J Clin Virol. 2011 Mar;50(3):194-200. doi: 10.1016/j.jcv.2010.12.006. Epub 2011 Jan 15.
Beard JA1, Bearden A, Striker R. rtstriker at wisc.edu
Vitamin D has long been recognized as essential to the skeletal system. Newer evidence suggests that it also plays a major role regulating the immune system, perhaps including immune responses to viral infection. Interventional and observational epidemiological studies provide evidence that vitamin D deficiency may confer increased risk of influenza and respiratory tract infection. Vitamin D deficiency is also prevalent among patients with HIV infection. Cell culture experiments support the thesis that vitamin D has direct anti-viral effects particularly against enveloped viruses. Though vitamin D's anti-viral mechanism has not been fully established, it may be linked to vitamin D's ability to up-regulate the anti-microbial peptides LL-37 and human beta defensin 2. Additional studies are necessary to fully elucidate the efficacy and mechanism of vitamin D as an anti-viral agent.
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Although few studies have examined the effects of vitamin D on Hepatitis B infection, a study of 2015 Gambian tuberculosis patients identified a silent T to C base change polymorphism in codon 352 of the VDR that was correlated with significantly lowered rates of persistent Hepatitis B infection and tuberculosis, but not malaria.96 This polymorphism affects vitamin D levels, VDR mRNA stability, and VDR mRNA levels.97-100 The antiHepatitis B response in these patients may be cathelicidin mediated, much like the cathelicidin-mediated anti-tuberculosis response recently described.25
In a Vietnamese dengue study, the same polymorphism was associated with resistance to severe dengue.101 At least one study has demonstrated administration of oral vitamin D3 reduces the severity and length of dengue fever, but the small sample size (n = 5) makes it difficult to draw any robust conclusions.102
A study conducted by Bitetto et al. showed that in immune competent patients 25(OH)D levels of less than 10 ng/ml (25 nmol/l) are significantly associated with poorer response to the standard antiviral hepatitis C therapy of ribavirin and pegylated interferon.103 An earlier study by Petta et al. revealed an association between lower vitamin D levels and failure to clear virus during treatment in chronic hepatitis C patients.104 The same study showed that low vitamin D levels were also associated with liver fibrosis. Therefore, this makes it difficult to determine whether lower vitamin D levels correlate with lower viral clearance or are just a consequence of damaged livers.