This study doesn't involve XMRV, but that other retrovirus HIV, so I thought perhaps it might be worth posting... J Infect Dis. 2009 Oct 1;200(7):1022-30. Perinatal outcomes, including mother-to-child transmission of HIV, and child mortality and their association with maternal vitamin D status in Tanzania. Abstract BACKGROUND: Vitamin D is a strong immunomodulator and may protect against adverse pregnancy outcomes, mother-to-child transmission (MTCT) of human immunodeficiency virus (HIV), and child mortality. METHODS: A total of 884 HIV-infected pregnant women who were participating in a vitamin supplementation trial in Tanzania were monitored to assess pregnancy outcomes and child mortality. The association of these outcomes with maternal vitamin D status at enrollment was examined in an observational analysis. RESULTS: No association was observed between maternal vitamin D status and adverse pregnancy outcomes, including low birth weight and preterm birth. In multivariate models, a low maternal vitamin D level (<32 ng/mL) was associated with a 50% higher risk (95% confidence interval [CI], 2%-120%) of MTCT of HIV at 6 weeks, a 2-fold higher risk of MTCT of HIV through breast-feeding among children who were HIV uninfected at 6 weeks (95% CI, 1.08-3.82), and a 46% higher overall risk of HIV infection (95% CI, 11%-91%). Children born to women with a low vitamin D level had a 61% higher risk of dying during follow-up (95% CI, 25%-107%). CONCLUSIONS: If found to be efficacious in randomized trials, vitamin D supplementation could prove to be an inexpensive method of reducing the burden of HIV infection and death among children, particularly in resource-limited settings. http://www.ncbi.nlm.nih.gov/pubmed/19673647 If vitamin D can reduce HIV replication/transmission -- perhaps it would help with XMRV?