Myths vs facts: Vitamin D 25-OH and Haut

Myth: 'More sun equals more vitamin D, so it's always good for the skin.' Fact: Vitamin D synthesis in the skin is efficient but depends on UV index, skin type, age, and latitude. Excessive UV exposure increases skin cancer risk without proportionally raising 25-OH levels – synthesis is self-limiting. Another myth: 'Vitamin D supplements cure all skin conditions.' Fact: There is evidence for topical vitamin D analogs in psoriasis, but for acne, eczema, or anti-aging, robust clinical trials are lacking. The 25-OH blood level is the best marker for vitamin D status; values below 30 nmol/L indicate deficiency. However, routine supplementation without testing is not recommended except for at-risk groups. Consumer DNA tests claiming to predict vitamin D 'genes' have limited clinical utility – environment (sun, diet) is far more influential. Bottom line: Moderate sun exposure, supplement only when needed and under medical guidance. Evidence: strong for synthesis and deficiency, moderate for specific skin therapies.