechanisms associated with isolation that could also be associated with the risk of chronic disease or early death.

The findings suggest increased activity of the sympathetic nervous system – responsible for the "fight or flight" response – may overstimulate development of inflammatory white blood cells in the bone marrow. At the same time it may decrease the production of antiviral proteins, reducing the body's ability to fight infections.

However, at this stage this is still just a hypothesis. The study has not directly demonstrated that people who are socially isolated are more likely to become ill or die earlier and the immune system played a key role.

Loneliness and social isolation can be complex emotions, and it may be difficult to pin down a single causative factor. It could be a cycle where people with a chronic disease may be less motivated to socialise with others, increasing the sense of isolation, and so on.

Many people in the UK – particularly older adults – can be lonely and socially isolated. But there are ways to combat loneliness, both by seeking help if you are lonely and by helping lonely and isolated people in your community.   

Where did the story come from?

The study was carried out by researchers from the University of California and the University of Chicago, with financial support provided by the US National Institutes of Health.

It was published in the peer-reviewed scientific journal PNAS on an open-access basis, so it is free to read online or download as a PDF.

The UK media's reporting of the research was generally accurate, but could have benefited from making it clearer that we don't know whether these findings provide the whole answer.

Also, although this study looks at a previously observed concept, it hasn't demonstrated that people who are lonely or isolated are more likely to become ill or die earlier.  

What kind of research was this?

This laboratory study in humans and rhesus macaque monkeys aimed to investigate the cellular effects of loneliness. Various studies have already linked social isolation in humans to chronic disease and mortality, though the possible biological mechanism behind this has remained poorly understood.

In humans, feeling socially isolated can involve feeling threatened and being hyperalert. Humans evolved to live in groups with other humans, so prolonged isolation may, on an unconscious level, trigger feelings of profound unease about potential threats: if all of your tribe has suddenly vanished, you could be in a lot of trouble.

Animal models have shown the response to a threat involves signalling from the sympathetic nervous system (SNS) – responsible for the "fight or flight" response – to the bone marrow, where new blood cells are produced.

SNS signalling is thought to increase the activity of "pro-inflammatory" genes, which stimulate the development of early-stage myeloid blood cells in the bone marrow. These myeloid cells give rise to various types of white blood cells (involved in fighting infection), as well as red blood cells and platelets.

It is thought increased myeloid stimulation could contribute to inflammation-related chronic diseases. Meanwhile, while increasing the activity of pro-inflammatory genes, SNS signalling is thought to decrease the activity of genes involved in the production of antiviral immune proteins.

This process is called the conserved transcriptional response to adversity (CTRA) and is associated with specific gene activity, known as CTRA gene expression. This study aimed to find further evidence of the possible links between perceptions of social isolation and sympathetic nervous system effects on the myeloid cells and the CTRA.       

What did the research involve?

The research involved groups of humans and rhesus macaques, and looked at how perceived isolation was associated with measures of immune blood cells and CTRA gene expression.

The human study involved 141 people taking part in the Chicago Health, Aging and Social Relations Study (CHASRS). About a quarter of these people perceived themselves to be highly socially isolated, based on their scores on a loneliness scale during the first five years of the study.

The current research involved blood samples collected from these people during study years 5 to 10. The researchers looked at white blood cell count and CTRA gene expression. Urine samples were also collected to measure the "fight or flight" hormones adrenaline and noradrenaline, and the stress hormone cortisol.

The researchers looked at the association between these biological measures and the score on the loneliness scale, taking account of various potential confounding factors, including age, gender, marital status, income and lifestyle factors.

The macaques were classified to have low, intermediate or high social isolation based on their assessed sociability and behaviours that indicated they felt threatened. Researchers similarly took urine and blood samples from these animals examining stress hormones, white blood cells and gene expression. 

What were the basic results?

The researchers found people with perceived social isolation had an average 6.5% increase in the activity of genes making up the CTRA profile. After additional adjustment for stress, depression and level of social support, isolation was associated with a 12.2% increase in the activity of CTRA genes. Social isolation was also associated with increased levels of white blood cells involved in the inflammatory response.

Similar results were found in macaques – those perceived as socially isolated demonstrated higher CTRA gene activity, with up-regulation of "pro-inflammatory" genes and down-regulation of genes involved in the production of antiviral immune proteins.

This was also demonstrated as an impaired response when the macaques were experimentally infected with simian immunodeficiency virus (SIV), a type of virus that affects primates.

Both humans and macaques with perceived social isolation also demonstrated increased urinary levels of the hormone noradrenaline. 

How did the researchers interpret the results?

The researchers concluded that their study shows socially isolated people have elevated sympathetic nervous system activity, which is associated with activation of the CTRA gene profile.

This is characterised by up-regulation of pro-inflammatory genes and down-regulation of genes involved in the production of antiviral proteins.  

Conclusion

People who are lonely and socially isolated have often been suggested as being at higher risk of illness, disease and early death. This study has aimed to further explore the possible biological mechanisms behind this.

The findings suggest it may involve the "fight or flight" response overstimulating the development of inflammatory white blood cells in the bone marrow, while decreasing the production of antiviral proteins. The idea is this altered immune and inflammatory response could therefore contribute to the increased disease risk.

But this is only a hypothesis. Though the research in animals has suggested socially isolated macaques may be more susceptible to viral infection, this study has not proved that socially isolated humans are more likely to become ill or die earlier.

It also does not confirm this is the only biological mechanism by which social isolation may confer an increased disease risk in humans. Feelings of loneliness and social isolation can be complex emotions that may be influenced by many personal, health and life circumstances.

For example, a person may have a chronic disease that has caused them to become more withdrawn, depressed and socially isolated. This chronic disease may then cause an increased mortality risk, rather than being a direct effect of the social isolation.

