Differential pattern of the circadian rhythm of serum melatonin in young and elderly healthy subjects.

The daily profile of serum level of melatonin was studied in 10 young and 13 elderly subjects. All of the subjects were physically and psychiatrically healthy and did not have any clinical symptoms related to rhythm disturbance. Blood samples were taken every 3 h for 1 day and serum melatonin levels were determined by RIA. All except for 1 of the elderly subjects exhibited a clear circadian rhythm of serum melatonin level with a nocturnal peak. In both subject groups, the melatonin rhythm showed significant diurnal variation. There was no significant difference in the total melatonin level per day between young and elderly groups, suggesting that there was no influence of aging on daily total melatonin secretion. However, there was a marked difference in the features of the melatonin rhythm between the two groups, i.e., a rapid decline of the melatonin level from the nocturnal peak in the elderly group, suggesting that the off-set time of melatonin secretion advances with aging. Our findings suggest that the pattern of melatonin rhythm alters significantly without clear clinical symptoms in the process of senescence.