Melatonin secretion rhythm disorders in patients with senile dementia of Alzheimer’s type with disturbed sleep–waking

Background: There is growing evidence that the dysregulation of circadian rhythms may play an important role in irregular sleep–waking in demented elderly. In this study, we investigated daily variation of the pineal hormone melatonin, which has been reported to possess hypnogenic and synchronizing effects, in patients with senile dementia of Alzheimer’s type. Methods: Serum melatonin secretion rhythms in inpatients with senile dementia of Alzheimer’s type (SDAT group, n = 10, average age = 75.7 years) with disturbed sleep–waking and nondemented elderly (ND group, n = 10, age = 78.3 years) without clinical sleep disorders in the same facility were monitored under a dim light condition without excessive physical exercise. Results: The SDAT group showed a significantly higher degree of irregularities in actigraphically recorded rest–activity (R-A) rhythm during the 7-day baseline period compared with the ND group. The SDAT group simultaneously showed significantly reduced amplitude, larger variation of peak times, and diminished amount of total secretion in the melatonin secretion rhythm compared with the ND group. There were significantly positive correlations between the severity of R-A rhythm disorder and the reduced amplitude as well as diminished amount of total melatonin secretion. Conclusions: The SDAT patients with disturbed sleep–waking possessed melatonin secretion rhythm disorders that may play an important role in irregular sleep–waking in demented elderly.