Circadian amplitude and CLOCK 3111 polymorphism predict morning leptin in Arctic residents, independent of photoperiod.

CLOCK rs1801260 and MTNR1B rs10830963 Polymorphisms Modulate the Association between Cholesterol Levels and Circadian Rhythms in Arctic Residents

Circadian phenotype is associated with diurnal variation in human exercise performance.

PURPOSE Time-of-day variation in exercise performance is well established, but the contribution of circadian phenotype to the magnitude of these differences remains unclear. This study examined diurnal variation in aerobic exercise performance and determined whether chronotype and sleep timing were associated with morning-evening differences in performance. METHODS Twenty-four healthy young adults (12 male, 12 female) completed a randomised crossover protocol consisting of a 10-min cycling time trial performed in the morning (08:00-09:00) and evening (17:00-18:00). Pre-trial sleep, diet, and physical activity were standardised, and circadian phenotype was characterised using the Composite Morningness Questionnaire and 7-day actigraphy. RESULTS Mean power, peak power, and distance covered were all significantly higher in the evening compared with morning (p < 0.01). Chronotype (r = - 0.47, p = 0.019) and sleep midpoint (r = 0.52, p = 0.003) were significantly associated with the magnitude of the diurnal performance difference, accounting for 22% and 27% of the variance, respectively. Heart rate, blood lactate, and perceived exertion responses were similar between conditions, indicating comparable physiological strain. Core temperature was higher in the evening (p = 0.026), but did not explain performance differences. CONCLUSIONS These findings demonstrate that endurance exercise performance is enhanced in the evening compared with the morning and suggest that behavioural markers of circadian phenotype are associated with the magnitude of diurnal variation in performance. Time-of-day and circadian phenotype should therefore be considered when optimising exercise testing and prescription.

Melatonin Amplitude, but Not Phase, Is Associated with Sleep Efficiency in the Arctic

Impact of Human Melanopsin Gene (OPN4) Polymorphisms (I394T, P10L) on Nocturnal Melatonin and Daily Rhythms in Young Adults

The findings suggest that I394T‐C carriers exhibit features of the circadian phenotype commonly observed in older cohorts, including reduced rhythm robustness and lower melatonin levels, and support a role for this variant in interindividual differences in light sensitivity and circadian function.

Circadian rhythms in the wild: Skin temperature versus actimetry for short-term field assessment in varying sleep conditions.

Estimating circadian rhythms often relies on intrusive and costly methods like melatonin sampling, misfitting in longitudinal field studies. Alternatively, ambulatory activity monitoring is frequently used, yet requires week-long data and signals fitting poorly with cosinor models. Ambulatory skin temperature monitoring is promising, but its feasibility, reliability, and robustness to homeostatic sleep pressure remain understudied. We collected sensor data in a randomized crossover field study manipulating sleep duration (8 h vs. 4 h time-in-bed, three consecutive nights) among 17 healthy participants (19-32 years old). Activity and skin temperatures (distal, proximal, distal-proximal gradient) were continuously monitored across conditions. Cosinor analysis estimated rhythm parameters (amplitude, mesor, acrophase) and goodness of fit. Non-parametric tests and linear mixed-effect models assessed difference and stability across sleep conditions. Cosinor models fitted better on skin temperature than activity-based data. Sleep restriction affected activity rhythms (reduced amplitude, delayed acrophase, increased mesor). Beside a reduced distal temperature amplitude in sleep restriction, skin temperature rhythm showed no statistically significant moderations by sleep. Rhythm parameters between data types did not significantly correlate. Skin temperature showed promising feasibility for in-field circadian rhythm estimation after only three days, potentially facilitating research on circadian rhythms and health. Validation against core body temperature and melatonin sampling is warranted.

Afternoon exercise was associated with greater fat loss than morning exercise in overweight/obese adults: an exploratory study of PER3 rs228697 genotype matching

Objective Exercise timing may influence metabolic responses and body composition, but the extent to which circadian genetic variation contributes remains unclear. The PER3 rs228697 polymorphism has been linked to chronotype-related traits, although its relevance to exercise timing remains uncertain. This exploratory study examined whether body-composition responses to morning versus afternoon moderate-intensity continuous training (MICT) differed according to PER3 rs228697 genotype in overweight/obese university students. Methods In this 8-week supervised intervention, 31 overweight/obese university students performed MICT in the morning (7:00–10:00) or afternoon (16:00–19:00). Participants with the CC genotype were allocated to a morning training group (CC-AM) or an afternoon training group (CC-PM), and G-allele carriers were included in an afternoon group (G-PM). Body weight, body mass index (BMI), waist circumference, body fat percentage, total fat mass, and regional fat mass were assessed before and after the intervention. Circadian preference, physical activity, sleep quality, and fatigue were also evaluated. Because the G-PM subgroup was very small, findings for this subgroup were treated as exploratory. Results Across the overall sample, body weight, BMI, waist circumference, body fat percentage, and total fat mass decreased over the 8-week intervention. In descriptive subgroup analyses, the CC-PM group showed larger reductions in several body-composition outcomes, including body weight, BMI, waist circumference, body fat percentage, and total fat mass, than the CC-AM group. A similar pattern was observed for several regional fat measures, particularly trunk, android, and gynoid fat mass. By contrast, findings for G-allele carriers were difficult to interpret because of the very small subgroup size. Estimated between-group differences were generally modest and imprecise, and behavioral chronotype did not clearly correspond with PER3 genotype. Conclusions In this exploratory sample of overweight/obese university students, 8 weeks of MICT was associated with favorable changes in several body-composition outcomes. Among CC genotype carriers, afternoon training was associated with descriptively greater improvements than morning training; however, the estimates were imprecise and do not support strong conclusions regarding genotype-based exercise-time matching based on PER3 rs228697 alone. Larger, well-controlled studies with objective circadian phenotyping are needed to clarify the potential role of genotype-informed exercise timing in personalized weight management.