Melatonin profile in healthy, elderly subjects - A systematic literature review

Melatonin plays an important role in regulation and maintaining of the circadian rhythm. In the elderly population, an array of disturbances of circadian rhythm and sleep can be observed; however the current knowledge within the group of healthy, elderly is scarce. This systematic literature review of studies on the melatonin profile measured in the blood of healthy, elderly individuals included 519 studies, found in the primary search on PubMed. After reviewing the title and abstract, 47 studies were found eligible for full text review. The inclusion criteria were defined as follows: healthy, elderly individuals, with a mean or average age over 65 years and analysis done in blood or plasma. In addition to the primary search, three studies were directly identified by the reference lists of already included studies. A final total of 23 studies were included in the systematic literature review. In reviewing the literature, a clear circadian melatonin profile with a nocturnal peak at 3 am and lower daytime levels was observed in the healthy, elderly population. In elderly over 75 years of age, the nocturnal level of melatonin may be lower; however, the circadian rhythmicity is maintained. In the comparison of elderly, independently living individuals and individuals living in care facilities, the latter group had lower levels of nocturnal melatonin peak as well as higher daytime levels; however one can wonder if elderly in care facilities are healthy. The 23 included studies in the systematic literature review had varying primary objectives and generally the term "healthy" within this population group proves difficult to clearly define. As a result of this, an obvious interstudy variability existed, which is a limitation of this systematic literature review. However, the graphs depicted represent the best possible estimation of the melatonin profile in a healthy, elderly population. Future research in the melatonin profile within this population should focus on clearly defined healthy elderly to ensure a valid normal material in this age group.