Could more sleep really be the secret to effective weight loss? Convincing research has shown that just one more hour of sleep a night could help you shed kilos.

In fact, neuro-scientist Karine Spiegel, of France's INSERM, a public organisation dedicated to biological, medical and public health research, claimed that there are more than 30 surveys carried out on worldwide population samples to back up this theory.

"More sleep could be the ideal way of stabilising weight or slimming," she said, and added that, although poor eating habits and a lack of exercise contribute to the global rise in obesity, there is a growing consensus that a lack of sleep also plays a pivotal role.

Sleepless nights up obesity risk

"Around 30 surveys conducted on wide population samples in seven countries have underlined a link between lack of sleep and excess weight or obesity in both children and adults," Spiegel said.

One of the first studies conducted in this field, focused primarily on the problem in children and teenagers, and was carried out in France in 1992.

According to Spiegel, the increase in obesity in the US in the second half of the 20th century corresponded with a mounting decrease in sleep. She put this down to two key hormones produced at night which help regulate appetite - grehlin and leptin - as the culprits.

Less sleep makes you hungry

"Grehlin makes people hungry, slows metabolism and decreases the body's ability to burn body fat, and leptin, a protein hormone produced by fatty tissue, regulates fat storage.

"We have shown that less sleep, i.e. less than four hours a night, caused an 18 percent loss of appetite-cutting leptin and a 28 percent increase of appetite-causing grehlin," she said.

Spiegel stated that these hormonal changes made people hungry for foods heavy in fats and sugars such as chips, biscuits, cakes and peanuts.

Shockingly, the sleep loss caused a 23-24 percent increase in hunger, translating into an extra 350 to 500 kilocalories a day, which Spiegel pointed out "for a young sedentary adult of normal weight could lead to a major amount of added weight”.

However, at this stage it was still unclear whether several years of sleep deprivation could cause lasting harm to the body's ability to restore a balance between the two hormones.

Too much sleep is also bad

In another study, lead by Dr Angelo Tremblay, of Laval University in Quebec City it was found that while too little sleep (less than seven hours) led to weight gain, too much sleep (more than nine hours) also led to weight gain.

In their study, the researchers attempted to gain an understanding of the sleep duration-weight gain relationship. They followed 276 men and women for six years and noted that during that time, people who averaged five to six hours sleep a night gained 1.98 kg more than those who slept seven to eight hours. Conversely, those who slept for nine to 10 hours gained 1.58 kg more than the average-length sleepers.

The study also showed that both short and long sleepers exhibited greater gains in fat mass and waist circumference than average-length sleepers, and were significantly more likely to gain five kg or more. They also were at increased risk of becoming obese.

Tremblay's suggests that too much or too little sleep disrupts appetite control by causing a reduction in leptin. At the same time increasing secretions of grehlin echoes Spiegel's conclusion that too little sleep can make you hungry.

Sleepless childhood has repercussions

But in a second study conducted this year in the US it was found that children who did not get enough shut-eye also faced a greater risk of becoming obese than those kids who got a good night's sleep.

In this case the researchers, from the Johns Hopkins Bloomberg School of Public Health carried out an analysis of epidemiological studies which showed that each extra hour of sleep can cut a child's risk of becoming overweight or obese by up to a whopping nine percent.

On the other hand, the studies showed that children who had the least sleep had a shocking 92 percent higher chance of being overweight or obese than children who slept enough.

"Our analysis shows a clear association between sleep duration and the risk for overweight or obesity in children. The risk declined with more sleep," said Youfa Wang, a senior author of the study, published in the journal Obesity.

"Desirable sleep behaviour may be an important low cost means for preventing childhood obesity and should be considered in future intervention studies," Wang added.

How much is too much or too little?

So how much sleep should your children be getting in order for them to grow up into healthy adults with normal weight?

After researchers reviewed 17 published studies on sleep duration and childhood obesity, they found that most research recommends that children under five years old sleep 11 hours or more, children aged between five and 10 years old get 10 or more hours and children older than 10 get a minimum of nine hours.

With regard to adult sleep patterns, the US National Sleep Foundation found that more than 70 percent of adults over the age of 18 get fewer than eight hours of sleep a night on weekdays and 40 percent get fewer than seven hours.

Among older adults, those between 55 and 84, 13 percent sleep less than six hours a night during the week, while 11 percent have a similar sleep pattern on weekends.

So how much is too little? Researchers concur that the battle of the bulge may ultimately best be waged beneath the sheets for at least seven to eight hours a night.

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