It is widely accepted that climate and season have an effect on psychological traits(1,2). General mood and mood disorders such as depression, anxiety, bipolar disorder and particularly, seasonal affective disorder, have been shown to vary with seasonality, weather, latitude and exposure to sunlight(3–7). For instance, in summer mania admissions and suicidal behaviour were reported to be higher(8,9) and depressive episodes less frequent(8). Whilst direct and indirect sunlight was found to influence the sleep cycle, anxiety and depressed mood(4).Biological explanations for this relationship involve neurotransmitter regulation and vitamin D synthesis. Sunlight exposure on the retina stimulates intrinsically sensitive retinal ganglion cells, and as a consequence the secretion of melatonin, which is critical for regulating the sleep-wake cycle (circadian rhythm). Sunlight also plays a role in the production of serotonin, a neurotransmitter that elevates mood, whereas bright light affects endocrine and neurophysiological responses in the brain that trigger alertness(4). Additionally, sun exposure is the main source of the hormone vitamin D, which exerts its biological effects throughout the body (at least 36 human tissues have been found to contain vitamin D responsive elements, including the brain)(7). Vitamin D deficiency has been associated with mental disorders and increased depressive symptoms in a range of populations, as well as with poorer cognitive performance(5,10). In an earlier study carried out in ALSPAC children we generated polygenic scores, using polymorphisms in pigmentation genes, that were strongly associated with the participant’s pigmentation characteristics and in turn with their reaction to the sun and use of sun protection(11). In this new study we would like to explore the potential association of similar polygenic scores –as proxies for sun exposure- with mental health problems experienced by ALSPAC now young adults and their mothers.

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