Fat chance for the sleepless

WASHINGTON - People who put on a few extra kilos may be able to blame a lack of sleep for the added weight, according to two separate studies published yesterday.

Losing sleep can raise levels of hormones linked with appetite and eating behaviour.

In one study, people who slept only four hours a night for two nights had an 18 per cent reduction in leptin, a hormone that tells the brain there is no need for more food, and a 28 per cent rise in ghrelin, which triggers hunger.

The young men in the study also tended to eat more sweet and starchy foods when sleep was cut short.

"We don't yet know why food choice would shift," said study leader Eve Van Cauter, a professor of medicine at the University of Chicago.

"Since the brain is fuelled by glucose, we suspect it seeks simple carbohydrates when distressed by lack of sleep ... we are finding that people tend to replace reduced sleep with added calories."

Van Cauter and colleagues wrote in the Annals of Internal Medicine that they studied 12 healthy men in their early 20s.

They measured circulating levels of leptin and ghrelin before the study, after two nights of only four hours in bed, and after two nights of 10 hours in bed.

"We were particularly interested in the ratio of the two hormones - the balance between ghrelin and leptin," Van Cauter said.

After four hours of sleep, the ratio of ghrelin jumped 71 per cent compared with a night when the men slept nine hours.

The sleep-deprived men chose sweets, biscuits and cake over fruit, vegetables or dairy products.

A second study found that the less people slept, the more they weighed, using a measure called body mass index, which scales weight to height.

It also found lower leptin levels and higher ghrelin levels in people who slept less.

In the Wisconsin Sleep Cohort Study, Dr Emmanuel Mignot, of Stanford University in California, and colleagues examined 1000 people, measuring sleep habits and leptin and ghrelin levels.

They found people who consistently slept five hours or less each night had on average 14.9 more ghrelin and 15.5 per cent lower leptin levels than those who slept eight hours a night.

"Our results demonstrate an important relationship between sleep and metabolic hormones," the researchers wrote in the Public Library of Science Medicine journal.

"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."

- REUTERS