The Telegraph
London, UK
6 March, 2007
This could be your dream diet
According to new research, there might be an easy way to keep trim... stay in bed. Roger Highfield reports on evidence linking obesity with sleep deprivation
The discovery is enough to make you lose sleep: evidence is emerging of a link between a drop in the time society spends slumbering and the dramatic rise in obesity and associated diseases, such as diabetes and high blood pressure.
A flurry of worldwide research has established an intriguing connection between poor sleep and fat stomachs. This has a range of fascinating implications. Levels of obesity could be significantly cut by having a lie-in. Earlier bedtimes and later waking times could be an important, low-cost way to shrink waistlines. And children, in particular, could benefit.
One study featuring 18,000 adults participating in the US Government's National Health and Nutrition Examination Survey throughout the Eighties revealed a surprisingly strong link between waistlines and snoozing. Those who got fewer than four hours of sleep a night were 73 per cent more likely to be obese than those who got the recommended seven to nine hours. Those who averaged five hours had a 50 per cent greater risk, while those who got six hours had a 23 per cent greater risk.
"Maybe, there's a window of opportunity for helping people sleep more, and maybe that would help their weight," said Steven Heymsfield of Columbia University and St Luke's-Roosevelt Hospital in New York, who did the work with James Gangwisch at Columbia. A subsequent study by the same team also linked lack of sleep with high blood pressure.
The implications for children were revealed by a team at Northwestern University, Illinois, which studied 1,400 children aged from three to 12 over a five-year period. "Children who slept more weighed less and were less likely to be overweight five years later," said team member Emily Snell.
This chimed with an analysis from the Avon Longitudinal Study of Parents And Children in the Nineties which, after tracking 13,000 British children as they grew up, concluded that poor sleep at 30 months predicts obesity at the age of seven years. "Earlier bedtimes, later wake times and later school start times could be an important and relatively low-cost strategy to help reduce childhood weight problems," says Snell. "We found even an hour of sleep makes a big difference."
Such studies have helped to convince Snell and others that reduced sleep causes weight problems not the reverse.
The sleep-weight link initially perplexed researchers. More time awake should mean more calories burnt. But people also eat when they're awake, and the effect of chronic sleep deprivation on the brain's food-seeking circuitry is what seems to be influencing obesity as well as raising the risk of insulin resistance, diabetes and heart disease.
One clue may lie in a type of brain cell found while studying narcolepsy, a condition marked by sudden bouts of deep sleep. These cells control our feeding and sleep circuits with the aid of chemicals called orexins. A lack of orexins makes people fall asleep, the right amount ensures both normal sleep and appetite.
Researchers have also found that not enough sleep causes changes in hormones that regulate appetite. Dr Shahrad Taheri from Bristol University, and colleagues in the University of Wisconsin and Stanford in America, examined the role of two hormones, leptin and ghrelin, in more than 1,000 volunteers under "real-life" conditions. Low levels of leptin and high levels of ghrelin will make you feel hungry.
Dr Taheri said: "We found that people who slept for shorter durations have reduced leptin and elevated ghrelin. Individuals who spent fewer than eight hours sleeping were shown to have a greater likelihood of being heavier." People who habitually slept for five hours were found to have 15 per cent more ghrelin than those who slept for eight hours. Complementing this was a 15 per cent fall in leptin. The bleary-eyed also seem to crave carbohydrate-rich foods.
Most recently, a molecular clue came from a study at the Scripps Research Institute in La Jolla, California by Manuel Sanchez-Alavez and Prof Tamas Bartfai, who were interested in the EP3 receptor, one of four types of molecular switches that respond to a type of hormone, called prostaglandin E2 (PGE2).
The Scripps team was studying mice that lack the EP3 receptor protein - and do not develop fevers - when they made a startling discovery: the mice were putting on lots of weight when they were four to five months old. It turned out that the mice without the EP3 protein were more active during the light hours -"night time" for mice, which are nocturnal - and, more importantly, were eating. The increased activity led to more energy expenditure but this did not burn enough of the extra calories and so these mice weighed 15 to 30 per cent more than normal mice.
The research to date chimes with the warning of many chronobiologists that our Stone Age bodies are not suited to today's 24/7 lifestyle. There is evidence that we have reduced the amount of time we spend asleep by up to two hours a night because of increasing pressures on our time, whether from work, school, family, television, computer games or the internet, said Dr Taheri.
He added that it is telling that between 1960 and 2000, the prevalence of obesity doubled in the population while the average number of hours slept per night was reduced. During the same period, the percentage of young adults who slept fewer than seven hours rose from 16 per cent to 37 per cent. Meanwhile, strenuous outdoors activity that helps us get a good night's sleep has declined.
To find out whether a prescription of more sleep can help fight flab, Giovanni Cizza at the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, Maryland, is recruiting 150 tired, obese people who sleep for six hours per night or less for a study. Some of them will be taught how to raise their sleep to seven-and-a-half hours so Cizza can test whether the extra sleep has an effect on weight, body fat, and leptin and ghrelin levels.
Even if the effects of shut-eye are not yet fully understood, and even if they only have a relatively small influence on body weight, they merit more study. Such is the scale of the obesity epidemic that if a simple measure such as encouraging children to sleep for a little longer has a measurable effect, this may be a potent new weapon in the fight against flab.
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