Declining melatonin levels and older people. How old is old?

Objectives: The purpose of this study was to investigate whether melatonin levels in older cohorts within the 'aged' population were significantly lower than in younger 'aged' individuals and hence point to a possible confound in cross-sectional studies which group individuals over 55 in one category. Setting and design: Melatonin levels of 35 North Queensland residents over 55 years of age living in an aged-care facility, a retirement village or the general community were compared across three age groups. Methods: Subjects were ten 56-65 year olds, eighteen 66-75 year olds and seven over-75 year olds. Information was obtained on sleep, awakening, medical conditions and medications, with subsequent exclusion of those with known medical conditions and/or medications. Melatonin was collected by salivary samples at 2200 hours and concentrations were determined by immunoassay. Results: Mean melatonin levels were significantly lower (p=.03) in the 'oldest' (over 75 yrs) group compared to the 'youngest' (56-65 yrs) group. Main findings: The results of this preliminary study indicate that within the older population, melatonin levels appear to decline significantly with age. Conclusions: Future studies of melatonin and ageing may benefit from a longitudinal approach, with older subjects sampled across time. Copyright © Neuroendocrinology Letters.C