Vitamin D supplements do nothing to protect against respiratory infections, studies reveal

LONDON — Buying vitamin D or fish oil supplements is a waste of money, if you’re hoping they’ll protect you from contracting COVID-19, a pair of new studies conclude.

Researchers in both the United Kingdom and Norway have found that taking vitamin D or cod liver oil has no noticeable impact on someone’s risk for contracting COVID or any other respiratory tract infection.

Vitamin D metabolites have a reputation for supporting the human immune system and its response against respiratory viruses and bacteria. Previous studies have suggested that taking vitamin D supplements can help protect against these illnesses, especially if the person has a vitamin D deficiency. There has been recent speculation that vitamin D could prevent or even treat cases of COVID-19. However, these studies have produced mixed results with no definitive proof.

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What did new the studies on vitamin D find?

The first trial involved 6,200 participants over the age of 16 who were not taking vitamin D supplements at the start of the study in December 2020. Half of them took a vitamin D blood test with 86 percent (2,674) discovering they had a vitamin D deficiency. These participants received either 3200 IU/day or 800 IU/day of vitamin D supplements for six months, with the rest of the study group did not take any supplements.

After six months of follow-up, study authors found that neither dosage of vitamin D led to any impact on the rates of acute respiratory tract infections or COVID-19 during that time. The number of adverse events and illnesses was similar between all groups in this experiment.

In the second trial, between November 2020 and June 2021, 34,741 adults in Norway took either a 5-mL cod liver oil supplement or a placebo for six months. All of these participants were not taking vitamin D or fish oil supplements before the experiment. Unlike the previous trial, 86 percent of the Norwegian participants had adequate vitamin D levels at the start of the study.

Results again revealed that taking cod liver oil supplements did not lower the rates of acute respiratory infections or COVID-19 in comparison to people taking a placebo. Cod liver oil contains low levels of vitamin D as well as vitamin A and omega-3 fatty acids.

“Together, these new results suggest that vitamin D supplements do not reduce risk of COVID-19 or other acute respiratory infections,” researchers report in a media release.

Professor Peter Bergman from the Karolinska Institutet in Sweden adds that COVID vaccines are still the most effective way of protecting yourself against COVID. The professor notes that people with normal vitamin D levels should also avoid taking either of these supplements.

The findings are published in The BMJ.

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