P175 Sunlight exposure, vitamin D benefit and DNA damage harm: a systematic review of human experimental studies across skin phototypes

Abstract

Skin solar ultraviolet radiation (UVR) exposure is a major source of vitamin D synthesis, but UVR concurrently causes skin DNA damage, which may contribute to skin cancer risk. The relationship between these beneficial and hazardous effects may vary by skin phototype. This study aimed to examine the relationship between the vitamin D (UVR-benefit) and skin DNA damage (UVR-harm) concurrently produced following UVR exposure, and to evaluate how this relationship differs across skin phototypes. A systematic review was performed in accordance with the PRISMA guidelines to identify human intervention studies reporting both changes in serum 25-hydroxyvitamin D levels and markers of skin DNA damage following UVR exposure. Literature searches were performed on 26 January 2025 across four databases (PubMed, MEDLINE OVID, MEDLINE Embase and Scopus). Studies were appraised using the National Heart, Lung and Blood Institute quality assessment tools. The findings were synthesized narratively and summarized in tables to inform evidence-based sun-exposure recommendations. The PROSPERO registration number for this study is CRD42025625834. Four studies, comprising data from 158 participants, were included. All studies were assessed as having fair-to-good quality. Two studies on solar-simulated radiation explored the effects of low-level exposure, while two sunlight studies explored the effects of high-level exposures, on 25-hydro­xy­vitamin D gain and cyclobutane pyrimidine dimer (CPD) formation. UVR exposure benefited vitamin D status and generated CPDs across all phototypes. Individuals with darker skin required higher exposure to achieve vitamin D sufficiency, with CPD formation not detected in basal (dividing) epidermal cells where epidermal localization was assessed. In contrast, individuals with the lightest skin phenotypes did not achieve vitamin D gains without concurrent basal cell CPD formation. These findings demonstrate phototype-specific differences in the balance between vitamin D benefit and UVR-induced DNA damage, which have implications for personalized sun-exposure guidance and the role of vitamin D supplementation.