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NHS Direct Health News

NHS Choices: Behind the headlines   + / -  
last updated: Sat, 25 Oct 2014 15:11:01 GMT

 Fri, 24 Oct 2014 10:52:00 GMT 'Putting clocks forward boosts kids' exercise'

“Moving the clocks forward by one extra hour all year in the UK could lead to children getting more exercise every day, say researchers,” reports BBC News.

In the UK, the clocks move forward one hour during the summer months so that there are more daylight hours in the evening (daylight saving time).

A new study has found that children are more active in daylight saving time, regardless of the weather conditions. Its findings suggest that if the clocks were moved forward by one additional hour all year round it could lead to each child in England spending an average of 1.7 extra minutes in moderate to vigorous physical activity per day.

While small, the extra exercise isn’t trivial because children only engaged in this level of activity for 33 minutes a day. Also, spread across the whole population, the impact could be considerable.

However, the study couldn’t eliminate the possibility that there are other things responsible for the associations seen.

The estimates of how much children’s activity would increase would only hold true if the only reason they aren’t more active normally is daylight. Although the researchers took into account the weather in their analyses, it is difficult to adjust for expected (rather than actual) weather conditions. For example, school sports days tend to occur in the summer, in the hope that it will be warm and dry.

 

Where did the story come from?

The study was carried out by researchers from the London School of Hygiene and Tropical Medicine, the University of Bristol and Bristol Biomedical Research Unit, and the International Children’s Accelerometry Database Collaborators. The International Children’s Accelerometry Database is funded by the UK National Prevention Research Initiative. The researchers were funded by the National Institute of Health Research.

The study was published in the peer-reviewed International Journal of Behavioural Nutrition and Physical Activity. This article was open access, meaning it can be accessed for free.

The results of the research were well reported by the BBC and The Daily Telegraph.

 

What kind of research was this?

This was an observational study looking at the relationship between daylight in the evenings and the amount of activity children undertook. Researchers used information from the International Children’s Accelerometry Database, which contains activity data from children participating in studies worldwide, collected using motion sensors called accelerometers. These sensors are worn on the waist, and objectively measure physical activity levels without needing to rely on people remembering and reporting how active they were.

The researchers wanted to assess whether:

  • more evening daylight is associated with higher total physical activity, even after taking into account the weather conditions
  • the overall differences in physical activity in different times of the year are greatest in the late afternoon and early evening
  • changing the clocks affects activity levels

As with all observational studies, it is not possible to prove without a doubt that changing the clocks is directly responsible for the differences in activity levels seen, as other factors could be contributing. However, given that it would not be feasible to test the effect of changing the hours of daylight in a randomised controlled trial, this is the only way of assessing the potential link.

 

What did the research involve?

The researchers examined accelerometer data from 23,188 children aged between five and 16 in nine different countries. They looked to see whether physical activity varied according to time of sunset.

They then examined accelerometer data from the 439 children who had data from a school day just before and just after a clock change (within a week).

The researchers adjusted their analyses to take into account differences in weather (amount of rain or snow, humidity, wind speed and temperature), and differences in the characteristics of the children (such as age, sex and weight).

 

What were the basic results?

Longer evening daylight was associated with a small increase in children’s daily physical activity, even after taking into account other factors. When sunset was at 9pm or later, children spent approximately six minutes longer in moderate to vigorous physical activity than when sunset was at 5pm or earlier. The average time spent performing moderate to vigorous physical activity was 33 minutes per day, so a six-minute difference is not as trivial as it may seem.

The differences in physical activity were greatest in the late afternoon and early evening. The researchers found no association between activity levels in the morning and hour of sunset, and generally no association for activity in the early afternoon. This supported the argument that the extra hours of evening daylight were directly causing the increase in activity seen.

These associations were also seen when comparing the same child just before and just after the clocks changed.

The associations between hour of sunset and more physical activity were only consistently observed in children from five mainland European, four English and two Australian samples. The link was not consistently seen in American, Madeiran and Brazilian samples.

In the English studies, each additional hour of evening daylight was associated with 1.7 extra minutes of moderate to vigorous physical activity per day.