As such, there may be several contributing factors involved in a cycle and it can be difficult to pin down a single causative factor – isolation, for example – directly leading to the outcome, such as disease or early death.

However, what is fairly apparent from this and previous research is that, whatever the biological mechanism(s) that may be behind it, loneliness and social isolation do seem to be associated in some way with disease and illness.

If you are feeling isolated and lonely, there are a range of organisations that can help you reconnect with people. Volunteer work can also be an effective way of meeting new people, as well as boosting your self-esteem and wellbeing.

Read more about how to combat feelings of loneliness.

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'Fit for work' disability tests linked to increase in suicides

Tuesday November 17 2015

Suicide is a leading cause of death in middle-aged men

"Fitness to work tests linked to 590 extra suicides in England," warns the Daily Mirror. The paper reports a "horrific death toll" from the policy of reassessing disability benefit claimants. But there is reason to be cautious about whether the suicides were directly linked to Work Capability Assessments (WCAs).

WCAs, introduced in 2010, are intended to assess what work, if any, people are fit to do. People found to be fit for work are moved off disability benefit and expected to look for a job.

Researchers used data about the changing numbers of suicides, reported mental health problems, and prescriptions of antidepressants in 149 local authority areas in England. These were then compared with the numbers of people living in those areas who had undergone WCAs.

The main reported findings were that for every 10,000 WCAs in an area:

• there were an estimated six extra suicides
• there were 2,700 extra cases of reported mental health problems
• GPs prescribed an extra 7,020 antidepressants

It cannot be assumed the WCAs were the direct cause of the increases in mental health problems seen in the study, which only compared rates per area.

This means we do not know whether the people who took their own lives or reported mental health problems had actually been through a WCA. Though, to be fair to the researchers, the government didn't release the data that would make such an analysis possible.

If you are troubled by persistent low mood, contact your GP. If you are thinking about suicide, you should phone Samaritans' free 24-hour helpline on 116 123. 

Where did the story come from?

The study was carried out by researchers from the University of Liverpool and the University of Oxford. It was funded by grants from the National Institute of Health Research, the Commission of the European Communities, and the Wellcome Trust.

The study was published in the peer-reviewed Journal of Epidemiology and Community Health on an open access basis, so it is available to read free online.

The tone of the media coverage differed, as you would expect with a story with such strong political overtones.

The Mail Online reported the study's findings in detail, but gave prominence to the Department for Work and Pensions' (DWP) description of the research as "wholly misleading", while the Daily Mirror used stronger, more emotive language, calling the extra suicides linked to assessments a "horrific death toll" and only including the DWP's statement at the very end of its report.

BBC News, The Guardian and The Independent gave more balanced coverage.

Buzzfeed News was the only news source to make the point that many of the limitations of the study were down to the DWP refusing to release more precise data on people who underwent a WCA.  

What kind of research was this?

This was an observational study, which looked at population-level data over time to see whether changes in rates of Work Capability Assessments (WCAs) were associated with rates of mental health problems. These types of observational studies can find links between factors, but cannot definitively prove that one causes another.  

What did the research involve?

Researchers collected information about mental health outcomes from 149 local authorities in England between 2004 and 2013. They looked to see how this was associated with the numbers of WCAs carried out in the different local authorities between 2010 and 2013. They adjusted their figures to take account of other factors that could have affected mental health outcomes.

The mental health outcomes studied were numbers of suicides – including deaths from injury of undetermined cause, sometimes used by coroners when it is unclear whether someone intended suicide – as well as the number of people reporting mental health problems in surveys and the number of antidepressant prescriptions written by GPs. 

For each outcome, the researchers calculated the rate per 100,000 people, looking only at adults aged 18 to 65 (those of working age who might be affected by WCAs).

Local authorities introduced WCAs at different rates, dependent partly on the number of people in an area receiving disability benefits and the number of staff available to start work. 

The researchers looked at how many people in an area had been through a WCA per 10,000 by the end of each quarter from 2010-13. They used these figures to look for links between WCAs and mental health outcomes.

Because more WCAs were carried out in deprived areas, the researchers adjusted their figures to take account of different deprivation, employment, wages and local authority spending levels, as well as looking at long-term trends in mental health conditions in individual areas.

They carried out a number of checks for other external factors that might influence results (confounders), including looking for links you would not expect to see, such as between WCA rates and mental health problems in adults over 65.

They also looked at whether the number of people with mental health problems increased before or after the number of WCAs in an area rose. All these tests were designed to make the results as reliable as possible.  

What were the basic results?

The study found rates of suicides, mental health problems and prescriptions of antidepressants were higher in areas that carried out more WCAs, after adjusting for baseline differences between areas. 

The researchers estimated for every 10,000 people reassessed, you would expect to see an additional six suicides (95% confidence interval [CI] 2 to 9), an extra 2,700 reports of mental health problems (95% CI 548 to 4,840) and 7,020 extra antidepressants prescriptions (95% CI 3,930 to 10,100).

Between 2010 and 2013 1.03 million people, or 80% of existing disability claimants, were reassessed using the WCA, equivalent to 3,010 per 10,000 of the population. 

During the study period the researchers calculated there were 590 additional suicides (5% of all suicides), 279,000 additional self-reported mental health problems (11% of total), and 725,000 more antidepressants prescribed (0.5% of total).

The extra tests designed to take other factors that might have affected the results into account did not find any evidence other factors were involved. 

How did the researchers interpret the results?

The researchers said this was the first analysis of the effects of the WCA policy on mental health, and the results indicate that, "It may have had substantial adverse consequences".

They say the process is potentially harmful and doctors should consider their involvement in implementing WCAs on ethical grounds.  

Conclusion

It is always hard to assess the direct impact of an intervention, outside the context of a randomised controlled trial. When the intervention is a social policy affecting thousands of people in very different circumstances around the country, the difficulty is that much greater.

