Background: Cortisol levels are increasingly often assessed in large-scale psychosomatic research. Although determinants of different salivary cortisol indicators have been described, they have not yet been systematically studied within the same study with a large sample size. Sociodemographic, health and sampling-related determinants of salivary cortisol levels were examined in a sample without potential disturbances because of psychopathology.
Methods: Using 491 respondents (mean age=43.0 years, 59.5% female) without lifetime psychiatric disorders from the Netherlands Study of Depression and Anxiety (NESDA), sociodemographic, sampling and health determinants of salivary cortisol levels were examined. Respondents collected seven salivary cortisol samples providing information about 1-h awakening cortisol, diurnal slope, evening cortisol and a dexamethasone (0.5mg) suppression test (DST).
Results: Higher overall morning cortisol values were found for smokers, physically active persons, persons without cardiovascular disease, sampling on a working day or in a month with less daylight. In addition, the cortisol awakening response was significantly flattened for males, persons with cardiovascular disease, those with late awakening times and those with longer sleep duration. Diurnal slope was steeper in men, physically active persons, late awakeners, working persons, and season with less daylight. A higher evening cortisol level was associated with older age, smoking and season with more daylight. Cortisol suppression after dexamethasone ingestion was found to be less pronounced in smokers, less active persons and sampling on a weekday.
Conclusion: Sociodemographic variables (sex, age), sampling factors (awakening time, working day, sampling month, sleep duration) and health indicators (smoking, physical activity, cardiovascular disease) were shown to influence different features of salivary cortisol levels. Smoking had the most consistent effect on all cortisol variables. These factors should be considered in psychoneuroendocrinology research.