 

How did the researchers interpret the results?

The researchers concluded that in Europe and Australia, more evening daylight appears to increase children’s physical activity. They say that although the average increase is small in terms of minutes per extra hour per child, these small increases would add up when applied across all children in a population.

Also, the increase “compares relatively favourably” with the typical increases in physical activity that can be achieved with intensive programmes aimed at getting children and adolescents to be more active. They conclude that “the introduction of additional daylight saving measures could yield worthwhile public health benefits”.

 

Conclusion

The current study has found that more evening daylight is associated with increased physical activity in children, even after taking into account the weather. The results suggest that if the clocks were moved forward by one additional hour all year round, it could lead to children in England getting an estimated 1.7 extra minutes of moderate to vigorous physical activity per day.

Although this seems like a small amount, it is not trivial in relation to the average amount of activity children were found to have in a day (33 minutes). If every child in the country has a small increase in activity, this adds up to a considerable total increase.

The study’s strengths include the large total number of children assessed, the fact that they used an objective measure of activity, and that the children came from a range of countries.

There are some limitations to the findings of this study. The data was mainly cross-sectional, and it is difficult to eliminate the possibility that there are other things responsible for the associations seen. The estimates of how much activity could increase with a clock change assumes that the differences seen in activity were completely due to the extra hour of daylight. The researchers also note that although they adjusted for the actual weather, it is difficult to adjust for expected weather conditions. For example, school sports days tend to occur in the summer in the hope that it will be warm and dry.

Given that a randomised controlled trial to assess the impact of a clock change would not be feasible, this type of study is likely to be the only way to look at how daylight hours affect activity. The rising levels of sedentary lifestyles and obesity worldwide mean that finding ways to increase physical activity is an important policy area. While this study will contribute to the debate about whether the clocks should go forward an extra hour, there are likely to be a range of other factors the government will consider in making a decision – such as potential business and economic impacts.

 

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Links To The Headlines

Time for change? Moving clocks forward would boost children's health through increased exercise. The Mirror, October 23 2014

Clock change 'good for child health'. The Guardian, October 23 2014

Later sunsets 'increase children's activity levels'. BBC News, October 23 2014

Change clocks to tackle childhood obesity: Shifting time forward by an hour would increase amount of time young can spend playing outside. Mail Online, October 23 2014

Links To Science

Goodman A, et al. Daylight saving time as a potential public health intervention: an observational study of evening daylight and objectively-measured physical activity among 23,000 children from 9 countries. International Journal of Behavioural Nutrition and Physical Activity. Published 23 October 2014

 Fri, 24 Oct 2014 10:29:00 GMT Sunshine isn't slimming and can't halt diabetes

"Sunshine can make you thin," claims the Daily Mirror, while the Daily Express splashed on its front page that, "Sunlight is key to fighting diabetes". Both are strong contenders for the title of the day's most inaccurate health headline.

The news – reported more circumspectly by The Times and BBC News – is based on highly artificial laboratory experiments on mice.

The study found that long-term ultraviolet (UV) light exposure stopped male mice fed a high-fat diet gaining weight. UV also reduced glucose intolerance and insulin resistance and levels of insulin in the blood after fasting, as well as glucose and cholesterol.

In humans, these are signs associated with metabolic syndrome – a combination of diabetes, high blood pressure and obesity that puts you at greater risk of heart disease.

Human skin produces vitamin D when it is exposed to UV light, so the researchers tested whether the same benefits were seen if the mice were given a vitamin D supplement in their food.

But this did not produce the same effects. The researchers instead think nitric oxide, which is also produced when skin is exposed to UV light, may be responsible for the effects of UV.

Mice are nocturnal animals covered in fur, so their skin is not usually exposed to much sunlight. This means this research has no immediate implications for people.

 

Where did the story come from?

The study was carried out by researchers from the University of Western Australia, the University of Southampton and the University of Edinburgh.

It was funded by the BrightSpark Foundation and the Telethon Kids Institute.

The study was published in the peer-reviewed medical journal Diabetes.

