evidence: An analysis of data from 4962 participants in the National Health and Nutrition Examination Survey found that 1981 (39.92%) were vitamin D deficient, defined as a blood level lower than 20 ng/mL (<50 nmol/L). Vitamin D deficiency was greater in certain subpopulations, such as people with obesity or with type 1 or type 2 diabetes—all 3 of which have been associated with worse COVID-19 outcomes. [...] On the other hand, a study in a northern Italy hospital found no association between vitamin D and COVID-19. In a review article published in a different journal the same day as their study, the researchers in Italy concluded that poor vitamin D status appears to be linked to an increased risk of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, but age, sex, and comorbidities seem to play a more important role in COVID-19 severity and mortality. Nine days later, a different group of Italian researchers published an observational study of 324 patients with COVID-19 that found taking vitamin D supplements was not linked to risk of hospitalization but was associated with a higher risk of dying if hospitalized. [...] The authors focused on an Indonesian retrospective study linking low vitamin D levels to a higher risk of dying from COVID-19. Although the publication had not been peer-reviewed, "it has taken the internet by storm," garnering thousands of tweets, not to mention headlines in major news outlets, the letter writers noted.