The drop in growth hormone, in turn, is thought to lead to flab. Now, the researchers are working to see if new types of sleeping pills or hormone injections can slow signs of aging. The study of beauty sleep was limited to healthy men, and it is not clear whether the findings apply to women. Van Cauter and her team looked at sleep studies conducted on 149 men from 1985 to 1999. They found that by the time men reach age 45, they have nearly lost the ability to fall into deep sleep.
Men produce growth hormone primarily during that kind of sleep.
In studies of the elderly, growth hormone deficiency has been connected to obesity and the loss of muscle mass. The men involved in the sleep studies were of normal weight and ranged in age from 16 to 83. Researchers found that as the men moved into mid-life, from ages 35 to 50, their total amount of sleep remained fairly constant. The amount of deep, or slow-wave, sleep, however, decreased from nearly 20 percent of a normal night's sleep for men 25 or younger to less than 5 percent for those over 35. Growth hormone secretion declined by nearly 75 percent.