The results of this study were well reported by BBC News and The Times, but the same cannot be said for the Mirror and Express.

An extremely kind critic might put the Mirror's claim that "Sunshine can make you thin" and the Express' claim that "Sunlight is key to fighting diabetes" down to wishful thinking and youthful high spirits.

Despite the headline, the Express did manage to rustle up comment from an independent expert from Diabetes UK, something the Mirror failed to do.

 

What kind of research was this?

This was an animal study. It looked at whether UV radiation and taking vitamin D affected the development of obesity and type 2 diabetes in mice eating a high-fat diet.

As the BBC reports, further research is required to see if sunshine has the same effect in people. Mice are nocturnal animals covered in fur, so their skin is not usually exposed to much sunlight.

 

What did the research involve?

The researchers fed 432 male mice either a low-fat diet containing added vitamin D, or a low-fat diet without added vitamin D, for four weeks.

This was done so the mice who had vitamin D supplementation would definitely have enough vitamin D and the mice on the standard diet would have a vitamin D deficiency.

The mice were continued on these diets, and some were switched from a diet low in fat to a diet high in fat. This meant there were four groups of mice:

  • low-fat diet 
  • low-fat diet plus vitamin D
  • high-fat diet
  • high-fat diet plus vitamin D

In each group, mice further split into three groups, which either received no UV radiation or UV radiation at two different doses on a shaved patch on their backs.

One was a low dose that wasn't enough to make the skin go red and was given twice a week. The other dose was enough to make the skin go red and was given once a fortnight.

The mice were fed these diets and irradiated with these UV radiation doses for 12 weeks.

The researchers monitored:

  • the mice's weight
  • their glucose and insulin tolerance 
  • their blood levels of vitamin D, cholesterol, triglycerides (fats), glucose and insulin, and certain hormones (leptin and adiponectin) and signalling molecules

 

What were the basic results?

A high-fat diet significantly increased vitamin D levels in mice fed diets not specifically supplemented with vitamin D.

Mice fed either diet that was further supplemented with vitamin D had significantly higher vitamin D levels than those mice fed a diet that was not supplemented with vitamin D, although the effect of a high-fat diet and vitamin D supplementation was not additive.

UV exposure significantly increased vitamin D levels in mice fed the low-fat diet without vitamin D supplementation, but had no effect on vitamin D levels in mice fed the other diets.

Weight gain 

Mice put on weight during the study. Long-term UV radiation at both doses significantly reduced weight gain in mice fed the high-fat diet without vitamin D supplementation.

Weight gain was similar between the mice that hadn't been irradiated and were fed the high-fat diet without supplementation, and mice fed the high-fat diet with vitamin D supplementation.

Similar results were seen for mice fed the low-fat diet.

Glucose intolerance and insulin resistance

Mice fed the high-fat diet developed glucose intolerance and insulin resistance. However, if mice were also given long-term UV irradiation, they showed reduced glucose intolerance and insulin resistance.

Glucose intolerance and insulin resistance were similar between un-irradiated mice fed the high-fat diet without supplementation and mice fed the high-fat diet with vitamin D supplementation.

Glucose intolerance was also significantly suppressed by long-term, low-dose UV radiation in mice fed the high-fat diet with added vitamin D.

Fasting glucose and insulin levels were also reduced by UV treatment in mice fed the high-fat diet without extra vitamin D.

Cholesterol

Levels of high-density lipoproteins, low-density lipoproteins and total cholesterol were also suppressed by the higher dose of UV irradiation in mice fed the high-fat diet that was not supplemented with vitamin D.

The researchers found vitamin D supplementation reduces the effect UV had on weight gain and markers of metabolic syndrome.

They did further experiments to determine how UV radiation might be having its effect. Their results suggest UV radiation of the skin causes the production of nitric oxide, and this might cause the effects seen.

 

How did the researchers interpret the results?

The researchers conclude that, "Long-term skin exposure to low-dose (suberythemal) and high-dose (erythemal) [UV radiation] suppresses the development of obesity and measures of [metabolic syndrome] in mice fed a high-fat diet. Vitamin D supplementation alone did not reproduce these effects.