The researchers did the best they could to guard against problems such as unexplained factors that might have affected the results, or reverse causality, where what looks like a result of an intervention is actually a cause of it.

Despite this, the study can only demonstrate associations between the data. We cannot say for sure that the WCAs were the direct cause of the mental health outcomes examined.

There is probably no way to tell this, even if you examined every single case of mental illness and suicide to find out whether the individual had been through a WCA and what the impact on them had been.

Mental health is complex, and influenced by various hereditary, health, personal and lifestyle factors. It is rarely possible to identify a single definite cause for suicide.

Population-level studies like this provide the best evidence we are likely to get about the potential effects of social policies, but they cannot provide firm answers.

It is important to keep the results in perspective. While the numbers of extra suicides (590) linked to WCAs sounds like a lot, this is an estimate. The researchers say the figure could be anywhere between 220 and 950, which is quite a wide margin of error. And the numbers who have undergone WCAs is much bigger – well over a million people.

We also cannot ignore the point that for many disabled people, regular employment can be empowering, not a burden. Disability needn't be an obstacle to working – there's a lot of guidance, support and training that can help you get back to work. Read more advice about disability and work.

If you, or someone close to you, is suffering from a mental health problem or thinking about suicide, it's vital to get help right away. There are many sources of support and good treatments for depression and anxiety, which can help people through difficult times.  

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Study calls for smartphones and tablets to have 'bedtime mode'

Monday November 16 2015

Short wavelength blue light may affect melatonin

"Smartphones, tablets and e-readers should have an automatic 'bedtime mode' that stops them disrupting people's sleep," BBC News reports.

The concern is the devices emit short-wavelength blue light, which may disrupt the production of melatonin, a hormone that helps us sleep.

The news comes from a study that examined the short-wavelength blue light emissions produced by three commonly used devices:

• a tablet – iPad Air
• an e-reader – Kindle Paperwhite first generation
• a smartphone – iPhone 5s

Previous research suggested the blue light these devices emit can have a disruptive effect on the sleep hormone melatonin when they are used around bedtime.

This study confirmed the three devices do produce this light, with text producing slightly more intense light levels than the popular Angry Birds game. It also found special orange safety glasses filter out some of the blue light, and a sleep app for children produces less blue light. The researchers suggest the design of future devices and apps could be adapted to limit the colour palate at night.

But this wasn't an experimental study in people. The study didn't examine whether using these devices before sleep had a significant effect on sleep quality and duration.

Still, most sleep specialists stress the importance of good sleep hygiene – adopting a regular pattern in the evening that helps both body and mind wind down and relax ahead of sleep. 

Where did the story come from?

The study was carried out by researchers from Evelina London Children's Hospital sleep medicine department, King's College London and the University of Surrey, and received no sources of external funding.

It was published in the peer-reviewed medical journal Frontiers in Public Health on an open-access basis, so it is free to access online.

The UK media's reporting could have benefited from making it clearer that this research didn't actually prove these devices disrupt sleep.

No people were involved in this study, which only measured the light the devices produce. In particular, it is unclear where the Daily Mail's "extra hour's sleep" suggestion comes from.

Also, The Daily Telegraph's slant towards children may suggest this study involved them. It only examined light from the "Angry Birds" game, which is popular with both children and adults (including, apparently, Prime Minister David Cameron).  

What kind of research was this?

This study examined the short-wavelength blue light emissions produced by a tablet (iPad Air), e-reader (Kindle Paperwhite first generation) and a smartphone (iPhone 5s).

The researchers say there is growing evidence to suggest using light-emitting (LE) devices in the evening may have an adverse effect on sleep quality, duration and daytime performance. Behind the Headlines discussed similar research earlier this year, as well as in 2013.

It is said the brightness, colours and patterns of these devices may influence our body rhythms, particularly when used before bed. Light and brightness during the day has a positive effect on alertness, function and mood, but at night this can impair the production of the sleep hormone melatonin, and so affect sleep.

In particular, short-wavelength blue light is believed to have the most disruptive effect on melatonin. This study aimed to measure the blue light produced by three popular LE devices – a tablet, smartphone and e-reader – allowing comparison by activity type.  

What did the research involve?

The researchers selected the three most popular tablet, smartphone and e-reader devices according to sales data – the iPad Air, iPhone 5s and Kindle Paperwhite first generation, respectively. All of these devices are said to be easily viewed in darkness without additional room lighting ("backlighting").

The tests were therefore carried out in a dark room. Screen brightness for the tablet and smartphone were not altered from automatic settings, but the e-reader was reduced to 50% in accordance with user feedback.

An optical spectrometer – a device that can measure the frequency and wavelength of light – was used to measure light levels while displaying text on all devices, and then the game Angry Birds on the smartphone and tablet.

The researchers also looked at the effect of two devices designed to reduce light disruption:

• blue-blocking, orange-tinted safety glasses
• a sleep diary and behavioural advice app called Kids Sleep Dr, which is designed for evening or night use and uses a "sleep aware" palate of colours that changes the default display settings 

What were the basic results?

The results are fairly complex, listing the spectral distribution of the devices as calculated into equivalent "α-opic" – illuminance of the different photo pigments on the retina of the eye.

Essentially, all the devices showed similar short-wavelength blue light peaks when displaying text (around 445-455nm). The light intensity was slightly lower when showing Angry Birds.

The orange-tinted glasses significantly reduced the intensity of short-wavelength light that got through. The colour palate used in the Kids Sleep Dr app had a different spectral profile and also reduced short-wavelength light emissions. 

How did the researchers interpret the results?

