Season of birth has been largely studied in the context of the life-course perspective on mental health.
In our study performed on a sample of more than 70,000 middle-aged and older Europeans, we observed that season of birth had virtually no effect on symptoms of depression and anxiety. While having been a topic of study for decades, the relationship between season of birth and risk for depression and anxiety over the life-course has previously lacked large-scale generalizable evidence. Previous studies have suggested an effect of season of birth on several mental health outcomes, with the most consistent association found for being born in winter and increased risk for mental disorders. These associations were primarily explained by varying exposures during the perinatal period related to viral infections, climate influences, nutritional deficiences, differences in sunlight or levels of vitamin D.
Taking into consideration the strong evidence-base indicating nutrition and disease exposure as predictors of mental health over the life-course, and the present results indicating no association between season of birth and symptoms of depression and anxiety, it seems that season of birth as a predictor of mental health currently no longer insufficient. Historically, when season of birth was found significantly associated with mental illness, it was likely successfully acting as a proxy indicator for an unaccounted-for mediating mechanism, which in the current socioeconomic context in Europe no longer exists.
You can read our study published in Scientific Reports here.