In April 2020 researchers from the USA published their review on the role of vitamin D in reducing the risk of respiratory tract infection, epidemiology of influenza and COVID-19, and how vitamin D supplementation may be a useful measure to reduce risk. Through several mechanisms, vitamin D is able to reduce the risk of infections by lowering viral replication rates and reducing the level of pro-inflammatory cytokines which causes the inflammation that injures the lining of the lungs and leads to pneumonia. These mechanisms can also increase the level of anti-inflammatory cytokines. Whilst several studies have reported that vitamin D supplementation can reduce the risk of influenza, others studies have not. Evidence which supports vitamin D being able to reduce the risk of COVID-19 includes (1) the outbreak occurred during wintertime when an individual’s vitamin D levels are at their lowest; (2) the fact that the number of cases seen in the Southern Hemisphere, which is near the end of summer, are low; (3) that vitamin D deficiency has been found to contribute to acute respiratory distress syndrome; and (4) that case-fatality rates increase with age and when there are underlying chronic diseases, both of which are associated with lower vitamin D levels. To reduce the risk of infection, it is therefore recommended that individuals at risk of influenza and/or COVID-19 consider taking 10,000 IU/d of vitamin D3 for a few weeks to rapidly raise their vitamin D levels, followed by 5000 IU/d. The goal should be to raise vitamin D levels above 40-60 ng/mL (100-150 nmol/L). For treatment of people who become infected with COVID-19, higher vitamin D3 doses may also be useful. Studies should be conducted to evaluate these recommendations.
Grant WB et al. Evidence that Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Deaths. Nutrients. 2020 Apr 2;12(4). pii: E988.