STUDY OBJECTIVES: Light, acting primarily via melanopsin-mediated signaling, plays a central role in synchronising 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 behavioural 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.
METHODS: 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.
RESULTS: 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.
CONCLUSION: Individual variation in light sensitivity interacts with sex- and age-specific differences in the circadian system and light exposure behaviour to influence circadian timing. Light exposure recommendations should be personalised to take into account these sex- and age-specific effects.
