Changes in cortisol and growth hormone secretion during nocturnal sleep in the course of aging

Background. One current hypothesis of biological aging proposes that aging results from the deterioration of neuroendocrine functions. Sleep dependent growth hormone (GH) secretion is diminished in elderly people. However, the time course of this decrease from puberty to senescence is still unknown. Cortisol secretion is also related to sleep processes with the 24 hr nadir occurring, like the sleep dependent GH secretory surge, during the first half of nocturnal sleep. Whether age also affects the sleep-associated nadir of cortisol secretion has yet to be clarified. This study investigated changes in GH and cortisol secretion during sleep in 30 male volunteers age 20 to 92 yr. Methods. After an adaptation night, each subject spent another night in the sleep laboratory for polygraphic sleep recording and determination of GH and cortisol levels every 15 min. Results. GH peak values exponentially decreased with age (r = -.80, p < .001), while the cortisol nadir increased linearly as a function of age (r = .79, p < .001). Age-related changes in sleep-dependent secretion of GH and cortisol correlated significantly (r = .47, r = -.55, respectively; p < .05) with an age-dependent decrease in slow wave sleep. Conclusion. Alterations of GH peak amplitude and basal cortisol secretion are not restricted to senescence. These changes develop gradually during adult life with different time courses. Both changes in GH and cortisol secretion may act together to reduce anabolic functions of sleep in the aged.