Is Sunlight a Vitamin or a Hormone?

Logosofia no Dia a Dia · May 8, 2026 · 34m

We all know the advice: take your vitamin D, avoid too much sun. But what if that framing is fundamentally wrong? In this episode, we explore a provocative question from listener Daniel: why do we still call it a vitamin when it functions as a secosteroid hormone, produced in the skin through sun exposure? We trace the history of the "vitamin" label back to the 1920s and unpack how vitamin D receptors are expressed in nearly every tissue in the body—from immune cells to the brain. Then we go further, examining the separate pathways through which sunlight affects health, including nitric oxide…