Growth hormone deficiency has been studied extensively in the elderly, and is associated with increased obesity, loss of muscle mass, and reduced capacity for exercise. Disordered sleep can reduce growth hormone secretion, and some experimental drugs that induce slow-wave sleep also increase growth hormone levels.
For the study, Van Cauter and colleagues analyzed data from 149 healthy men, aged 16-83 years, who had undergone sleep studies and for whom 24 hour measurements of cortisol and growth-hormone levels were available. The study included only men because women's sleep patterns do not deteriorate in early to mid-adulthood as men's do.
Louis J. McNabb, MD, of the Sleep Disorders Institute at St. Jude Medical Center in Fullerton, Calif., tells WebMD that Van Cauter's report raises an interesting question about the relationship between aging, sleep, and hormonal changes. But McNabb says this observation doesn't show that losing sleep causes these hormonal changes or vice versa.
"Going from the observation that these changes occur together to the conclusion that there is a causal relationship is a long leap," McNabb, who was not involved in the study, tells WebMD.
Even if there is a causal relationship, McNabb is not convinced it is clinically important. "Is the question whether men over age 55, most of whom have these sleep and growth hormone changes, can function well on a daily basis? If so, the answer is yes. The heads of most of our major corporations are over 55. Most of our presidents have been over 55. Most men do just fine regardless of the age-related drop-off in delta or slow-wave sleep."
The most intriguing possibility raised by Van Cauter's research is that restoring SW sleep might reverse the decline of growth hormone in young to middle-aged men and thus protect against some of the physical changes associated with aging.
Marc R. Blackman, MD, a renowned growth hormone researcher and author of an editorial accompanying the study, writes that "therapeutic interventions [to prevent these age-related changes] should be assessed relatively early in life. ... Clearly, more research into this promising area is indicated, as the potential benefits to the aging population are substantial." Blackman is with the department of medicine at The Johns Hopkins University School of Medicine in Baltimore.