Too little sleep may explain soaring levels of obesity in children, according to a scientist from Bristol University.

Dr Shahrad Taheri, whose research involves the influence of sleep on hormones, says that children spend too little time asleep and pay the price in increased obesity.

Computers, mobile phones, TVs and other gadgets should all be banned from children’s bedrooms to enable them to get a good night’s sleep, he asserts in Archives of Disease in Childhood.

Even two or three nights of shortened sleep can have quite significant effects, he says, disrupting the normal hormonal balance and making more likely a series of long-term consequences, including obesity, diabetes, and heart disease.

Dr Taheri does not claim that poor sleep is the only cause of obesity, but he says that its effects should be taken seriously, on the basis both of experiments and epidemiological evidence.

One study, from the Avon Children of the 90s project, showed that short sleep duration at the age of 30 months predicted obesity at seven years of age.

And many population studies have linked reduced hours of sleep with excess body weight and other metabolic disturbances. Dr Takeri cites 13 such studies in his review.

He admits that these links could be spurious, if there is another factor that causes both poor sleep and overweight. But biological evidence points to a real connection.

Two hormones, leptin and ghrelin, that control appetite have been shown to be affected by sleep disturbances in experiments at the University of Wisconsin.

Leptin is a hormone released by fat cells to tell the brain that fat stores are adequate, and ghrelin, released by the stomach, is a signal of hunger.

In people with too little sleep, the Wisconsin team have found that leptin levels were low, and ghrelin levels high. Both these would encourage an individual to eat more.

The most obvious reason why children sleeping badly would get fat is that by day they would be tired and inactive. Even a small drop in activity can mean that calories consumed exceed calories expended, leading to weight gain.

The process could feed on itself, he suggests. Lots of physical activity means that people sleep better: a lack of it means they sleep less well. So as the sleep debt accumulates and daytime activity falters, sleep suffers yet more, creating a vicious cycle.

There is relatively little data on whether people are sleeping fewer hours than they used to but what data is available suggest that they are. "Sleep duration has declined particularly at the same time as the rise in obesity" he writes.

Other studies have linked TV viewing to obesity, the general assumption being that people who spend a lot of time slumped in front of a TV set are too inactive.

But most TV viewing by children is carried out close to their bedtimes, which could mean that its effect is indirect and caused by disrupting sleep rather than by displacing more energetic daytime activities.

Dr Taheri makes a series of recommendations, aimed mainly at children and adolescents. These include:

• A regular bedtime routine
• Strict bed and wake times
• A quiet, dark and relaxing bedroom
• A comfortable bed that is not used for other activities such as reading, watching TV or listening to music
• No TVs, computers, or other gadgets in the bedroom
• Engaging in physical activity, but not too close to bedtime
• No large meals close to bedtime.

  For adolescents, he suggests allowing them to sleep in at weekends, but not for more than two to three hours, as that can disrupt the normal rhythms.

  They should also avoid bright light at night, and welcome it in the morning, to reinforce the wake-sleep cycle.

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