Study objectives: To examine sex effects on sleep stages and electroencephalogram (EEG) spectral power in older adults.
Design: Sleep was polygraphically recorded for 2 consecutive nights, and blood was sampled during the last 24 hours.
Setting: The University of Chicago Clinical Research Center.
Participants: Two groups of healthy nonobese older subjects: 10 men (59 +/- 2 years), and 10 postmenopausal women (63 +/- 2 years).
Measurements and results: A spectral analysis of the EEG was performed in the delta and alpha bands. There were no sex differences in sleep stages. Blood sampling resulted in reductions of total sleep time, sleep maintenance, slow-wave sleep, and absolute delta activity that were all larger in women than in men. In absolute values, delta and alpha activities in non-rapid eye movement (NREM) and rapid eye movement (REM) sleep were higher in women than in men, but, for delta activity, the sex differences were larger in REM than in NREM sleep. In women, but not in men, absolute delta activity in REM was decreased during blood sampling and was strongly correlated with absolute delta activity in NREM. Delta activity in REM did not dissipate across the night in either group. When normalized for the activity in REM sleep, the sex difference in delta activity in NREM sleep was reversed, with lower activity in women.
Conclusions: Sex differences in sleep EEG variables are present in older adults. When normalized, delta activity in older women is lower than in older men, which may be more consistent with sex differences in subjective complaints, in fragility of sleep in the presence of environmental disturbances, and in the relationship to growth-hormone release.