A reduction in the time people spend asleep could partly account for soaring obesity rates, a study has revealed.
Less sleep led to higher levels of a hormone which increases hunger
Researchers at the University of Bristol have found that hormonal changes caused by lack of sleep could lead to increased appetite.
The population-based study examined more than 1,000 volunteers.
Report author Dr Shahrad Taheri said: "Individuals who spent less than eight hours sleeping were shown to have a greater likelihood of being heavier."
The research, carried out in conjunction with US scientists, is one of three published in recent weeks to produce similar results.
It found that people who habitually slept for five hours had 15% more ghrelin, a hormone which increases feelings of hunger, than those who slept for eight hours.
Those who slept for less time were also found to have 15% less leptin, a hormone which suppresses appetite.
"These differences are likely to increase appetite and, in societies where food is readily available, this may contribute to obesity," Dr Taheri said.
"It is important for people to realise there is more to obesity than just stuffing your face."
Sleep is important
Dr Taheri, whose work is published in the journal Public Library of Science Medicine, said there was evidence that children as young as two years old might be in danger of becoming obese if they lost a lot of sleep.
"We have to realise that sleeping is not a waste of time, we have to recognise that it impacts on our health."
The results of the study were replicated in a second piece of research, led by the University of Chicago.
This study found people who slept for only four hours a night for two nights had an 18% reduction in leptin, anda 28% increase in ghrelin.
The young men in the study also tended to eat more sweet and starchy foods when sleep was cut short.
A third recent study, by Columbia University, also found found people who slept four hours or less per night were 73% more likely to be obese.
Dr Neil Stanley, of the British Sleep Society, said not everybody needs a lot of sleep.
"There have been a number of people who have been famous for being short sleepers, most famously in our time Margaret Thatcher, who was renowned for only four hours, and before that people like Napoleon and Hitler.
"None of those was particularly large. But on the other side is Winston Churchill, who famously had his two hour nap in the afternoon, but also did not sleep very much during the evening, and cannot be said to have been a slender gentleman."