A patient with pemphigus vulgaris asks which vitamin supplement could potentially worsen their condition if taken in excess. Which vitamin is most relevant?

Pemphigus vulgaris (PV) is an autoimmune blistering disease driven by autoantibodies against desmoglein 3, causing intraepithelial blistering. Vitamin E at high doses has immunomodulatory and potentially pro-inflammatory effects that may upregulate immune responses, potentially exacerbating autoimmune activity. High-dose Vitamin E has been associated with disease flares in autoimmune conditions and has shown pro-oxidant effects at supraphysiologic doses. In contrast, Vitamin D deficiency is COMMON in PV and correlates with disease severity — maintaining adequate Vitamin D is actually beneficial. Vitamins B3 and B12 are water-soluble and excreted; Vitamin C is also water-soluble and not linked to PV exacerbation. The clinically significant answer for worsening PV through excess supplementation is Vitamin E.