The Alterations Of Circadian Rhythms Of Sleep-Wake, Rest-Activity In Aging And Its Relationship To Circadian Melatonin Rhythm

Objective: The alterations of circadian rhythms of melatonin secretion and sleep-wake, rest-activity rhythms in aging is not yet fully understood. Moreover, the relationship between circadian rhythm of melatonin and sleep-wake, rest-activity cycle is still uncertain. In present study, we investigated the alterations in sleep-wake, rest-activity patterns and in circadian rhythm of saliva melatonin during aging, special attention was paid to look the relationships between the rhythms of melatonin and sleep-wake, activity cycle.Method: A total number of 65 healthy volunteers in present study were divided into young, middle-aged, old and oldest groups. Each subject was taken a total of 12 time point salivary melatonin samples over 24-hours and recorded sleep-wake, rest-activity patters for five days using an actigraphy. The parameters of the circadian rhythm of melatonin secretion were derived from the basic cosine function.Results: The data derived from actigraphy and melatonin samples showed a significant alteration of circadian rhythm of sleep-wake, rest-activity and saliva melatonin secretion. A significant decreased actual sleep time and sleep efficiency and increased sleep latency, wake number, nap number and fragment index were found in aged people. A step-wise decrease in the amplitude of saliva melatonin secretion in early life, around 40 years of ages and an increase in daytime (baseline) melatonin levels were found in the old and oldest subjects. Although there is no significantdifference in acrophase of melatonin secretion among four groups, the phase-angel between bed time, wake time and melatonin acrophase was significantly altered with aging. In addition, the phase dispersion was significantly increased in old and oldest groups. Most strikingly, we found the significant positive correlations between amplitude of salivary melatonin and actual sleep time, sleep efficiency, wake number, sleep fragment index. Interestingly, acrophase of melatonin was positively correlated to the sleep latency. The negative correlation of wake number and the duration of melatonin secretion was found in present study.Conclusion: 1) The old people showed significantly weakened and fragmented circadian rhythms of sleep-wake, rest-activity during the course of aging. 2) Though the circadian rhythmity of salivary melatonin secretion still existed in old people, it significantly attenuated and desynchronized during the course of aging. 3) The correlation between the circadian sleep-wake cycle and the circadian rhythm of melatonin secretion indicated that melatonin secretion rhythm may play an important role in the circadian sleep-wake, rest-activity cycle. 4) The alterations of phase angle between sleep-wake cycle and melatonin rhythm in old people may have a causal relationship with their long sleep latency and early wakening in the morning.