by Lee Bowman
Scripps Howard News Service
December 07, 2004
Two new studies, published Monday and Tuesday, show that loss of sleep boosts levels of a hormone that tells us we're hungry, while dropping levels of a hormone that signals the body that we're full and should stop eating.
"Sleep is a major regulator of these two hormones," said Eve Van Cauter, a professor of medicine at the University of Chicago and lead author of one of the studies, published in the Annals of Internal Medicine.
Researchers have increasingly been noticing that increased obesity among Americans has coincided with less time spent asleep over the past several decades.
In 1960, U.S. adults slept an average of more than eight hours a night; by 2002, the average had fallen to less than seven hours. Sleep deficits are also being noted in children and teens. At the same time, in 1960, one in four adults was considered overweight and one in nine was considered obese; now two in three are overweight and nearly one in three is obese.
Rat studies have shown that the animals eat more when they're sleep-deprived. And a Columbia University study reported last month that there's a sliding scale of hours slept and obesity risk: people who get only two to four hours a night are 73 percent more likely to be obese than those getting seven or eight hours, while those getting 10 or more hours a night are 11 percent less likely to be obese.
Both Cauter's team and a group led by Dr. Shahrad Taheri at Stanford University (who is now at the University of Bristol in England) focused on the role of two key appetite hormones.
Leptin, a hormone produced by fat cells, gives out signals indicating whether energy reserves are dwindling and if the body needs to consume more calories. Ghrelin, mainly produced by the stomach, is a direct appetite trigger - the more hormone that's circulating in the blood, the more a person wants to eat.
"We found that people who slept for shorter durations have reduced leptin and elevated ghrelin. These differences are likely to increase appetite and, where food is readily available, may contribute to obesity," said Taheri, lead author of the report published online by the Public Library of Science.
For the Stanford study, carried out with researchers at the University of Wisconsin, the researchers looked at sleep patterns of more than 1,000 volunteers involved in a long-term study of sleep disorders. Seventy-four percent of this group slept less than eight hours a night.
The researchers found a 14.9 percent increase in ghrelin levels and a 15.5 percent decrease in leptin levels among people who consistently slept less than five hours a night vs. those who got eight hours of sleep.
"It was quite amazing that a hormone can track a person's self-reported amount of sleep so well," said Dr. Emmanuel Mignot, an associate professor of psychiatry and behavioral sciences at Stanford and a co-author of the study.
In the Chicago study, Van Cauter and colleagues studied 12 healthy male volunteers in their early 20s, measuring both their self-reported appetites and physically measured hormone levels after they'd gone two nights with only four hours in bed and again when they'd gotten an average of nine hours of sleep on two nights.
After a night with just four hours' sleep, the ratio of ghrelin to leptin increased by 71 percent compared to levels after longer sleep time.
The men reported a 24 percent increase in appetite on short sleep, with a surge in desire for sweets, like candy and cookies, salty foods like chips and nuts and starchy foods, like breads and pastas.
"We don't yet know why food choice would shift," Van Cauter said. "Since the brain is fueled by glucose, we suspect it seeks simple carbohydrates when distressed by lack of sleep." The researchers also note that the added difficulty of making decisions while sleepy may weaken motivation to select more nutritious foods.
"There is a sense that you can pack in more of life by skimping on sleep. But we are finding that people tend to replace reduced sleep with added calories, and that's not a healthy trade," Van Cauter said.
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