Not All Stress Is the Same: Variable Associations Between Psychosocial Stressors and Urinary Cortisol Rhythms in a...

Dysregulations of the hypothalamic-pituitary-adrenal (HPA) axis have been linked to adverse health outcomes such as obesity, cardiovascular disease, and diabetes. While research on the HPA axis is growing, few studies have examined whether different types of stressors affect HPA functioning differently, and none have done so in small-scale subsistence populations. To do so, we measured HPA axis activity and various kinds of stressors among the Tsimane of Bolivia, a population with more traditional lifestyles and stressors including low caloric intake, social conflict, and market integration.

Participants were adults from three different Tsimane communities (n = 129, 57% women). For each participant, urinary cortisol (n_samples = 303), corrected for specific gravity, was measured once at waking and at least once later on the same day to measure the diurnal slope. One hundred and twenty-five participants completed a questionnaire on culturally relevant psychosocial stressors in the Tsimane such as food insecurity, social conflicts, and economic problems. Multilevel Bayesian multivariate models assessed associations between stressor scores and cortisol levels.

Diurnal variation in the HPA axis was differentially associated with each type of stressor. Food insecurity was associated with higher morning levels (median r_intercept = 0.08, p _> 0= 0.73) and a steeper diurnal slope (median r_slope = -0.19, p _< 0 = 0.83), while economic problems were associated with lower waking levels and shallower slopes (median r_intercept = -0.05; p _< 0 = 0.64, median r_slope = 0.12, p _> 0= 0.72). Higher morning levels and steeper slopes were also associated with better self-rated health (median r_intercept = 0.06; p _< 0 = 0.66, median r_slope = -0.10, p _> 0 = 0.71).

While many of these associations had high statistical uncertainty due to wide posterior distributions, the results overall emphasize complex relationships between perceived stressors and diurnal cortisol rhythms among a small-scale subsistence-based society. Future work employing longitudinal designs and higher-resolution sampling will be needed to clarify these trends.