Disrupted daily rhythms in light exposure and wrist temperature are associated with metabolic risk markers and...

Light exposure is the primary external synchronizer of the body's internal clocks and daily rhythms. This study investigated whether light exposure and wrist temperature real-life 24-h rhythms are associated with obesity and metabolic risk markers in a large cohort of healthy adults.

A total of 809 individuals from the ONTIME-MT study (ClinicalTrials.gov NCT03036592) were included. Mean age was 37.47 ± 14.24 years, mean BMI was 25.75 kg/m², and 71% were women. Daily light exposure and wrist temperature were continuously monitored over seven consecutive days under free-living conditions. Principal component analysis was used to identify factors capturing circadian-related functioning.

Cross-sectional study.

Healthy adults of European descent from a Spanish cohort assessed in an ambulatory setting.

Obesity-related and metabolic risk parameters.

Three factors emerged in both the light exposure and wrist temperature rhythm domains, explaining approximately 73% and 80% of the total variance. In both domains, Factor 1 accounted for the largest proportion of variance (≈41-42%) and reflected overall rhythm robustness, characterized by higher relative amplitude and greater interdaily stability, together with average light exposure or wrist temperature levels. Higher light exposure Factor 1 was associated with lower serum triglyceride concentrations (P = 0.013). Wrist temperature Factor 1 was associated with lower BMI and body fat percentage in women, as well as lower insulin, HOMA-IR and triglyceride levels, and higher HDL-cholesterol (all P < 0.05). Mediation analyses showed that interdaily stability of wrist temperature rhythms may affect the association between light exposure stability and triglyceride levels, accounting for approximately 11% of the total effect (P = 0.021).

In this large real-life cohort, less robust daily rhythms of light exposure and wrist temperature were consistently associated with adverse metabolic profiles. These findings highlight the potential of circadian-related markers derived from wearable technologies as non-invasive indicators of metabolic risk.

ONTIME-MT study; ClinicalTrials.gov NCT03036592.