The researchers concluded that all the LE devices they tested produced short-wavelength enriched emissions. They went on to say that, "Since this type of light is likely to cause the most disruption to sleep as it most effectively suppresses melatonin and increases alertness, there needs to be the recognition that at night-time 'brighter and bluer' is not synonymous with 'better'." 

They suggest future software designs are better optimised when night-time use is anticipated, saying devices could have an automatic "bedtime mode" that shifts blue and green light emissions to yellow and red, as well as reduce backlight and light intensity. 

Conclusion

This study measured short-wavelength blue light emissions produced by widely used tablet, smartphone and e-reader devices when displaying text or a game.

The study demonstrates the devices do produce this light, which previous research suggested can have a disruptive effect on the sleep hormone melatonin. The research also found less blue light passes through special orange safety glasses, and a sleep app for children produces less blue light.

Little more can be said about the results of this study. Despite the media headlines, the study does not show these light-emitting devices disrupt our sleep or alter our melatonin levels.

This was not a sleep study where, for example, the researchers measured participants' sleep duration and quality when they did or did not use these devices before sleep.

There are also many other questions readers of these news headlines may have, such as:

• Does it make a difference whether the user is a child or an adult?
• Does it matter what activity I am using the device for? For example, as the emissions from the game are less than text, is this "safe" to use?
• How long do the effects last? What time delay is needed between the last use of the device and trying to go to sleep?
• Does the duration of last use make a difference?
• Is it OK to sleep with the device in the room with me, or do I need to power-off the devices at night?

For a couple of these, the study has leant on previous research and recommendations to give some answers.

The researchers say Harvard Medical School suggests avoiding blue light two to three hours before going to bed, while the National Sleep Foundation suggests turning all electronic devices off at least an hour before bed. The researchers also suggest parents can easily remove devices from the bedrooms of young children or turn them off before they go to bed.

As the researchers rightly acknowledge, sleep duration and quality is rarely influenced by one factor alone. Many personal and environmental factors can contribute to this. Read more advice about methods that can help you, and your family, improve the quality of your sleep.

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'New' sexually transmitted infection 'MG' may be widespread

Friday November 13 2015

The infection can cause bleeding after sex

"A sexually transmitted infection could have infected hundreds of thousands of people in the UK," The Guardian reports. 

The infection – mycoplasma genitalium (MG) – causes few, and often no, symptoms. It is unclear whether it could trigger complications such as infertility.

Many media sources describe MG as a new infection, but it was actually discovered in 1981, although at the time it unclear was if it was a sexually transmitted infection (STI).

New research suggests it could be. A large study of UK adults found that 1 in 100 adults aged 16 to 44 were infected with MG, with the majority showing no symptoms. 

Black men and men from deprived areas were most likely to carry the bacteria, while infection risk increased for those with more sexual partners and those who did not practice safe sex.

MG infection was linked to a higher risk of post-sex vaginal bleeding – a possible sign of disease – but this was tentative, and the only sign that the infection might be causing disease.

This study provides a prevalence estimate and insight into risk factors, but leaves the question of potential long-term harm unanswered. This question requires further investigation using different study types.

However, you can protect yourself from MG and other STIs by practicing safe sex. The humble condom offers the best protection against STIs and can be used during penetrative, oral and anal sex.

Where did the story come from?

The study was carried out by researchers from London-based Universities in England and was funded by the Medical Research Council, the Wellcome Trust, the Economic and Social Research Council, and the Department of Health, with support from an NIHR Academic Clinical Lectureship.

The study was published in the peer-reviewed International Journal of Epidemiology on an open-access basis, so it is free to read online.

Generally, the UK media reported the story accurately. Most UK coverage focused on the possibility that thousands of adults were infected without knowing it – a so-called "stealth STI", as most people don't experience any symptoms.

Some potential harms from MG infection – such as possible female infertility linked to pelvic inflammatory disease – were mentioned in the media, but do not come directly from the study text.

That said, the media coverage usually came with the caveat that the long-term effects of MG infection are largely unknown. 

What kind of research was this?

This was a cross-sectional study looking at whether MG infection was likely to be sexually transmitted, as well as its prevalence in Britain and the risk factors associated with infection.

MG is a bacterium, which evidence identified by the research team says might be linked to genital urinary diseases in men and women, such as post-coital bleeding and urethritis (inflammation of the urethra).

The researchers say there are currently no large population-based epidemiological studies of MG that include prevalence, risk factors, symptoms and co-infection in men and women across a broad age range. Hence, there is doubt about whether it is an STI, how common it is, and uncertainty about whether it causes sexually transmitted diseases (STDs).

Cross-sectional studies are one of the best ways of assessing the prevalence of an infection like MG. However, they are not able to prove cause and effect – that different sexual behaviours increase the risk of MG infection. That said, they can point to highly probable links that can be investigated more robustly in the future using different study designs.

What did the research involve?

Data for this research came from 8,047 respondents to a National Survey of Sexual Attitudes and Lifestyles (Natsal-3) who lived in England, Wales or Scotland from 2010 to 2012.

Participants were interviewed from 2010 to 2012 using computer-assisted face-to-face and self-completion (CASI) questionnaires, which included questions on participants’ sexual lifestyles, history of STIs and current STI symptoms.

Following the interview, a sample of participants was invited to provide a urine sample for testing. The researchers obtained 189 samples from 16 to 17-year-olds who had not been sexually active and 4,507 urine samples from the rest of the 16 to 17-year-olds. They also obtained the same from a sample of 18 to 44-year-olds who reported at least one sexual partner in their lives.

MG infection rates were calculated for 16 to 44-year-olds who reported at least one sexual partner in their lives. They were calculated separately for different age groups and for men and women. Factors linked to MG infection were analysed, such as ethnicity, education level, deprivation levels and sexual behaviours – such as number of sexual partners and unprotected sex in the last year.

What were the basic results?

