Exposure to real-ambient bedroom light at night delayed circadian rhythm in healthy Chinese young adults: A cross-sectional study.

BACKGROUND: Light at night (LAN) have attracted increased research attention on account of its widespread health hazards. However, the underlying mechanism remains unknown. The objective of this study was to investigate the effects of real-ambient bedroom LAN exposure on circadian rhythm among young adults and potential sex differences. METHODS: Bedroom LAN exposure was measured at 60-s intervals for 2 consecutive days using a portable illuminance meter. Circadian phase was determined by the dim light melatonin onset (DLMO) time in 7 time-series saliva samples. RESULTS: The mean age of the 142 participants was 20.7 ± 0.8 years, and 59.9% were women. The average DLMO time was 21:00 ± 1:11 h, with men (21:19 ± 1:12 h) later than women (20:48 ± 1:07 h). Higher level of LAN intensity (LANavg ≥ 3lx vs. LANavg < 3lx) was associated with an 81.0-min later in DLMO time (95% CI: 0.99, 1.72), and longer duration of nighttime light intensity ≥ 5lx (LAN5; LAN5 ≥ 45 min vs. LAN5 < 45 min) was associated with a 51.6-min later in DLMO time (95% CI: 0.46, 1.26). In addition, the delayed effect of LAN exposure on circadian phase was more pronounced in men than in women (all P-values <0.05). CONCLUSIONS: Overall, bedroom LAN exposure was significantly associated with delayed circadian rhythm. Additionally, the delayed effect is more significant in men. Keeping bedroom dark at night may be a practicable option to prevent circadian disruption and associated health implications. Future studies with more advanced light measurement instrument and consensus methodology for DLMO assessment are warranted.

Developmental Pattern of Diurnal Cortisol Rhythm and Sex-Specific Associations With Psychopathological Symptoms During Pubertal Transition.

OBJECTIVE: This study aimed to examine the developmental pattern of diurnal cortisol rhythm during pubertal transition and its prospective association with psychopathological symptoms. METHODS: A cohort of 1158 children consisting of 608 boys and 550 girls aged 7 to 9 years (mean [standard deviation] age = 8.04 [0.61] years) were recruited in the Anhui Province of China in 2015 (wave 1). A single awakening sample was collected at baseline, and three additional samples were collected at one weekday in wave 2 to wave 4. Four indices of cortisol activity were evaluated and calculated across the day: awakening cortisol level, cortisol awakening response, the area under the curve with respect to ground (AUC), and the diurnal cortisol slope. In each wave, pubertal development was assessed by testicular size in boys and Tanner scales in girls. Psychopathological symptoms were ascertained in waves 2 to 4. RESULTS: Multilevel mixed models revealed no significant pubertal changes in diurnal cortisol activity in girls. In boys, awakening cortisol (ß = -0.005, p = .004) and total cortisol output (lnAUC, ß = -0.005, p = .040) significantly decreased across pubertal transition. Higher awakening cortisol and total cortisol output (lnAUC) were associated with higher scores on internalizing symptoms in girls (ß = 0.82, p < .001; ß = 0.62, p = .012) and externalizing symptoms in boys (ß = 0.73, p = .001; ß = 0.55, p = .019) during the 3-year follow-up. In contrast, no associations were found between cortisol awakening response and diurnal cortisol slope with psychopathological symptom scores in boys or girls. CONCLUSIONS: Development of diurnal cortisol activity during pubertal transition occurs in a sex-specific manner. Awakening cortisol level and daily total cortisol output may serve as markers for psychopathology during pubertal transition.

Pubertal recalibration of cortisol reactivity following early life parent-child separation.

BACKGROUND: The hypothalamic-pituitary-adrenocortical (HPA) axis had been proved to calibrate to early-life adversity and puberty may reverse the calibration. This study examines the consequences of prolonged parent-child separation on HPA axis reactivity and the pubertal recalibration hypothesis. METHODS: Totally of 144 participants aged 8.75 to 15.25 (mean age 12.50 years, SD: 1.32) were enrolled from rural areas of Chizhou city, Anhui Province of China in 2019. Data on parent-child separation was collected from parents. Self-reported Peterson Pubertal Development Scale was used to assess pubertal maturation and HPA axis stress reactivity was measured using the Trier Social Stress Test for Children. RESULTS: For children at early stage of puberty, childhood parent-child separation experiences were associated with blunted HPA axis reactivity (B = -1.888, p = 0.034); while for those at later stage of puberty, HPA axis reactivity was similar between children experienced early childhood separation and those without separation (AUCi: B = -0.426, p = 0.878). In contrast, for children experienced persistent parent-child separation, blunted HPA axis reactivity was observed (all p < 0.05). LIMITATIONS: Due to the cross-sectional nature of this study, conclusions about causality remain speculative. CONCLUSIONS: The effect of parent-child separation on dysregulation of HPA axis acts in a time-dependent manner. This finding provides support for the pubertal recalibration hypothesis suggesting that a focus of improving environment in adolescence would help those individuals reared initially in non-supportive conditions.