Shortage of sleep is linked to obesity
By Roger Highfield, Science Editor
(Filed: 07/12/2004)
The less you sleep the more your waist will expand, say scientists
who have linked the insomniac lifestyle of western society to the
epidemic of obesity.
Lack of sleep boosts levels of a hormone that triggers appetite and
lowers levels of a hormone that tells your body it is full,
according to the team. The scientists will now study whether obese
people should sleep more to lose weight.
The study, by Prof Emmanuel Mignot of Stanford University, Dr
Shahrad Taheri of the University of Bristol and colleagues, is
published today in the Public Library of Science.
"Our results demonstrate an important relationship between sleep
and metabolic hormones," the team reports. "In western societies,
where chronic sleep restriction is common and food is widely
available, changes in appetite regulatory hormones with sleep
curtailment may contribute to obesity."
Dr Taheri said the team believed that sleeplessness contributed to
being overweight, and not the other way round.
As for the concern about children, obesity and television viewing,
he pointed out that watching television was often done at a time
when children should be sleeping.
While altering sleep duration was not going to be the complete
answer to the obesity pandemic, it may be an easy way to fight
it.
A study presented last month at a meeting of the North American
Association for the Study of Obesity, found that people who sleep
two to four hours a night were 73 per cent more likely to be obese
than normal sleepers. Researchers believe that sleep loss impacts
on several hormones related to appetite and food intake, and two
such hormones - ghrelin and leptin - are thought to play a role in
the interaction between short sleep duration and obesity.
Ghrelin, which was discovered five years ago and is primarily
produced by the stomach, triggers appetite so that the more ghrelin
you have, the more you want to eat.
Leptin, a hormone produced by fat cells, is a signal indicating
insufficient metabolic reserve and the need to eat more
calories.
The researchers from Stanford and Bristol examined the sleep
patterns of 1,024 volunteers.
The data showed a 14.9 per cent increase in ghrelin and a 15.5 per
cent decrease in leptin in people who consistently slept for five
hours compared with those who slept for eight.
Prof Mignot said the results were consistent regardless of gender,
size, eating and exercise habits. "The effect must be very strong
to appear in [this entire] population," he said. "It was quite
amazing that a hormone can track a person's self-reported amount of
sleep so well," he added.
The researchers also found that in people sleeping less than eight
hours (74.4 per cent of the sample), increased body mass index was
proportional to decreased sleep.
They reported that a 3.6 per cent increase in the index
corresponded to an average nightly sleep duration decrease from
eight hours to five hours. "Good sleep, healthy eating habits, and
regular exercise each may have important roles in fighting obesity
in modern society," said Prof Mignot.
