Researchers from the University of Chicago report in the August 16 issue of JAMA that there are at least two stages of age-related deterioration of sleep quality and that, for men, the first stage occurs sooner than expected--between the ages of 25 and 45. They also found that changes in sleep were mirrored by changes in hormone secretion.
This was the first study to examine sleep quality and hormones influenced by sleep throughout adulthood, rather than comparing the sleep patterns and hormones of young versus old. The researchers collected data from sleep studies, conducted between 1985 and 1999, on 149 healthy men aged 16 to 83.
"Our study maps out the chronology of age-related changes in sleep duration and quality and suggests that altered levels of certain hormones may be a consequence of sleep decay," said Eve Van Cauter, Ph.D., professor of medicine at the University of Chicago and director of the study. "These changes in sleep quality provide an early biological marker of aging in men."
The first stage of deterioration of sleep due to aging occurs between young adulthood (ages 16 to 25) and mid-life (35-50). Although total sleep remained constant as young adults moved into mid-life, the proportion of slow wave or deep sleep decreased from nearly 20 percent of a normal night's sleep for those under 25 to less than five percent for those over 35. Growth hormone secretion, which occurs primarily during deep sleep, also declined by about 75 percent.
By the age of 45, note the authors, most men have almost entirely lost the ability to generate significant amounts of deep sleep. This study suggests that, as a consequence, most middle-aged men have very low levels of growth hormone.
Growth hormone deficiency has been studied extensively in the elderly, where it is associated with increased obesity, loss of muscle mass and reduced exercise capacity.