Just over 1 in 100 men (1.2%, 95% confidence interval (CI) 0.7 to 1.8%) and women (1.3%, 95% CI 0.9 to 1.9%) aged 16 to 44 had an MG infection.

There were no positive MG tests in men aged 16 to 19, and prevalence peaked at 2.1% (1.2 to 3.7%) in men aged 25 to 34 years. By contrast, prevalence was highest in 16 to 19-year-old women, at 2.4% (1.2 to 4.8%), and decreased with age.

The strongest risk factors linked to MG infection were men of Black ethnicity (adjusted odds ratio (AOR) 12.1; 95% CI 3.7 to 39.4) and men living in the most deprived areas (AOR 3.66 95% CI 1.3 to 10.5).

For both men and women, MG was strongly associated with an increased number of total and new partners, and unsafe sex, in the past year. No infections were detected in those reporting no previous sexual experience.

More than 9 out of 10 men (94.4%) and over 5 in 10 women (56.2%) with MG did not report any STI symptoms in the past month.

Women with MG were much more likely to report vaginal bleeding after sex (AOR 5.8; 95% CI 1.4 to 23.3) than those without MG. This, the study authors say, may be a sign the infection is causing disease, but they admit they don't know with any certainty. For example, women with MG were no more likely to report other symptoms that are usually associated with pelvic inflammatory disease, such as pelvic pain, abnormal vaginal discharge or dyspareunia (pain during sexual intercourse).

How did the researchers interpret the results?

The researchers summed up their findings in three key messages:

• "This study strengthens evidence that MG is an STI: there were strong associations with risky sexual behaviours, with behavioural risk factors similar to those in other known STIs, and no infections were detected in those reporting no previous sexual experience.
• Given the uncertainty on the natural history and clinical implications of infection, especially in women, we report that although asymptomatic infection was common, we found a strong association with post-coital bleeding in women. Therefore, in addition to MG being an STI, it can also be an STD.
• MG was identified in over 1% of the population aged 16-44, and among men was most prevalent in 25 to 34-year-olds, who would not be included in STI prevention measures aimed at young people."

Conclusion

This British population study found that around 1 in 100 men and women aged 16-44 living in England, Wales and Scotland are infected with MG, and that it is likely to be transmitted by sexual contact.

The STI doesn't lead to symptoms in the vast majority of men and around half of women. The study wasn't able to tell if the infection was causing disease, but there were tentative signs that it might. For example, more women with MG infection reported vaginal bleeding after sex than those without MG – a possible, but by no means strong, sign the infection may be causing disease.

The overall prevalence masked interesting variation by age, ethnicity and gender. For example, male prevalence of MG was highest in those aged 25 to 34, at 2.1%, whereas in women it peaked earlier in those aged 16 to 19 years, 2.4%.

There are a number of potential biases in this study – for example, non-participation bias to the survey, and bias from non-provision of the urine sample. In each case, the groups taking part might be different to those who chose not to – potentially influencing the results. While this remains a possibility, the authors were aware of the risk and took measures to minimise the influences. For example, the statistical analysis took account of some factors and the team compared the background of the participants taking part with those of the wider population. 

This showed that the group who participated in the study were similar to the British population at large, at least in terms of ethnicity, marital status and self-reported general health.

The study team suggest they may have underestimated MG prevalence in women, as the urine test they used is less effective than an alternative, using vaginal swabs.

To summarise, the study was based on a large number of people living in Britain – over 4,000 urine samples and interviews – so can be considered relatively reliable and applicable to the UK population.

We don't routinely screen for MG infection in adults in Britain, so this study might spark debate about whether we should. To better inform that debate, we need more information about the possible disease-causing effects of the infection: is it harmless, or does it do lasting damage that needs treatment to stop or prevent it? At the moment, we don't seem to have a clear idea.

Even if we don't know the long-term effects of MG infection, it is simple to minimise your personal risk. Ways to prevent MG infection are likely to be the same as for other STIs, such as using condoms during oral, anal and regular sex.

Read more about safe sex and reducing your risk of STIs. 

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Stronger legs linked to stronger brains in older women

Wednesday November 11 2015

Leg strength is an indicator of overall fitness

"Strong legs 'help the brain resist the effects of ageing','' the Mail Online reports. A study that tracked 324 female twins (162 sets) over 10 years found an association between leg strength and cognitive ability, measured through memory testing and brain scans.

The study recruited twins aged 43 to 73 in 1999 and measured their physical fitness using a piece of gym equipment, similar to an exercise bike, to measure the power in their thigh muscles. The women also performed memory tests and completed questionnaires on their usual physical activity level, current health, and lifestyle factors.

After 10 years, they completed another set of memory tests. Some of the twins were also given MRI brain scans to check for changes in the structure in the brain associated with cognitive decline.

The study found women with stronger leg extension had less age-related change in brain function and structure 10 years later, after taking into account their age, lifestyle and other risk factors.

While this is an interesting finding, it is not possible to say less physical strength caused the brain to decline or vice versa. Women with a more active brain may have been more likely to take part in physical exercise.

That said, the study is further evidence of the numerous benefits of physical activity, especially in older women, who may experience weakening of the bones as a result of the effects of the menopause.

Read more about the importance of bone health. 

Where did the story come from?

The study was carried out by researchers from King's College London and was funded by the Wellcome Trust and the National Institute for Health Research (NIHR). There were no reported conflicts of interest.

It was published in the peer-reviewed medical journal Gerontology on an open access basis, so it is available for free online.

The UK media reported on the study both accurately and responsibly. However, some of the study's limitations were not highlighted.

The BBC quoted the director of research at the Alzheimer's Society, Dr Doug Brown, who said that although "the findings added to the growing evidence that physical activity could help look after the brain as well as the body … we have yet to see if the improvements in memory tests actually translate into a reduced risk of dementia". 

