Melatonin suppression by light involves different retinal photoreceptors in young and older adults
IntroductionAge-related sleep and circadian rhythm disturbances may be due to altered non-visual photoreception. Here, we investigated the temporal dynamics of light-induced melatonin suppression in young and older individuals. MethodsIn a within-subject design study, young and older participants were exposed for 60 minutes (0030-0130 at night) to 9 narrow-band lights (range: 420 to 620 nm). Plasma melatonin suppression was calculated at 15, 30, 45, and 60 min time intervals. Individual spectral sensitivity of melatonin suppression and photoreceptor contribution were predicted for each interval and age group. ResultsIn young participants, melanopsin solely drove melatonin suppression at all time intervals, with an invariant peak sensitivity at [~]485 nm established only after 15 minutes of light exposure. Conversely, in older participants, spectral light-driven melatonin suppression was best explained by a model combining melanopsin + L-cones with a stable peak sensitivity ([~]499 nm) at 30, 45, and 60 minutes of light exposure. ConclusionAging is associated with a distinct photoreceptor contribution to melatonin suppression by light. While in young adults melanopsin-only photoreception is a reliable predictor of melatonin suppression, in older individuals this process is jointly driven by melanopsin and L-cones. These findings offer new prospects for customizing light therapy for older individuals.