Physiological melatonin levels in healthy older people: A systematic review

Objective: Melatonin plays a major role in maintaining circadian rhythm. Previous studies showed that its secretion pattern and levels could be disturbed in persons with dementia, psychiatric disorders, sleep disorders or with cancer. Also ageing is a factor that could alter melatonin levels, although previous research provides contradicting results. As melatonin supplementation is increasingly applied in older persons as sleep medication, it is important to know if melatonin levels decrease in healthy ageing and/or secretion patterns change. The objective of this study is to determine physiological levels and secretion patterns of melatonin in healthy older people. Methods: We performed a systematic review and searched PubMed and Embase for studies published between January 1st 1980 and October 5th 2015 that measured melatonin in healthy persons aged >= 65 years. Results: Nineteen studies were retrieved. The number of participants ranged from 5 to 60 per study. Melatonin was mostly measured by radioimmunoassay (RIA) and the number of measurements per 24 hours varied from 1 to 96. Sixteen studies showed a secretion pattern with a clear peak concentration, mostly at 0200 h or 0300 h Maximum concentrations varied greatly from 11.2 to 91.3 pg ml(-1). Maximum melatonin level in studies with participants mean aged 65-70 years was 49.3 pg ml(-1) and in studies with participants mean aged >= 75 years 27.8 pg ml(-1), p-value <0.001. Conclusion: Total melatonin production in 24 hours seems not to change in healthy ageing, but the maximal nocturnal peak concentration of melatonin might decline. It is important to take this into account when prescribing melatonin supplementation to older people. (C) 2016 Elsevier Inc. All rights reserved.