What kind of research was this?

This was a cohort study that aimed to assess if muscle fitness (measured by leg power) could predict cognitive change in healthy females over a period of 10 years. It also assessed if leg power was predictive of differences in brain structure and function after 12 years of follow-up in identical twins.

Twin studies like this are useful as they can take into account shared genetic and environmental factors. However, as the study design is observational in nature, we cannot draw firm conclusions on the causality as more than one factor may be responsible for the observed outcomes.  

What did the research involve?

This study included 324 female twins from the UK. The study participants were selected from the TwinsUK volunteer registry, which was originally set up to study ageing in women.

The participants' muscular fitness was estimated based on the strength of the leg extensor muscles (thigh muscles) in 1999. This was done by a trained research nurse using the Leg Extensor Power Rig machine. The machine, similar to an exercise bike, measures leg explosive power by measuring the force and velocity a participant uses when they push down on a pedal.

Participants sat on this machine with their legs slightly bent. The activity leg was then placed on a pedal and they were asked to push the pedal as fast and hard as possible to full extension, "as if performing an emergency stop in a car".

Other measurements and tests included:

• grip strength and lung function
• weight and height
• blood pressure
• blood sugar and cholesterol

Participants were then asked to fill in a questionnaire, which included:

• rating their physical activity during the last 12 months as inactive, light, moderate or heavy
• occupation and income
• smoking and alcohol use
• vegetable intake
• saturated fat intake
• history of ischaemic heart disease
• history of diabetes
• history of mental health conditions

To estimate age-related cognitive changes, study participants underwent a computerised test (CANTAB) once in 1999 and again in 2009. This test is particularly known to be sensitive to age, and measures memory and processing speed of the brain. 

Twenty pairs of identical twins underwent MRI brain scans 12 years after the start of the study. The scans were used to look at the amount of grey matter (tissue made up of nerve cells) in two regions of the brain associated with cognitive ability: the medial temporal lobe and the middle frontal gyrus. 

What were the basic results?

After adjusting for age, lifestyle and psychological factors, both physical activity and leg extensor power had statistically significant protective effects on age-related cognition over a period of 10 years.

Overall, twins who were stronger at the beginning of the study had significantly less deterioration in cognition than their weaker sisters.

The brain scans of identical twins found those with stronger leg extensor power at the beginning of the study had more total grey matter 12 years later than those with weaker power.  

How did the researchers interpret the results?

Researchers concluded by saying the study "found that greater muscular fitness – as measured by leg power – is associated with improved cognitive ageing over the subsequent 10 years in non-impaired community living women". 

Conclusion

This study of 324 female twins from the UK found a positive association between leg extensor power and age-related cognitive activity.

As it was a cohort study, it is not possible to say that increased muscular strength prevented decline in mental ability, as other related or unrelated factors could have played a part.

That said, the researchers did try to account for many of these factors, such as:

• using twins to reduce potential genetic and early environmental confounding factors
• taking baseline cardiovascular risk factor profiles, as these are risk factors for dementia
• taking into account age and sociodemographic details

The finding that women with stronger legs had more grey matter on the MRI scans should also be interpreted with caution. The MRI scans were only taken at one time point, so we do not know whether the amount of grey matter had changed over the course of the study. Additionally, they were only performed on a small subset of 20 identical twins.

Other limitations of the study include:

• At baseline, data on the participant's physical activity level in the previous 12 months was obtained through self-reported questionnaire, and this may have introduced recall bias. There was no follow-up information regarding physical activity levels, which is likely to change over time.
• Researchers have accounted for some of the common confounding factors, but there may be other factors not considered in this study that might have had an influence on the observed outcome.
• None of the study participants are reported to have developed dementia, so it is unclear whether the same results would be found for women at higher risk.

Regardless of these limitations, the beneficial impacts of daily physical activity are well known. 

Find out the government guidelines for physical activity for your age group.

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Is a brisk walk better for losing weight than going to the gym?

Wednesday November 4 2015

A brisk walk should leave you slightly out of breath

"A brisk 30-minute walk five days a week is more effective than any other form of exercise for keeping weight down," The Times reports. That is the reported conclusion of two researchers who looked at data from the annual English Health Surveys from 1999 to 2012.

As expected, they found people who regularly walk briskly for half an hour five days a week were likely to have a lower body mass index (BMI) than people who are less active.

The study found women and those over the age of 50 were most likely to have a lower weight if they walked regularly. By walking, the researchers mean brisk walking that raises your heart rate and makes you sweat slightly, not a gentle stroll.

Walking was also linked to having a smaller waist size – although, for men, sport and other forms of exercise were more strongly linked to waist size than walking. Sport and exercise were also linked to a lower BMI, although the link was not as strong as it was for walking.

However, this study does not seem to have compared the effects of the two types of activity directly, so we cannot say for sure – as many in the UK media have done – that walking is more effective than other types of exercise.

Walking does have the obvious advantage of being free, as well as being an activity you can easily fit into your day-to-day life. Read more about walking for health and how the 10,000 steps a day challenge can help boost your fitness levels.  

Where did the story come from?

The study was carried out by researchers from the London School of Economics and the University of Queensland, and was funded by the Nuffield Trust. It was published in the peer-reviewed journal Risk Analysis.

Many UK media outlets covered the story. Most fell into the trap of assuming walking caused weight loss and, because the link was stronger for walking than for sport or exercise, walking was therefore better for losing weight.

However, the two types of activity were not directly compared, and on some of the analyses in the study, sport and exercise came out better, especially for men.  

What kind of research was this?

This cross-sectional study used data collected at different time points from the annual Health Surveys for England between 1999 and 2012.

This data is compiled by the Health and Social Care Information Centre (HSCIC), the same organisation that operates Behind the Headlines and the rest of the NHS Choices website.

