Aging diurnal rhythms and chronic stress: Distinct alteration of diurnal rhythmicity of salivary alpha-amylase and cortisol.

The present study assessed diurnal profiles of salivary alpha-amylase (sAA), proposed as a marker of autonomic activity, and salivary cortisol in competitive ballroom dancers as well as age- and sex-matched controls to investigate age-related changes of basal activity and potential chronic psychosocial stress-related alterations. According to the Allostatic Load (AL) hypothesis of a cumulative wear and tear of the body we expected to see physiological accumulation of the effects of stress and age especially pronounced in older dancers. Dancers and controls collected five saliva samples throughout the day. Daily overall output of sAA was elevated in older adults while there was no effect of age on mean cortisol levels. Alterations of diurnal rhythms were only seen in younger male dancers showing a flattened diurnal profile of sAA and younger dancers and female older dancers showing a blunted diurnal rhythmicity of cortisol. Furthermore, we found a negative correlation between summary indices of basal sAA and the amount of physical activity. In conclusion, higher overall output of sAA in older adults is in line with the phenomenon of a sympathetic "drive" with increasing age. Furthermore, a lower output of sAA in people who are more physical active is in line with the hypothesis of an exercise-induced decrease of sympathetic activity. Overall, our study does not support the AL hypothesis, but rather highlights the importance of regular physical activity and social environment in promoting health.