Developmental Trajectory And Sex Differences Of HPAAxis Cortisol Circadian Rhythm During Puberty

Objectives The study aims to clarify the characteristics of the circadian rhythm of the hypothalamic-pituitary-adrenal(HPA)with age and pubertal development,as well as possible sex differences in these developmental changes.Methods Based on the child cohort in Ma'anshan of Anhui Province established in 2015(wave1),with informed consent,1167 students of grades 2 to 3 were selected in 2016(wave 2)(average age was 9.08 years,female was accounted for 47.9%),and follow-up surveys were conducted in 2017(wave 3)and 2018(wave 4),respectively.Demographic information including birth date,falling asleep and getting up time was collected through questionnaire investigation,and pubertal development in boys and girls were evaluated by testicular volume measurement and breast development Tanner staging,respectively.Height and weight were assessed during each follow-up and body mass index(BMI)was calculated.In wave 1,awakening saliva was collected in the morning of one school day;in wave 2to wave 4,3 saliva samples were collected in the morning of one school day:immediately after waking in the morning,30 minutes after waking,and before bed at night.Salivary cortisol concentration was assessed.Four HPA-axis circadian rhythm indicators were calculated: morning awakening cortisol,cortisol awakening response(CAR),daytime cortisol area under curve(AUC)and diurnal cortisol slope(DCS).Among them,CAR,AUC and DCS were conducted log conversion respectively.The comparison of HPA-axis circadian rhythm indicators in baseline and follow-up and at different developmental stages of puberty was use non-parametric test;using multi-level mixed model(multilevel mixed model)to identify the changes that HPA axis circadian rhythm indicators with age and puberty in boys and girls,to calculated the predicted values of circadian rhythm of HPA axis in boys and girls respectively,to analyzed the correlation between the predicted values and the female Tanner stage and the male testicular volume.Results The results of multi-level mixed model showed that during the follow-up period,cortisol levels at three time points(immediately after awakening,30 minutes later and before bedtime)showed wave 4 higher than wave 2,and the difference was statistically significant(Z = 14.13,9.95,14.13,respectively;all P < 0.001).The predicted values of awakening cortisol,lg CAR,lg AUC and lg DCS were significantly correlated with age(? was 0.01,-0.05,0.02,0.19,respectively;all P <0.001).With the increase of age,awakening cortisol,lg AUC and lg DCS showed an increasing trend,and the gender difference was not statistically significant.lg CAR showed a decreasing trend with age,and the lg CAR level of girls was significantly higher than that of boys.lg DCS showed an increasing trend with age,suggesting a flattening trend of circadian rhythm of HPA axis during this period.After controlling for age,internalizing symptoms,BMI,adverse childhood experiences,household economic status,parental education,sleep duration,wave,no significant association was found between HPA axis circadian rhythm indicators,including awakening cortisol concentration,lg CAR,lg AUC,lg DCS with breast Tanner stage in girls(?=-0.04,P=0.40;?=-0.06,P=0.79;?=-0.01,P=0.25;?=-0.07,P=0.52).In boys,awakening cortisol and lg AUC was found negatively associated with testicular volume(?=-0.06,P=0.01;?=-0.05,P=0.03),while no associations were found between lg CAR and lg DCS with testicular volume(?=-0.001,P=0.97;?=-0.09,P=0.09).Conclusion This study explored the developmental changes in circadian rhythm of HPA axis with age and pubertal development based on 3-year follow-up.Results suggested that awakening cortisol,total amount of diurnal cortisol secretion and diurnal cortisol slope increased with age,while cortisol awakening response decreased with age.These findings suggested a flattened trend of circadian rhythm.In boys,awakening cortisol and total amount of diurnal cortisol secretion decreased with testicular volume.No associations between HPA axis circadian rhythm indicators with breast Tanner stage were found in girls.