Regardless of whether vitamin D protects against COVID-19, adequate levels are important for bone health. “Avoiding vitamin D deficiency is always a goal,” Ross wrote. “If the diet doesn’t include vitamin D fortified milk or natural products like fish, then a supplement of the RDA [recommended dietary allowance] amount (600-1000 IU per day) provides good assurance. I consider this a ‘good idea,’ but I don’t want to leave the impression that diet cannot be sufficient.”

In this single-center, retrospective cohort study, likely deficient vitamin D status was associated with increased COVID-19 risk, a finding that suggests that randomized trials may be needed to determine whether vitamin D affects COVID-19 risk.