What to watch with Vitamin D 25-OH and Haut?

The question about vitamin D 25-OH and skin is relevant, but the provided context lacks direct studies on this link. Vitamin D is synthesized in the skin via UVB; serum 25-OH is the standard marker for vitamin D status. In skin conditions like psoriasis or eczema, low 25-OH levels are often observed, but causality is unclear – inflammation may lower vitamin D rather than the reverse. High-dose supplementation carries toxicity risk (hypercalcemia), especially with kidney disease or sarcoidosis. The 'poor converter' genetic claim from some DNA tests is not well-supported; conversion to 25-OH is mediated by liver enzymes with modest genetic influence. Without strong evidence from context, the recommendation is: measure 25-OH, consider individual factors (skin type, sun exposure, medications), and supplement only under medical guidance. Evidence for direct skin-vitamin D interactions is mostly mechanistic or observational.