"In addition, the suppressive effects of [UV radiation] on obesity and [metabolic syndrome] development were not observed to the same degree in mice that were further supplemented with vitamin D."

 

Conclusion

This study on mice has found long-term ultraviolet (UV) irradiation significantly suppressed weight gain and markers of metabolic syndrome, including glucose intolerance and insulin resistance, and blood levels of fasting insulin, glucose and cholesterol, in male mice fed a high-fat diet.

Many of the benefits of UV radiation were not reproduced by vitamin D supplementation alone. The researchers instead think that another chemical called nitric oxide, which is also produced when skin is exposed to UV light, may be responsible for the differences seen.

Mice are nocturnal animals covered in fur whose skin is not usually exposed to much sunlight. As the BBC reports, further research is required to see if sunshine has the same effect in people.

We can pretty confidently sat that the Express' front page splash saying, "Sunlight is key to fighting diabetes", and the Mirror's claim that "Sunshine can make you thin", are both nonsense. 

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Links To The Headlines

'Sunshine can slow weight gain and diabetes symptoms'. BBC News, 24 October 2014

Sunlight is key to fighting childhood obesity and diabetes, Scots scientists reveal. Daily Express, 24 October 2014

Sunbathing can stop you gaining weight (well, it works for mice). The Times, 24 October 2014

Links To Science

Geldenhuys S, et al. Ultraviolet Radiation Suppresses Obesity and Symptoms of Metabolic Syndrome Independently of Vitamin D in Mice Fed a High-Fat Diet. Diabetes. 2014;63:3759-3769

 Thu, 23 Oct 2014 11:30:00 GMT No need for nightshift workers to avoid steak

"Shift workers should avoid tucking into steak, brown rice or green veg at night," because these foods "disrupt the body clock," the Mail Online reports.

But the research in question involved lab mice who were fed different amounts of dietary iron for six weeks to see what effect this had on the daily regulation of glucose production in their livers.

The research found mice fed lower-iron diets tended to have better regulated glucose production pathways than those on the higher iron diets. The mice did not have disturbed sleep patterns.

In a press release, the researchers raised the possibility their findings could have "broad implications" for people who do shift work, which could increase their risk of type 2 diabetes. This speculation has been mistakenly highlighted by the media.

The results suggest sustained high iron intakes may compromise our glucose regulation in the liver, but we should interpret these results with caution. The results do not prove that high iron intake has any effect on the risk of type 2 diabetes, as diabetes outcomes were not examined.

If you are concerned about diabetes, there are steps you can take to reduce your risk, such as maintaining a healthy weight (which is recommended whatever hours you work).

 

Where did the story come from?

The study was carried out by researchers from the University of Utah in the US and was funded by the Research Service of the Department of Veterans Affairs and the National Institutes of Health.

It was published in the peer-reviewed medical journal, Diabetes.

By taking the press release at face value, the Mail Online has overextrapolated the implications of this research, which has looked at how different dietary iron intakes in mice influence the daily regulation of glucose production in the liver.

This study is not related to shift work – subheadings such as, "for people who work night shifts, it puts the liver's clock out of sync", are not supported by the evidence.

The press department of the University of Utah appears to have misrepresented and overinterpreted the study in the hopes of hitting the headlines. While they have been successful in getting in the papers, they have perhaps done the science a disservice.

In this study, all mice were kept on a 12-hour light/dark cycle. All that was altering was their iron intake, not their sleep/wake patterns.

 

What kind of research was this?

This was an animal study investigating the role that dietary iron has on the circadian (daily) rhythm of glucose metabolism in the liver.

The researchers describe how the liver maintains a daily balance in regulating glucose, and point out that disruption of this rhythm is associated with type 2 diabetes.

Dietary intake is one of the factors that influence the biological clock in our bodies, but little is said to be known about the role of specific dietary components.

This research focused on dietary iron, as iron is an essential component of several proteins in the body concerned with electron transport and metabolism. Also, haem, the chemical compound containing iron, is necessary for the formation of several proteins involved in regulatory pathways.

 

What did the research involve?

