Two studies demonstrate that vitamin D supplements do not protect against COVID-19 disease and other acute respiratory tract infections.
The first study was conducted in the United Kingdom and included 6,200 participants aged 16 and older who were not taking vitamin D supplements. Of those, 3,100 people were found to have low vitamin D levels.
Vitamin D deficient participants were then randomized into two groups: the first group took 800 IU of vitamin D supplement every day, whereas the second group consumed 3,200 IU of vitamin D daily. Participants with sufficient vitamin D levels served as controls.
Overall, 299 participants experienced at least one episode of swab test confirmed or doctor-confirmed acute respiratory tract infection. In the group taking the lower dose, 5,7% of participants got infected, and the proportion among those consuming the higher dose was 5.0%. In the control group, 4.6% of participants had confirmed infection.
The authors concluded that taking supplements either in smaller or larger doses “is not associated with a reduction in risk of all-cause acute respiratory tract infection or COVID-19.”
Another study was carried out in Norway from November 2020 to June 2021. Research enrolled 34 601 adults aged 18-75 years, most of which (75%) did not use vitamin D supplements before the trial.
The first group of participants took 5 milliliters (one teaspoon) of cold liver oil containing about 400 IU of vitamin D daily. The placebo group took a teaspoon of corn oil.
In total, 455 participants had a positive SARS-CoV-2 test result, with similar event rates in the cod liver oil and placebo groups, 227 and 228, respectively.
“Supplementation with cod liver oil in the winter did not reduce the incidence of SARS-CoV-2 infection, serious covid-19, or other acute respiratory infections compared with placebo,” the authors conclude.
Both studies were published in the British Medical Journal.
According to the National Institutes of Health (NIH), the recommended daily vitamin D intake for children and adults from 1 to 70 years old is 600 IU. For adults 71 years and older, the recommended dose is 800 IU.