Sex hormones, sleep, and core body temperature in older postmenopausal women.

UP TO 50% OF MEDICALLY HEALTHY WOMEN OVER THE AGE OF 60 YEARS REPORT SLEEP DISTURBANCE.1–6 THESE SUBJECTIVE PERCEPTIONS OF POOR SLEEP QUALITY have been verified objectively in the laboratory. For example, with time in bed held constant, older women exhibit total sleep times approximately 2 hours shorter than those of young adults.7–9 Sleep also appears to become “shallower,” and more easily interrupted with age, as reflected in significant declines in electroencephalogram slow-wave activity, increases in wake time after sleep onset (WASO), and decreased arousal thresholds. 10–13 Older women who complain of sleep disturbance most often report difficulty maintaining, rather than initiating, sleep.14–16 They report particular difficulty maintaining sleep in the second half of the night and, as a result, often terminate their night's sleep prematurely. In the laboratory, not only do older women exhibit more spontaneous awakenings than do younger subjects, but they take almost 4 times longer to return to sleep than their younger counterparts.16 A constellation of risk factors for sleep problems in aging women has been identified,5, 17–19 and it is clear that several age-related physiologic changes interact to produce the disturbed regulation of sleep. One aspect of aging that has received sparse attention, however, with regard to effects on sleep, is the dramatic reregulation of reproductive hormones that occurs at menopause and continues throughout the postmenopausal period. Few studies have measured gonadal hormones in women who are more than a couple of years postmenopause, and almost no studies have investigated, beyond menopause, whether endogenous levels of these hormones influence sleep. Yet, perimenopausal and postmenopausal women share many of the same features of sleep disturbance, such as awakening in the early morning hours and an inability to return to sleep. Furthermore, several studies have shown that hot flashes and other vasomotor symptoms that influence sleep continue years beyond menopause in up to 40% of postmenopausal women.20, 21 Thus, the sleep difficulties that emerge at menopause often do not abate and may become compounded by age-associated disruption of circadian and homeostatic processes that regulate sleep.22–24 Sleep disturbance during the climacteric has generally been associated with estrogen deficiency, and there is evidence that estrogen plays an important role. For example, exogenous estrogen therapy has been reported to improve subjective and, to a lesser extent, objective sleep, most often attributable to a decrease in hot flashes. Nevertheless, a substantial proportion of older women who take estrogen have residual sleep complaints. In addition, many older women experience sleep disturbance that may be associated with age-related changes in thermoregulation25 in the absence of hot flashes or night sweats. Whether the postmenopausal sex hormonal milieu is associated with sleep in these women has not been investigated to any extent. As emphasized by Moe (1999), “There is virtually no information available about how the postmenopausal hormone profile interacts with the sleep of older, asymptomatic postmenopausal women26, p344.” The current study was undertaken to add to the literature relating to postmenopausal sex hormone levels and sleep. It was designed to exploit the well-documented variability in sleep among older women to examine potential relationships between objective sleep measures, nocturnal sex hormone levels, and the nocturnal course of body core temperature.