Sleep, cortisol awakening response and autonomic nervous system activity

Aim: Changes in modern lifestyle (sleep pattern, late-night high calorie diet consumption, multimedia usage, exercise etc.) may pose stress on the organism's daily activities by altering sleep quality. Under these circumstances, increased activities of the autonomous nervous system (ANS) and hypothalamo-pituitary-adrenal (HPA) axis may result in various pathophysiological outcomes. Therefore, the aim of the thesis was to find out the effects of modern lifestyle changes on sleep and stress axes (ANS and HPA) in short-term. Materials and methods: Activity of the HPA axis was evaluated by measuring cortisol in the salivary samples taken at 0, 15, 30 and 60 min post-awakening (cortisol awakening response, CAR). For the determination of the ANS activity, heart rate variability (HRV) was calculated from the electrocardiographic records (5 min). Six experiments were carried out for finding the effects of following situations on CAR and HRV: (1) sleep restriction (n=52), (2) changed sleep pattern (n=42), exercise before sleep (n=20), high calorie consumption before sleep (n=17), watching a screen before sleep (n=22) were investigated together with (6) determination of HRV-sleep-CAR relationships (n=48). Results: CAR was lower in sleep restriction but it was higher when sleep pattern was delayed and high calorie was consumed (p<0.05). However, exercise and watching a screen did not affect CAR (p>0.05). In general, HRV did not differ between the groups but decreased following exercise (p<0.05). Sympathetic activity was positively correlated with disturbed sleep (R2=0.284) while disturbed sleep was positively correlated with CAR (R2=0.278, p<0.05). Conclusion: As modern lifestyle changes resulted in deviations in the functions of the both stress axes, it may be suggested that these parameters are important markers for investigating pathophysiological mechanisms related to diseases of modern times (e.g. obesity, sleep problems, cardiovascular diseases).