Question: It seems like Vitamin D is back in the news again. What’s the word?

Answer: Two days ago, JAMA Infectious Diseases published a new observational study, “Association of Vitamin D Status and Other Clinical Characteristics With COVID-19 Test Results” that found statistically significant relationship between Vitamin D deficiency and COVID-19 infection (i.e. testing positive for the virus). These findings point to the need for more robust study — ideally randomized control trials (RCTs). On that front, the good news is that a number of RCTs examining Vitamin D and COVID-19 are already recruiting! Study findings also support the notion that we should be soaking up more sun and taking Vitamin D supplements to help protect against COVID-19 and other respiratory infections (in addition to protecting our bone health). So go on, follow the advice of multiple medical societies by letting some sun shine on your face every day, eating food with Vitamin D (like fatty fish, egg yolks, or foods fortified with D), and/or start taking those daily supplements! Read on for more information on the study’s findings…

We talked about Vitamin D way back in our Q&A of 4/24 (#Vitamin D), and there’s been some research published since then, including this observational study, “Vitamin D concentrations and COVID-19 infection in UK Biobank” that found no relationship between Vitamin D and susceptibility to COVID-19 infection. In contrast, this new study overcame two key limitations of the UK study — 1) it focused on Vit D levels as measured within the period 2 weeks to 12 months before positive COVID test, thereby ensuring temporal consistency (the UK study used Vit D measures from 10–14 years prior); 2) it controlled for Vit D treatment, thereby ensuring that the measure of deficiency was more precise. The new study also controlled for a host of factors, including age, sex, race, ethnicity, body mass, and a host of comorbidities including but not limited to hypertension and diabetes. In so doing, study authors found that patients with likely Vitamin D deficiency “had an increased relative risk of testing positive for COVID-19 (relative risk, 1.77; 95% CI, 1.12–2.81; P = .02) compared with patients with likely sufficient status at the time of COVID-19 testing.” Put another way, this study found that people who are likely Vitamin D deficient have a risk of testing positive for COVID-19 that is 77% higher than the risk of people who are likely Vitamin D sufficient. Now, because of the design of this study and the fact that Vitamin D deficiency could be a consequence associated with other health conditions and behaviors that increase COVID susceptibility, it’s not possible to determine a causative relationship. This is why RCTs are so important. In the meantime, because Vitamin D is safe (as long as you don’t overdo the supplements and you don’t get sunburnt), these findings add to the chorus encouraging us to boost our Vitamin D levels.