The diverse immunomodulatory effects of vitamin D are increasingly being recognized. However, the ability of oral vitamin D to modulate acute inflammation in vivo has not been established in humans. In a double-blinded, placebo-controlled interventional trial, twenty healthy adults were randomized to receive either placebo or a high dose of vitamin D3 (cholecalciferol) one hour after experimental sunburn induced by an erythemogenic dose of ultraviolet radiation. Compared to placebo, participants receiving vitamin D3 (200,000 IU) demonstrated reduced expression of pro-inflammatory mediators TNF-α (p=0.04) and iNOS (p=0.02) in skin biopsy specimens 48 hours after experimental sunburn. A blinded, unsupervised hierarchical clustering of participants based on global gene expression profiles revealed that participants with significantly higher serum vitamin D3 levels after treatment (p=0.007) demonstrated increased skin expression of the anti-inflammatory mediator arginase-1 (p=0.005), and a sustained reduction in skin redness (p=0.02), correlating with significant expression of genes related to skin barrier repair. In contrast, participants with lower serum vitamin D3 levels had significant expression of pro-inflammatory genes. Together the data may have broad implications for the immunotherapeutic properties of vitamin D in skin homeostasis, and implicate arginase-1 up regulation as a previously unreported mechanism by which vitamin D exerts anti-inflammatory effects in humans.
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