Vitamin D3 modulates the innate immune response through regulation of the hCAP-18/LL-37 gene expression and cytokine production.

The steroid hormone metabolite of vitamin D3, 1α,25-dihydroxyvitamin D3 (1,25D3), promotes osteogenic activity and regulates calcium and phosphate metabolism, which are actions regarded as classical vitamin D-regulated functions. Besides its role in these processes, 1,25D3 also seems implicated in the host defense against microbial/pro-inflammatory attacks. Low serum levels of vitamin D3 (vitamin D deficiency) are associated with osteoporosis and increased risk of fractures but also inflammatory diseases and their disease progression, presumably via mechanisms associated with 1,25D3-evoked modulation of the innate immune system. 1,25D3 has been reported to modulate many inflammatory responses, suggesting that it regulates multiple transcriptional targets within the inflammatory system.