Daily and seasonal rhythms of interleukin 6 and cortisol levels in saliva and some lifestyle habits of medical students in Poland

Objective A primary aim of this study was to establish possible daily and seasonal rhythms of interleukin 6 and cortisol in the saliva using 15 healthy female volunteers. Methods All of the females were at the same stage of their menstrual cycle (follicular or luteal) during the two seasons tested. Twelve saliva samples were taken at 20 h, 22 h, 24 h, 02 h, 04 h, 06 h, 08 h, 10 h, 12 h, 14 h, 18 h and 20 h the next day, during one of the days of the two seasons tested (in January/February and May/June). Additionally, each subject filled out a questionnaire regarding her lifestyle habits. The volunteers answered questions regarding their sleep time, food and fluid intake, and the amount of physical activity undertaken on a weekday and weekend of each season tested. The study adhered to the Principles of the Declaration of Helsinki. Results There is a statistical difference between cortisol concentrations during the seasons, with a higher level of cortisol during the summer. However, there was no statistica...