Low cortisol and a flattening of expected daytime rhythm: potential indices of risk in human development.

Since the work of Hans Selye, stress has been associated with increased activity of the limbic-hypothalamic-pituitary-adrenocortical (LHPA) axis. Recently, a number of studies in adults have shown that this neuroendocrine axis may be hyporesponsive in a number of stress-related states. Termed hypocortisolism, the paradoxical suppression of the LHPA axis under conditions of trauma and prolonged stress presently challenges basic concepts in stress research. Adverse conditions that produce elevated cortisol levels early in life are hypothesized to contribute to the development of hypocortisolism in adulthood. However, as reviewed in this paper, hypocortisolism also may be a common phenomenon early in human childhood. Although preliminary at this point, the ubiquity of these findings is striking. We argue that developmental studies are needed that help explicate the origins of low cortisol and to determine whether the development of hypocortisolism is, in fact, preceded by periods of frequent or chronic activation of the LHPA axis. We also argue that developmental researchers who incorporate measures of salivary cortisol into their studies of at-risk populations need to be aware of the hypocortisolism phenomenon. Lower than expected cortisol values should not necessarily be relegated to the file drawer because they contradict the central dogma that stress must be associated with elevations in cortisol. Lastly, we note that evidence of low cortisol under adverse early life conditions in humans adds to the importance of understanding the implications of hypocortisolism for health and development.