Cross-sectional studies can look at the links between factors, but cannot say whether one factor caused another, or vice versa.  

What did the research involve?

Researchers took data from seven separate years of the Health Survey for England to see what people said about how often they took part in specific activities. They compared this with people's recorded BMI and waist circumference. They wanted to find out whether people's weight and waist size could be predicted by how often they did specific types of physical activity.

The study is not clear about how many people were included in the analysis, although the researchers say they had more than 68,000 "observations" about the types of activity people did.

It's possible this means they used data from 68,000 people, although we can't be sure of this. The figures for BMI and waist measurements were based on 26,878 and 38,836 observations respectively.

The researchers put the data through a number of statistical models to work out the relationship between BMI and waist size and any type of physical activity, then looked specifically at brisk walking, heavy manual work, heavy housework, and sport or exercise, including gym workouts, cycling and running.

They adjusted their figures to take account of confounding factors, including people's age, gender, household size, marital status, ethnic background, where they lived, their level of education and employment.

Finally, they calculated the difference in BMI and waist circumference between people who regularly do each activity for more than 30 minutes five days a week (in line with UK government guidelines) and people not getting this kind of exercise.  

What were the basic results?

The first result, not surprisingly, was people who did the most activity, of any type, had the lowest BMIs and the lowest waist measurements. These effects were strongest in women and people over the age of 50.

Brisk walking was linked to the biggest difference in BMI for both men and women. The researchers found men who regularly walked briskly for more than 30 minutes five days a week had a BMI on average one unit less than those who did not, while for women the difference was 1.8 units.

The equivalent amount of sport and exercise was also linked to BMI, but the difference was smaller. Heavy manual work also showed a link, as did heavy housework for women, but not men.

The effect on waist measurement was similar, with one important difference: women who regularly walked briskly had a waist 4.3cm smaller than women who did not. The researchers say this was the biggest difference for any type of activity for women.

However, for men, sport and exercise had a stronger link to waist measurement than walking. Men who regularly took part in sport or exercise had a waist 3.3cm smaller than those who did not.  

How did the researchers interpret the results?

The researchers said: "The results suggest that those who do five days of any of these physical activities every week for a month could decrease their waist circumference on average by 4.3cm for women and 3.6cm for men."

This is a surprising claim, as the study did not show a change in waist circumference over time, or establish that exercise caused a drop in waist size.

They went on to say: "Overall, we find that brisk walking has the highest association with these measures of weight, with sports/exercise being the runner up in this regard." 

They admitted: "We cannot interpret our findings here as causal," but they called for a public health campaign to encourage walking as an "easy policy option" to combat the obesity epidemic.  

Conclusion

Walking has long been advocated as a good way to keep fit. It is easy to fit into everyday activities, doesn't need special equipment, and most people can do it.

This study shows people who regularly took brisk walks for at least half an hour five days a week – fast enough to get you out of breath and sweat slightly – were likely to have a lower BMI and smaller waist size than other people.

The results don't mean other types of exercise, such as swimming, cycling, playing sport or going to the gym, are worthless. People who regularly did these activities were also likely to have a lower BMI and waist circumference.

The study does not seem to have directly compared the effect of sport and exercise versus brisk walking. We don't know whether the differences in BMI the researchers found would have stood up as statistically significant in a head to head comparison.

It is interesting that men who did regular sport or exercise had a lower waist measurement than men who walked instead. Waist measurement is important as it shows how much fat you carry around vital organs, which has been linked to heart attacks.

It may be that exercise and sport are less strongly linked to BMI than walking because men who work out gain muscle, which weighs more than fat, so will result in a higher BMI.

The main limitation of the study is it cannot prove people's weight is a result of their activity levels. We know diet is also important in determining weight, as well as other factors such as genetic make-up.

It is possible people are more likely to walk or take part in sport and exercise if they have a lower BMI as slimmer people find physical activity easier and more comfortable. We cannot tell whether the people in this study with a higher BMI would have lost weight by walking or exercising more regularly.

However, this study does add to the evidence that walking is a healthy form of exercise linked to keeping to a healthy weight, especially for women and in later life.

The key to sticking to a fitness and exercise plan is to find an activity you enjoy, whether it's walking, running, swimming, cycling, or even rock climbing.  

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Growing up with a dog 'reduces childhood asthma risk'

Tuesday November 3 2015

Exposure to animals may protect against allergies

"Children who grow up with a pet dog in the family home have a lower risk of developing asthma," The Times reports. 

A large Swedish study found an association between pet ownership and reduced risk of asthma. Living on a farm was also found to reduce this risk.

The study found exposure to dogs reduced the risk of both preschool (by 10%) and school-age children having asthma by 13%. And living on a farm as a child – not just visiting one – also appeared to reduce asthma risk by an estimated 31% for preschool children and 52% for school-age children.

Some commentators have argued these results add weight to what is known as the hygiene hypothesis. This is the idea that children who grow up in sterile environments have reduced exposure to infectious agents, such as those carried by dogs, so they have an underdeveloped immune system. This may then make them more vulnerable to allergic conditions such as asthma.

However, one of this study's limitations is the findings can only highlight a potential link: it cannot categorically prove living with or around animals reduces the risk of childhood asthma.

The research has attempted to adjust for various potential confounders, including parental asthma, but other factors may still have had an influence.

One proven way to reduce the risk of childhood asthma is to never expose your children to tobacco smoke (secondhand smoke) both during pregnancy and when they are growing up.

Where did the story come from?

The study was carried out by researchers from Uppsala University in Sweden.

It was funded by the Swedish Research Council, Stockholm County Council, the Strategic Research Program in Epidemiology at Karolinska Institutet, and the Swedish Heart Lung Foundation. There were no significant conflicts of interest.

