Abstract
This study examines the causal effects of sunlight exposure on suicide rates. Leveraging county-month-year data on solar insolation and suicide rates in the U.S. from 1979 to 2004, we provide first robust evidence that insufficient sunlight increases suicide rates. We also find that insufficient sunlight increases Google searches containing depressive language, suggesting a potential adverse impact on mental well-being. Importantly, our findings favor a biological pathway over alternative mechanisms. The estimated effect of sunlight on suicide, often exceeding other interventions in magnitude, sheds new light on sunlight as a significant risk factor in suicide incidence.