Physical activity and hypothalamic–pituitary–adrenocortical axis function in adolescents

Summary

Little is known about the associations between physical activity (PA) and hypothalamic–pituitary–adrenocortical axis (HPAA) activity in adolescents. This knowledge could offer insight into the links between PA and well-being in youth. We studied whether objectively-measured PA is associated with diurnal salivary cortisol responses and morning salivary cortisol responses after a low-dose overnight dexamethasone suppression test (DST) in adolescent girls and boys. We conducted a cross-sectional birth cohort study in Helsinki, Finland. At a mean age of 12.4 (SD = 0.5) years, 150 girls and 133 boys wore wrist-worn accelerometers over at least 4 days to measure PA. Their salivary cortisol was measured across 1 day and upon awakening after a low-dose overnight DST (3 μg/kg of weight). Girls with higher overall PA and vigorous PA (VPA), and less sedentary time had lower salivary cortisol upon awakening and/or after (decreases between |0.17| and |0.25| SDs per SD increase in overall PA, VPA and decrease in sedentary time; P-values < 0.039). Boys with higher overall PA, and less sedentary time had greater suppression of salivary cortisol following overnight DST (suppression between |0.24| and |0.27| SDs per SD increase in overall PA and decrease in sedentary time; P-values < 0.012). Overall PA, VPA and sedentary time did not associate with DST suppression in girls or with diurnal salivary cortisol in boys. These results show that PA is associated with altered HPAA function in early adolescents, and that the associations are sex specific.

Introduction

Higher physical activity (PA) levels are associated with several benefits for physical and mental well-being (Physical Activity Guidelines Advisory Committee, 2008). Hypothalamic–pituitary–adrenocortical axis (HPAA) activity has been suggested to play a role in mediating these associations (Hackney, 2006, Klaperski, 2013, Martikainen et al., 2013), though very few studies have examined the associations of daily PA levels and HPAA activity. In 46 young adult men and women, higher objectively measured vigorous PA (VPA) was associated with higher hair cortisol concentrations (Gerber et al., 2013), presumably reflecting the long term accumulation of higher levels of cortisol after bouts of intense physical activity. In another study of 491 adult men and women, higher overall levels of self-reported PA were associated with elevated morning cortisol, steeper diurnal cortisol decline, and greater cortisol suppression after the dexamethasone suppression test (DST) (Vreeburg et al., 2009), suggesting a more dynamic HPAA.

To our knowledge only one previous study in children has tested the association between PA and HPAA activity. We have demonstrated that in pre-pubertal 8-year-old children objectively measured overall PA, and time spent in sedentary or VPA were not associated with diurnal salivary cortisol pattern, though we did find that higher levels of PA were associated with lower salivary cortisol responses during a psychosocial stress test (Martikainen et al., 2013). However, it is not appropriate to extrapolate data from a study in children to adolescents. Adolescence is a period that comprises multiple changes in lifestyle and physiology, as well as psychology. The level of PA decreases from childhood to adolescence, accompanied by an increase in sedentary time (Basterfield et al., 2011, Ortega et al., 2013), whereas HPAA activity increases along with age and pubertal maturation (Gunnar et al., 2009).

Diurnal salivary cortisol does not either provide information on the individual variation of HPAA feedback inhibition. Therefore, in this study we tested if objectively-measured overall levels of PA, time spent in VPA, and sedentary time in adolescent girls and boys, at a mean age of 12 years, are associated with diurnal salivary cortisol and salivary cortisol upon awakening after a low-dose overnight DST. We conducted the analyses separately in girls and boys as HPAA activity is closely interlinked with sex steroid production and sex-specific differences in HPAA activity emerge during adolescence, although results on the direction of these differences remain inconsistent (Adam et al., 2010, Bouma et al., 2009, Gunnar et al., 2009, Reynolds et al., 2013). Further, boys often lag behind girls in pubertal maturation (e.g., Pesonen et al., 2014), which might be another source of sex-related variation in HPAA activity and function in adolescence.