Since the onset of the COVID-19 pandemic, there has been a proliferation of human clinical trials aiming to evaluate the potential role that vitamin D concentrations have in the infection rates and overall outcomes in patients affected by the virus.
 
Via its consumer education initiative, the Council for Responsible Nutrition (CRN) has presented 13 meta-analyses on the vitamin D and COVID-19 front, via its “Vitamin D and Me!” consumer education campaign. The website shares research, expert video interviews, news, and education in a user-friendly format, with a particular focus on U.S. consumers aged 55 and up, and has already brought over 160,000 visitors.
 
Across these systematic reviews, vitamin D blood concentrations appear to have a direct correlation with lowered incidences and severity of COVID-19 in most but not all of the research reviews.
 
“Increasing evidence suggests a link between higher vitamin D levels and lower incidence of COVID-19,” Luke Huber, ND, MBA, vice president of scientific and regulatory affairs at CRN, said. “We have known for years that vitamin D plays an important role in immune health, and now there are multiple meta-analyses that appear to demonstrate the benefits of this nutrient in COVID-19.”
 
The 13 recent meta-analyses were generated from more than 100 clinical trials published since the onset of the pandemic, most of which examined blood concentrations of vitamin D while two exclusively examined vitamin D consumption in relation to the disease.
 
Most of the reviews found direct correlations between vitamin D and lowered incidence of COVID-19, and several but not all meta-analyses found that more severe cases of COVID-19 and mortality were linked with lower vitamin D levels. One meta-analysis found reduced mortality with vitamin D intervention following COVID-19 diagnosis, while a smaller meta-analysis did not find a statistically significant relationship, with the two key differences between these reviews being timing and dosages.
 
“Consumers need science-based evidence to make informed health decisions,” Brian Wommack, executive director of the CRN Foundation, said. “We hope consumers use these findings to better understand how nutrients like vitamin D support their goal of living a healthy lifestyle.”
 
“This growing body of research does not indicate that vitamin D is a substitute for vaccines, mask wearing, social distancing, or other behaviors to mitigate the spread of the coronavirus,” Huber said, “but the data does suggest that vitamin D levels may play a role, in combination with other therapies, in strengthening the immune system to resist the virus.”
 
The meta-analyses included:
 
- “Association of vitamin D deficiency with COVID-19 infection severity: Systemic review and meta-analysis,” (Wang Z et. al, Clin Endocrinol, 2021), a review of 17 observational studies with 2,756 eligible adult patients which linked vitamin D deficiency to greater severity of COVID-19 infection.
 
- “A systematic review and meta-analysis of effect of vitamin D levels on the incidence of COVID-19,” (Szarpak L et al., Cardiology, 2021), a review which connected vitamin D blood status and COVID-19 infection rates. The study found that mean vitamin D levels in COVID-19 negative pateints was 17.7 ± 6.9 ng/mL compared to positive patients who had 14.1  ± 8.2 ng/mL across a population of 14,485 participants.
 
- “The Impact of Vitamin D Level on COVID-19 Infection: Systematic Review and Meta-Analysis,” (Teshome A et al., Frontiers in Public Health, 2021), a meta-analysis of 14 studies which found that, on average, people with deficiencies in vitamin D were 80% more likely to acquire COVID-19 than those who had normal levels of vitamin D. The data was sourced from 14 studies with a pool of 91,120 participants.
 
- “Vitamin D Deficiency aggravates COVID-19: systematic review and meta-analysis,” (Pereira M et al., Crit Rev Food Sci Nutr, 2021), a review which utilized 26 studies sourced from 8,176 COVID-19 patients with a mean age of 58 years, which reported a positive association between vitamin D deficiency and COVID-19 severity.
 
- “Association of Vitamin D Status with SARS-CoV-2 Infection or COVID-19 Severity: A Systematic Review and Meta-Analysis,” (Kazemi A et al., Advances in Nutrition, 2021) a meta-analysis sourced from 39 studies which found significant associations between 25(OH)D blood concentrations and both risk of COVID-19 infection and severe outcomes including death.
 
- “Low Vitamin D Status is associated with coronavirus disease 2019 outcomes: a systematic review and meta-analysis,” (Liu N et al., International Journal of Infectious Diseases, 2021), a meta-analysis which found that both low vitamin D status and obesity increased the risk of testing positive for COVID-19. The review comprised ten articles published, which sourced data from 361,934 participants who on average were more likely to become infected with COVID-19 if they had a lower vitamin D level.
 
- “Vitamin D supplementation and clinical outcomes in COVID-19: a systematic review and meta-analysis” (Pal R et al. J Endocrinol Invest., 2021) which assessed clinical outcomes and mortality in 2,933 COVID-19 patients across 13 studies. The review included studies which covered vitamin D supplementation before the diagnosis of COVID-19, and showed that the use of vitamin D supplements (oral cholecalciferol or oral calcifediol) was linked with improved clinical outcomes, though the dosages used in the studies were highly variable.
 
- “The role of vitamin D in the age of COVID-19: A systematic review and meta-analysis,” (Ghasemian R et al., Int J Clin Pract., 2021), which sourced data from 23 studies altogether including 11,901 participants, concluding that low vitamin D status may influence whether or not one becomes infected with COVID-19 and may impact outcomes. In the meta-analysis, 41% of COVID-19 patients were suffering from vitamin D deficiency, and in 42% of patients, vitamin D levels were lower than normal range. Only 19% of participants had normal vitamin D levels. The meta-analysis also included other comorbidities such as cancer, chronic kidney disease, cardiovascular diseases, diabetes, hypertension, obesity, respiratory diseases, dementia, and depression/anxiety.
 
- “Low Serum 25-hydroxyvitamin D (Vitamin D) Level Is Associated with Susceptibility to COVID-19, Severity, and Mortality: A Systematic Review and Meta-Analysis,” (Akbar MR et al., Frontiers in Nutrition, 2021), which investigated 14 studies including 999,179 participants to conclude that low 25-OHD concentrations were associated with both higher infection rates and mortality in COVID-19 patients compared to a control group.
 
- “The link between COVID-19 and Vitamin D (VIVID): A systematic review and meta-analysis,” (Bassatne A et al., Metabolism, 2021), a review of 31 observational studies including over 8,209 patients between the ages of 42 and 81. The researchers found positive but not statistically significant trends between 25-OHD levels and COVID-19 mortality, ICU admission, invasive ventilation, non-invasive ventilation, or positivity, though the authors characterized the studies as “largely poor-quality.”
 
- “Influence of 25-hydroxy-cholecalciferol levels on SARS-CoV-2 infection and COVID-19 severity: A systematic review and meta-analysis,” (Crafa A, EClinicalMedicine, 2021), an investigation of 29 studies including adult participants which found that blood concentrations of vitamin D were lower in patients with COVID-19 than negative ones, vitamin D levels were significantly lower in patients with severe disease and those who died, and patients with vitamin D deficiency had an increased risk of developing severe disease but not a fatal outcome.
 
- “Therapeutic and prognostic role of vitamin D for COVID-19 infection: A systematic review and meta-analysis of 43 observational studies,” (Petrelli F et al., J Steroid Biochem Mol Biol., 2021) a systematic review sourcing data from 612,601 patients. A small portion of these studies investigated supplementation, reporting a therapeutic effect on severity and mortality rate.
 
- “Vitamin D supplementation and COVID-19 treatment: A systematic review and meta-analysis,” (Rawat D, et al., Diabetes Metab Syndr., 2021), A review of five studies including 467 patients which found that there was no difference achieved with vitamin D supplementation on major health outcomes in COVID-19.