Obesity due to chronic sleep deprivation

Two new studies, published today, show that too little sleep can lead to higher levels of a hormone that triggers appetite, and lower levels of a hormone that tells your body it's full and has enough fuel.

The result: The less you sleep, the more you eat -- and the more weight you gain.

In the paper, published in the medical journal Public Library of Science Medicine, researchers speculate that sleep loss has an impact on several hormones related to appetite and food intake. They said two such hormones -- ghrelin and leptin -- are thought to play a role in the interaction between short sleep-duration and high body-mass index (an approximation of body fat based on height and weight).

Ghrelin, which is primarily produced by the stomach, triggers appetite in humans: The more ghrelin you have, the more you want to eat.

Leptin, a hormone produced by fat cells, tells the body that its energy stocks are low and that there is a need to consume more calories. Low leptin levels are a signal for starvation and increased appetite.

Dr. Taheri and his colleagues found that people who normally slept for five hours nightly produced 14.9 per cent more ghrelin than those who slept for eight hours. They also produced 15.5 per cent less leptin. The results held regardless of gender, eating patterns or exercise habits.

A second, unrelated study, published in today's edition of the Annals of Internal Medicine, also found a link between sleep and hunger hormones. Researchers at the University of Chicago took 12 healthy young men and allowed them to sleep only four hours nightly. The result, after only two nights of sleep deprivation, was a 28-per-cent increase in ghrelin and an 18-per-cent drop in leptin. In addition, participants reported not only being hungrier, but craving calorie-dense, high-carbohydrate foods such as chips and cookies.