The salivary alpha amylase over cortisol ratio as a marker to assess dysregulations of the stress systems

Abstract

Different factors have been associated with changes in the regulation of the two major stress response systems of the human body, the sympathetic nervous system (SNS) and the hypothalamic-pituitary-adrenal (HPA) axis. Changes in these systems have been associated with various (psycho)pathologies across adulthood, and are thus frequently assessed within the context of allostatic load. Early Life Adversity (ELA) has been identified as one such factor. Individuals with histories of ELA show evidence of elevated basal and reactive salivary alpha amylase (sAA) levels (a marker of SNS activity), blunted cortisol levels (a marker of HPA axis activity), and an asymmetrical relationship between the two variables. However, variable methods used in the past to measure each variable, and the relationship between the two systems, prevent us from drawing firm conclusions. This preliminary study investigated whether the ratio of reactive sAA over reactive cortisol would be more informative to investigate the relationship between the two stress systems than the ratio of cortisol over sAA, or either marker alone, and whether there is a systematic link between this marker and subjective indexes of chronic stress and depression. We studied this in a total of 37 subjects (n=20 with signs of early life adversity and n=17 without) exposed to the Trier social stress test. Using a specific formula to determine the ratio of sAA over cortisol, we found a systematically stronger positive relationship with indexes of chronic stress and depression when compared to cortisol over sAA, or either marker alone. Our findings suggest that the ratio of sAA over cortisol might be a better marker of stress systems dysregulation than the ratio of cortisol over sAA, sAA or cortisol alone. The usefulness of this marker for other chronic stress states as found in allostatic load is discussed.