This week researchers from the University of Chicago published a study in the Journal of the American Medical Association that looked at sleep and its relationship to the body's natural chemistry, particularly growth hormone and cortisol, a hormone the body produces in times of stress. The study followed 149 healthy men without sleep complaints or histories of psychiatric or hormonal disorders in a sleep laboratory where blood was drawn from the volunteers before, during and after sleep.
What researchers found suggests that sleeping could be doing you more good than just resting your eyes. The study already confirmed a well-known fact that our total sleep time decreases with age, with significant reductions found after midlife. From midlife until the 80s, the total sleep time decreased on average by 27 minutes per decade. It also showed that the older the volunteers, the more awakenings they experienced through the course of the night and the less time they spent in REM (rapid eye movement), when we tend to dream. And aging didn't just affect the quantity of sleep; it also had an impact on quality. From early adulthood ( ages 16-25) to midlife (36-50), the percentage of deep slow wave (SW) sleep decreased from 18.9 percent to 3.4 percent.
The reason these two factors are important is because of the substance that helps keep your bones massy and your muscles toned: Growth hormone. Several studies have shown that the release of growth hormone is tied to our sleep. Because men secrete 60 to 70 percent of their daily GH during sleep, especially during the SW phase, the authors suggest that the less time is spent in SW sleep, the less GH is secreted into the blood. And GH secretion decreases by nearly 75 percent from young adulthood to midlife: According to one of the study's author's, Eve Van Cauter, Ph.D., "A young healthy man will have 100 minutes of deep sleep in a normal eight-hour night. A 45-year-old man may have 15 minutes or even 10 or 5 minutes."
This drop in GH could mean a lot to you, especially since it's directly linked to all the signs associated with aging. Less GH means less muscle and strength, more fat and flab, weaker bones and decreased immune system function. Receiving GH injections has long been a growing trend in this country, and much of it is based on replenishing our body's natural stores. Much controversy exists surrounding the effectiveness and safety of these injections, but some anti-aging doctors regularly administer these shots to their patients.
So what about the women? The authors say they focused their studies only on men because the predominant GH release occurs during sleep in men but not women. They also note that evidence suggests that as women age, they don't experience the same decline in sleep patterns as men. This will remain a big question mark until further studies shed more light on the female experience. Regardless of your gender, one thing is for sure: Getting more sleep could be exactly what the doctor ordered.