Genetics

A large Mendelian randomization study used vitamin D–associated genetic variants to investigate whether low circulating 25-hydroxyvitamin D contributes causally to multiple sclerosis. The findings showed that a genetically predicted one-standard-deviation decrease in vitamin D was associated with approximately twice the odds of MS, with the association remaining significant across several sensitivity analyses. Although the results strengthen the case that long-term vitamin D insufficiency may influence MS susceptibility, they do not prove that supplementation can prevent or treat the disease. Long-term randomized controlled trials are still needed to translate this genetic evidence into clinical recommendations.