Lead exposure, glucocorticoids, and physiological stress across the life course: A systematic review

Abstract

The biological pathways linking lead exposure to adverse outcomes are beginning to be understood. Rodent models suggest lead exposure induces dysfunction within the hypothalamic-pituitary-adrenal (HPA) axis and glucocorticoid regulation, a primary physiological stress response system. Over time, HPA axis and glucocorticoid dysfunction has been associated with adverse neurocognitive and cardiometabolic health, much like lead exposure. This systematic review utilized PRISMA guidelines to synthesize the literature regarding associations between lead exposure and downstream effector hormones of the HPA axis, including cortisol, a glucocorticoid, and dehydroepiandrosterone (DHEA), a glucocorticoid antagonist. We additionally determined the state of the evidence regarding lead exposure and allostatic load, a measure of cumulative body burden resultant of HPA axis and glucocorticoid dysfunction. A total of 18 articles were included in the review: 16 assessed cortisol or DHEA and 3 assessed allostatic load. Generally, the few available child studies suggest a significant association between early life lead exposure and altered cortisol, potentially suggesting the impact of developmental exposure. In adulthood, only cross sectional studies were available. These reported significant associations between lead and reduced cortisol awakening response and increased cortisol reactivity, but few associations with fasting serum cortisol. Two studies reported significant associations between increasing lead exposure and allostatic load in adults and another between early life lead exposure and adolescent allostatic load. The paucity of studies examining associations between lead exposure and allostatic load or DHEA and overall heterogeneity of allostatic load measurements limit conclusions. However, these findings cautiously suggest associations between lead and dysregulation of physiological stress pathways (i.e., glucocorticoids) as seen through cortisol measurement in children and adults. Future research would help to elucidate these associations and could further examine the physiological stress pathway as a mediator between lead exposure and detrimental health outcomes.

Keywords: Cortisol; HPA axis; Lead exposure; Life course; Physiological stress systems; Systematic review.