Table 1.

Lines of evidence that vitamin D deficiency is an important modifiable risk factor for COVID-19.

• Laboratory studies: Vitamin D is important for immune function, modulates the inflammatory response to infection, and regulates the renin-angiotensin system. • Ecologic studies: Countries with lower average levels of 25(OH)D or lower solar ultraviolet-B radiation exposure have higher COVID-19 mortality. • Demographic groups known to be at higher risk of vitamin D deficiency—Black individuals, the elderly, nursing-home residents, and those with obesity, vascular comorbidities, or chronic kidney disease—are also those at high risk of COVID-19 hospitalization and/or mortality. • Observational studies of individuals tested for SARS-CoV-2a: Low 25(OH)D levels are associated with a greater likelihood of testing positive for the virus. • Observational studies of COVID-19 patients: 25(OH)D levels correlate inversely with COVID-19 severity. • Observational studies (pre-COVID era): Low vitamin D status is associated with increased risk of acute respiratory tract infections. • Randomized clinical trials (pre-COVID era): Vitamin D supplementation decreases risk of respiratory tract infection, especially in those with low 25(OH)D levels.

^aSARS-CoV-2, severe acute respiratory syndrome coronavirus 2.