Observational studies have suggested that vitamin D supplementation could lower the odds of developing respiratory infections, but randomized trials have had mixed results.
Although vitamin D supplementation has been researched and debated for years, the coronavirus disease 2019 (COVID-19) pandemic has escalated the discussion again.
Researchers have known that groups traditionally exhibiting vitamin D deficiency are the same groups that have been disproportionately affected by COVID-19, including older adults and nursing home residents, and Black, Asian, and minority ethnic groups. It has also been clear that increased time spent indoors during the pandemic has limited people’s chances to obtain physiological levels of vitamin D from sunlight.
A report from the National Institute for Health and Care Excellence (NICE) released in December 2020 reviewed recent studies on vitamin D and COVID-19. The recommendations support current recommendations for individuals to supplement vitamin D to maintain bone and muscle health during fall and winter months, but the review concluded that evidence supporting the use of vitamin D for COVID-19 prevention is still lacking.
The longstanding debate around vitamin D began in the 1920s when researchers discovered that it prevented rickets. Investigators began researching its potential uses in non-skeletal outcomes, including immune function, cardiovascular health, and cancer. However, despite clear evidence on the benefits of vitamin D in bone growth and maintenance, evidence supporting the supplementation in other health and disease processes remains lacking.
Notably, observational studies have suggested that vitamin D supplementation could lower the odds of developing respiratory infections, a finding that could have implications in the COVID-19 pandemic; however, randomized trials have had mixed results.
A prespecified analysis from a randomized clinical trial in more than 20,000 Australian adults found that monthly doses of vitamin D did not reduce the risk or severity of acute respiratory tract infections. Although the results did show a statistically significant effect on the overall duration of symptoms based on analysis of participants’ diary data, the reduction was just 0 to 5 days and unlikely to be clinically meaningful.
Similarly, a systematic review and meta-analysis based on aggregate data from trials concluded that vitamin D supplementation was safe and had a small effect on protection from acute respiratory tract infections. This effect was associated with daily doses of between 400 and 1000 IU of vitamin D for up to 12 months, although the investigators noted significant heterogeneity across trials.
The NICE report concluded that it is important to continue monitoring new evidence as it is peer-reviewed and published, including results from several ongoing clinical trials investigating vitamin D and COVID-19 outcomes. Although health decisions should ideally be based on clear evidence, the crisis of COVID-19 may require different rules.
Vitamin D and COVID-19: why the controversy? The Lancet Diabetes and Endocrinology; January 11, 2021. https://www.thelancet.com/journals/landia/article/PIIS2213-8587(21)00003-6/fulltext#articleInformation. Accessed January 21, 2021.