Low vitamin D status in winter permits viral epidemics. During winter, people who do not take vitamin D supplements are likely to have low serum 25-hydroxyvitamin D [25(OH)D] concentrations
Vitamin D can reduce the risk of viral epidemics and pandemics in several ways. First, higher 25(OH)D concentrations reduce the risk of many chronic diseases, including cancers, cardiovascular disease, chronic respiratory tract infections (RTIs), diabetes mellitus, and hypertension. Patients with chronic diseases have significantly higher risk of death from RTIs than otherwise healthy people