Circadian variations in the elderly: A scoping review.

The circadian clock plays important roles in several physiological processes. With aging, some of these circadian rhythms have been shown to be disrupted and suggested contributing to age-related diseases. The aim of this scoping review was to examine and map the existing evidence of circadian differences between young and older people in body fluid composition. Literature search was carried out on PubMed, Embase, Scopus and OpenGrey. The studies were screened based on inclusion and exclusion criteria by two independent reviewers and the results were summarized tabularly and narratively. The review process resulted in the identification of 1889 publications, of which 42 were eligible for inclusion. Forty-eight parameters or families of parameters were identified, including cortisol and melatonin, sex hormones, thyroid-related hormones, steroids and aldosterone. However, many were reported by only a single study. The results from the studies were heterogeneous. Even though the majority suggested the flattening of several circadian oscillations in the elderly population, this was not always observed for all the parameters analyzed, and some contradictory results were found. This review revealed a substantial number of publications that explored this research question, but further studies would be important to elucidate the clinical significance of these alterations.