Sunlight and Vitamin D Production in the Body
Sunlight plays a unique role in vitamin D physiology because it enables the body to produce vitamin D directly in the skin. When skin is exposed to ultraviolet B (UVB) radiation, a compound in the skin is converted into vitamin D, initiating the pathway that leads to activation and biological signalling.
This process is influenced by multiple variables, including the intensity of sunlight, duration of exposure, skin characteristics, and environmental conditions. Unlike dietary sources, sunlight-driven production is self-limiting and regulated, meaning vitamin D synthesis slows once sufficient levels are reached within the skin.
Because sunlight exposure varies widely between individuals and environments, vitamin D production from sun exposure is inherently variable. This variability contributes to differences in vitamin D availability and helps explain why sun exposure alone does not guarantee uniform vitamin D status or response.
Understanding the relationship between sunlight and vitamin D helps clarify why vitamin D physiology cannot be reduced to a single source or behaviour. Sun-driven production operates within biological limits and environmental constraints.
This page focuses on sunlight as one pathway for vitamin D production. Later sections explore how factors such as geography, season, skin physiology, and lifestyle influence the contribution of sunlight to overall vitamin D handling in the body.