Circadian variations of cortisol, melatonin and lymphocyte subpopulations in geriatric age

A number of age-related changes in the 24-hour hormonal and non-hormonal rhythms have been found in older human beings. Lymphocyte subpopulations present circadian variation of some of their subsets and this variation may influence magnitude and expression of the immune responses. Numerous interactions exist among the nervous, endocrine and immune systems, mediated by neurotransmitters, hormones and cytokines. The aim of this study is to evaluate circadian variations of some endocrine and immune factors in older adults. Cortisol and melatonin serum levels were measured and lymphocyte subpopulation analyses were performed on blood samples collected every four hours for 24 hours from ten healthy young and middle-aged subjects and from ten healthy elderly subjects. There was a statistically significant difference between the groups in the observed values of CD20 (higher in young and middle-aged subjects) and CD25 and DR+ T cells (higher in elderly subjects). In the group of young and middle-aged subjects a clear circadian rhythm was validated for the time-qualified changes of all the factors studied. In the group of elderly subjects a number of rhythms were absent or altered. The results of the current study show that aging is associated with enhanced responsiveness of T cell compartment and alterations of circadian rhythmicity.