Circadian changes and seasonal variation in the salivary cortisol levels in elderly persons entering nursing homes

Abstract

Aim: We investigated circadian changes and seasonal variation in the salivary cortisol levels in elderly persons in nursing homes.
Methods: Circadian changes in the salivary cortisol levels were measured in the elderly subjects ten times every three hours from two hours at 21:00 from 6:00, three times at 6:00. The seasonal variation in salivary cortisol was determined according to a fixed method applied on one day between December and October (autumn), March and January (winter), June and April (spring) and September and July (summer). The samples were preserved in frozen storage in an exclusive freezer (at less than -20) and measured for the cortisol concentrations using EIA.
Results: Analyses using a general linear model of the salivary cortisol levels as the dependent variable and sex, age, season and time as independent variables showed that the primary factors affecting the salivary cortisol levels were time (morning>night), sex (male>female), age (B=0.1151) and season (autumn>summer). In addition, a meaningful interaction was observed between time and sex. Females exhibited higher levels at 6:00 than males, while males demonstrated a small decline from 6:00 to 11:00, which gradually continued thereafter.
Conclusions: The analysis of circadian changes showed high cortisol concentrations in females. It is necessary to consider daily changes, seasonal variation and sex differences when using the salivary cortisol level as an index of stress.