Those who wake up early ... get fat! A new study reveals that children who don't sleep enough are more prone to grow obese when adults. It appears that less sleep impedes the body from synthesizing enough amounts of a hormone that inhibits the appetite.

The Australian researchers at the University of Queensland in Brisbane investigating young children from birth to 21 found those who had sleeping impairments were almost two times more likely to be obese as young adults than those with a healthy sleep.

The study made on 2,500 children showed that poor sleep quality in childhood was a major risk factor for obesity in early adulthood, no matter their lifestyle or diet. While just 13 % of those who rarely experienced irregular sleeping at two and four were obese, those with regular sleeping problems had this number increased to 23 %.

The scientists put this on a lower release of the appetite suppressant leptin and higher amounts of levels of the appetite stimulant ghrelin. Less sleep could also affect the metabolism and shift body's reactivity to insulin, which determines the rhythm at which the body puts on fat.

"There were three possible reasons why children who struggled to sleep might grow fatter. First, children who sleep less have more time in which to eat. Second, lack of sleep results in tiredness and less physical activity during the day, causing less energy expenditure than energy intake. Or less physical activity may result in reduced sleep quality or duration." said lead researcher Dr Abdullah Al Mamun.

"As well as affecting the hormones regulating-appetite, reduced sleep could also mean that lower levels of the growth hormone somatotrophin were released."

This hormone is involved in the degradation of the fatty tissue. If further investigations confirm these results, a new significant cause of the world's obesity has been detected.

Previous studies have revealed that adults of both genders who sleep up to five hours a night are heavier than those who sleep seven hours or more. In UK, for example, only 20 % of the adults sleep the recommended eight hours a night.