Sex and age modulate the relationship between melanopsin-dependent light sensitivity and chronotype

Light, acting primarily via melanopsin-mediated signaling, plays a central role in synchronizing circadian rhythms. Individuals vary markedly in the sensitivity of their circadian system to light. Whether these differences contribute to the interindividual variability in chronotype, a behavioral manifestation of internal circadian timing, is unclear. The aim of this study was to determine the relationship between melanopsin-dependent light sensitivity and chronotype and to assess whether age and sex modulate this association across the general population.

Participants (adults and children aged ≥ 8 years) were recruited in a science museum. Chronotype was determined using the μMCTQ. The post-illumination pupillary response (PIPR) was used as a measure of melanopsin-dependent light sensitivity. The relationship between PIPR and chronotype and their interaction with age and sex were assessed using multiple linear regression.

Pupil recordings and questionnaires were obtained from 433 participants, including 269 adults (age range: 18-75 years) and 164 children (age range: 8-17 years). In adults, the relationship between melanopsin-dependent light sensitivity and chronotype depends on sex and age: greater light sensitivity is linked to a significantly later chronotype in young adult men and to an earlier chronotype in older adult women. In children, no evidence was found for a relationship between light sensitivity and chronotype.

Individual variation in light sensitivity interacts with sex- and age-specific differences in the circadian system and light exposure behavior to influence circadian timing. Light exposure recommendations should be personalized to take into account these sex- and age-specific effects.