Upright posture influences salivary cortisol

This study was designed to investigate the influence of posture on salivary cortisol concentrations in healthy volunteers. In a balanced cross-over design 24 subjects were exposed at 1 week intervals to different body positions (sitting [S], lying [L] upright [U]) for 20 min in each condition. Before, during and after the experimental treatment measures of blood pressure, heart rate and saliva samples for determining the free fraction of cortisol were obtained. Furthermore, at corresponding time points a questionnaire on emotional states was completed. In addition, subjects were requested to complete personality questionnaires before the experiment and to rate their emotional states during saliva sampling. Results clearly indicate that the circadian decrease of cortisol concentrations was present only in the conditions [S] and [L] whereas in [U] salivary cortisol concentrations increased significantly. As expected, heart rate accelerations associated with a marked reduction of systolic blood pressure were observed in [U]. To further examine the relationship between hormonal and cardiovascular responses as indicators of autonomic activation, correlations between change scores were computed indicating that a relationship between cardiovascular responses and cortisol increases is not restricted to [U]. Positive correlations were observed between changes in systolic blood pressure and changes in cortisol concentrations in both conditions [U] and [L]. Posture does not affect emotional states indicating independence between posture induced physiological responses and experienced discomfort. Posture therefore should be adequately controlled, since those non-specific increases of hormones may interfere with state or trait dependent responses. Data are discussed with respect to the importance to control for posture in field and experimental studies and to possible mechanisms of posture induced changes in cortisol.