Previous studies concerning the relationship of serum testosterone levels to aging in normal men have yielded apparently inconsistent results. Studies performing blood sampling in the morning have often shown an age-related decrease in testosterone levels, while those using afternoon samples have failed to show such a decrease. These results suggested to us the possibility that the circadian rhythm in serum testosterone levels might be altered with normal aging in men. Hourly blood samples were obtained for 24 h from 1 young (mean age, 52.2 yr) and 12 old (mean age, 17 yr) healthy men. Total testosterone levels were measured by RIA. The circadian rhythm in serum testosterone levels found in normal young men was markedly attenuated or absent in healthy elderly men; the early morning rise in testosterone levels characteristic of young men was not present in old age. Mean testosterone levels for the entire 24-h day were lower in healthy old men than in young men. These results demonstrate a clear decrease in serum testosterone levels in healthy old men compared to those in young men and provide an explanation for the inability to demonstrate an age-related decline in testosterone levels in earlier studies using serum samples obtained in the afternoon.

Sleep and waking EEGs from 11 healthy nondemented elderly men and from ten inpatients for whom the diagnosis was probable senile dementia of Alzheimer's type (SDAT), were monitored in the subjects' typical home or ward environments or in the sleep laboratory, according to their customary sleep schedules. Aged normal subjects (age range, 56-85 years) had less Stage 3 and Stage 4 sleep, less REM sleep, and more wakefulness than normally observed in young adults. Patients with SDAT (age range, 56-88 years) had even less Stage 3 sleep, no Stage 4 sleep, and very little REM sleep, and experienced fragmentation of their sleep, with frequent awakenings. These sleep variables were significantly different in the SDAT and control groups (MANOVA). Examination of the 24-hour plots of sleep/waking patterns revealed prominent fragmentation of the diurnal sleep/waking rhythm in SDAT patients, with frequent daytime napping and nighttime periods of wakefulness. In addition, significant group differences were observed for the EEG variable, dominant occipital frequency. More qualitative EEG variables (diffuse slowing, spindle activity, and paroxysmal discharges) also differed between groups. It is suggested that correlative neuropathologic data might provide an understanding of the basis for the sleep, EEG, and mental-function factors that undergo change in SDAT.

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