Vitamin D has been one of the most commonly purchased supplements for immunity since the beginning of the COVID-19 pandemic, and there have been varying accounts of how strong the evidence is for vitamin D’s role in preventing infection. The Scientific Advisory Committee on Nutrition (SACN) and National Institute for Health and Care Excellence (NICE) recently reviewed the published evidence on the role of high doses of vitamin D supplementation in preventing COVID-19.
The main finding from both reviews is that there is currently no evidence to support taking vitamin D supplements above and beyond the daily recommendation specifically to prevent or treat COVID-19. This is partly due to a lack of studies done specifically on vitamin D and COVID-19.
However, vitamin D supplementation could have health benefits for those who are vitamin D deficient, which is very common in countries in the northern hemisphere. Few people meet their daily vitamin D requirement of 10-15 micrograms per day, depending on global region,
Highlights of the NICE review include:
Evidence was from 5 published studies in peer-reviewed journals. One observational cohort study (D’Avolio et al. 2020), 3 observational prognostic studies involving published data sets using correlation or regression (Hastie et al. 2020, Ilie et al. 2020 and Laird et al. 2020) and 1 case-control survey (Fasano et al. 2020) looked retrospectively at the association between vitamin D status and development of COVID‑19. None of the studies were intervention trials of vitamin D supplementation for the prevention or treatment of COVID‑19.
Four of the studies found an association or correlation between a lower vitamin D status and subsequent development of COVID‑19. However, confounders such as body mass index (BMI) or underlying health conditions, which may have independent correlations with vitamin D status or COVID‑19, were not adjusted for (D’Avolio et al. 2020, Fasano et al. 2020, Ilie et al. 2020 and Laird et al. 2020). Vitamin D status was based on serum 25‑hydroxyvitamin D (25(OH)D) levels in 3 studies and the proportion of participants taking a vitamin D supplement in 1 study. The largest UK study (Hastie et al. 2020) found an association between vitamin D status and COVID‑19 only in a univariable analysis (with this single potential causative factor). Importantly, no causal relationship between vitamin D status and COVID‑19 was found after adjustment for confounders such as comorbidity, socio-demographics, ethnicity, BMI and other baseline factors.
A person’s individual risk of vitamin D deficiency may have changed during the COVID-19 pandemic, particularly if they are spending more time indoors. Sunlight is the major source of vitamin D for most people, therefore vitamin D status will be influenced by sunlight exposure. People from ethnic minority groups with dark skin are also at particular risk of having a low vitamin D status.
For most people, 10 micrograms of vitamin D a day will be enough and people should not take more than 100 micrograms a day because it could be harmful. If people take higher therapeutic doses of vitamin D, monitoring is recommended.
You can read the full summary of the evidence reviews on the British Nutrition Foundation website here.