The study was published in the peer-reviewed JAMA Pediatrics.

The UK media has generally reported the findings accurately. The Independent quoted one of the authors of the study, who said: "These kinds of epidemiological studies look for associations in large populations, but do not provide answers on whether and how animals could protect children from developing asthma.

"We know that children with established allergy to cats or dogs should avoid them, but our results also indicate that children who grow up with dogs have reduced risks of asthma later in life."

What kind of research was this?

This cohort study aimed to investigate the association between exposure to dogs and farm animals during the first year of life – as in living with or around them – and having asthma as a preschool (around three years old) or school-age child (around six years old).

This study design is able to suggest links for further investigation, but is unable to prove cause and effect. There may be a number of other factors influencing risk, such as parental asthma, other allergies, air pollution, or other environmental exposures.

The only way to establish a causal link would be to run a randomised controlled trial (RCT), but realistically such a trial would be both expensive and impracticable – it would be difficult to convince thousands of families to adopt a dog at random or move to a farm, for example. 

What did the research involve?

The researchers included all children born in Sweden over a 10-year period from 2001-10, who were identified through the Swedish Register of the Total Population and the Medical Birth Register.

The need for informed consent and parental permission was waived by the regional ethical board in Stockholm.

The study population was split into two groups:

• children born between January 1 2001 and December 31 2004 (school-age children)
• children born between July 1 2005 and December 31 2010 (preschool-age children)

Children were excluded if their parents moved to Sweden after the child was 15 years of age or if there was incomplete information on parental identity or migration.

For school-age children, their asthma status was assessed during the seventh year of life. For preschoolers, this was assessed from the age of one and then throughout the study period.

Four different asthma definitions were explored:

• an asthma diagnosis obtained only from the National Patient Register (NPR)
• asthma medications noted in the Swedish Prescribed Drug Register (SPDR)
• having both the NPR diagnosis and asthma medications noted in the SPDR
• having either one or both NPR diagnosis and asthma medications noted in the SPDR

The researchers selected having either one or both NPR diagnosis and asthma medications noted in the SPDR as the most appropriate outcome measure.

Exposure to dogs was defined as having a parent registered as a dog owner during the child's whole first year of life. Exposure to farm animals was defined as parents who were animal producers and related workers in the child's first year of life.

A number of statistical analyses were performed to assess different levels of exposure to dogs and farm animals. The analyses were adjusted for potential confounders, including parental age, educational level, country of birth, and asthma status.  

What were the basic results?

During the 10-year study period, there were 1,011,051 children born in Sweden. Researchers included 376,638 preschool-age children, of whom 53,460 (14.2%) were exposed to dogs and 1,729 (0.5%) were exposed to farm animals. They included 276,298 school-age children, where 22,629 (8.2%) of whom were exposed to dogs and 958 (0.3%) were exposed to farm animals.

After controlling for potential confounders, having a dog during the first year of life was associated with a decreased risk of asthma:

When analysed by parental asthma status, school-age children had a reduced risk regardless of whether their parent had asthma or not. However, when dividing up preschool children, exposure to dogs no longer had any effect on asthma risk, either for those with parental asthma or without.

Living with or around farm animals was also associated with a reduced risk of asthma in both school-age children (OR 0.48, 95% CI 0.31 to 0.76) and preschool-age children (HR 0.69, 95% CI 0.56 to 0.84) after adjusting for confounders. 

However, again, the results changed when divided by parental asthma status. For both school-age and preschool children, those who had a parent free from asthma had a reduced risk, but those with a parent with asthma did not.

Dog or farm animal exposure had no significant effect on risk of asthma in children under the age of three.  

How did the researchers interpret the results?

The researchers concluded that: "The data support the hypothesis that exposure to dogs and farm animals during the first year of life reduces the risk of asthma in children at age six years.

"This information might be helpful in decision making for families and physicians on the appropriateness and timing of early animal exposure." 

Conclusion

This cohort study aimed to study the association between living with or around dogs or farm animals during the first year of life and the risk of asthma in preschool children and school-aged children. The results suggest early exposure to dogs and farm animals may reduce the risk of childhood asthma.

However, there are a number of limitations and caveats to consider. This study type can suggest an association, but it cannot prove cause and effect. The researchers adjusted their analysis for various potential confounders, including parental age, education level and country of birth. But it was not possible to account for all confounding factors, and other factors could have had an influence.

Importantly, the researchers did take parental asthma status into account, but adjusting for this gave inconsistent results, with some links remaining significant, while others did not. For example, school-age children with early dog exposure had a reduced risk regardless of whether their parent had asthma.

But when the two groups were divided in two according to parental asthma status, no risk reduction was found for either. When it came to farm animal exposure, risk was reduced in children of parents without asthma, but not in those who had parental asthma, for both groups.

This slightly clouds the picture and makes it difficult to give a clear, consistent message on whether animal exposure has a direct effect on risk, or whether it is influenced by other factors, such as parental or child eczema, hay fever, or dust mite or animal fur allergies. These things may influence both the decision to live with an animal and the child's risk of developing asthma.

That said, the study has strengths: it included a large sample, followed participants for a number of years, and also used medical registers to identify child asthma, rather than relying on parental report.

However, as the researchers used official registers, there may be a problem with missing data for dog ownership or parental asthma status, for example. The study was also unable to account for exposure to other animals, particularly at close family members' homes, where there may be high levels of exposure that would not have been linked.

It is not exactly clear what causes asthma, although it is thought to be a combination of factors, including genetic and environmental. Modern hygiene standards are often considered to be one of these factors, and the researchers suggest this may be why exposure to animals could have a protective effect.

However, this cannot be confirmed at this stage. More research is needed before we can consider giving any official advice to parents about the benefits – or otherwise – of having a pet.  

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