In this study, researchers fed mice chow with different iron concentrations. They did this to create iron levels in the body tissues that would be within the range produced by a normal human diet.

Three-month-old male mice were fed on diets containing low (35mg/kg), medium (500mg/kg) or high (2g/kg) amounts of iron. The upper 2g/kg level is said to be within the fourfold range of iron seen in human livers. The mice were fed on these diets for six weeks while they were maintained in a 12-hour light/dark cycle.

After between six and eight weeks on these diets, the researchers also tested the effect of giving the mice three different chemicals in their daily drinking water.

These chemicals either increased haem synthesis, inhibited haem synthesis, or acted as an antioxidant. They gave the mice these chemicals so they could work out how dietary iron was affecting glucose production in the liver.

The mice were then given various tests, including glucose tolerance tests (GTT) and a variation on the GTT: the pyruvate tolerance test (pyruvate is one of the molecules involved in the production of glucose).

The mice also had their blood levels of haemoglobin, red blood cell volume, insulin and glucagon (the hormone produced when blood glucose levels are low) measured. After death, the mouse liver was analysed in the laboratory.

 

What were the basic results?

The researchers found dietary intake influences the daily rhythm of glucose production in the liver.

Mice fed the lower-iron diet had higher blood glucose levels in response to pyruvate injection than mice on the higher iron diets. This result suggests their livers had better regulated glucose production pathways than those who had been on the higher iron diets.

The researchers found haem production varied with dietary iron intake, and haem influences the activity of an enzyme (Rev-Erbα) key to regulating the liver's daily rhythm. This Rev-Erbα enzyme regulates many aspects of glucose metabolism.

To confirm that dietary iron was affecting haem production, the researchers looked at the effect of chemicals that either increased haem levels or blocked haem production. Treatment with either chemical caused the differences in blood glucose regulation seen to disappear.

The researchers thought dietary iron may cause changes in haem synthesis through reactive oxygen species. This is because the protein that regulates the production of one of the enzymes involved in haem synthesis is regulated by reactive oxygen species, and iron creates reactive oxygen species.

Reactive oxygen species are molecules containing oxygen. Depending on the specific context in which they are formed, reactive oxygen species can be both helpful and harmful to the cells of the body.

To test the above hypothesis, mice were fed an antioxidant to mop up reactive oxygen species. This resulted in many of the differences seen between mice fed different diets to disappear.

Iron intake had no effect on haemoglobin concentration or red blood cell volume.

 

How did the researchers interpret the results?

The researchers say their findings demonstrate that dietary iron affects the circadian rhythm and glucose production in the liver by modifying haem levels in the liver.

 

Conclusion

This animal research demonstrates how dietary iron intake affects the daily regulation of glucose production in the liver. Mice fed lower-iron diets tended to have better regulated glucose production pathways than those who had been on the higher iron diets.

This happens because iron intake influences the production of the iron compound haem, which in turn influences the activity of an enzyme involved in regulating glucose production in the liver.

Overall, it is difficult to draw any meaningful conclusions from these findings. The researchers suggest sustained high iron intakes may compromise our glucose regulation in the liver, but interpretations from this research should be made with caution. The results from this mouse study do not prove that a high iron intake increases the risk of type 2 diabetes.

The results certainly do not have any immediate implications for shift workers. This leap seems to have been made because the study looked at daily rhythms of glucose production, but all mice in this study were maintained on the same light/dark cycle – only their iron intake was altered.

The most effective method of reducing your diabetes risk is to achieve and then maintain a healthy weight. If you are struggling to get the weight off, why not try the NHS weight loss plan, a free evidence-based diet and exercise plan designed to deliver sustainable weight loss. 

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Links To The Headlines

Why shift workers should avoid tucking into steak, brown rice or green veg at night: Iron-rich foods 'disrupt the body clock'. Mail Online, October 22 2014

Links To Science

Simcox JA, Mitchell TC, Gao Y, et al. Dietary Iron Controls Circadian Hepatic Glucose Metabolism through Heme Synthesis. Diabetes. Published online October 14 2014


 

 
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