  Coronavirus disease 2019 (COVID-19) has caused global disruption and a
significant loss of life. Existing treatments that can be repurposed as
prophylactic and therapeutic agents could reduce the pandemic's devastation.
Emerging evidence of potential applications in other therapeutic contexts has
led to the investigation of dietary supplements and nutraceuticals for
COVID-19. Such products include vitamin C, vitamin D, omega 3 polyunsaturated
fatty acids, probiotics, and zinc, all of which are currently under clinical
investigation. In this review, we critically appraise the evidence surrounding
dietary supplements and nutraceuticals for the prophylaxis and treatment of
COVID-19. Overall, further study is required before evidence-based
recommendations can be formulated, but nutritional status plays a significant
role in patient outcomes, and these products could help alleviate deficiencies.
For example, evidence indicates that vitamin D deficiency may be associated
with greater incidence of infection and severity of COVID-19, suggesting that
vitamin D supplementation may hold prophylactic or therapeutic value. A growing
number of scientific organizations are now considering recommending vitamin D
supplementation to those at high risk of COVID-19. Because research in vitamin
D and other nutraceuticals and supplements is preliminary, here we evaluate the
extent to which these nutraceutical and dietary supplements hold potential in
the COVID-19 crisis.
