Link between vitamin D supplements and reduced COVID-19 risk slammed in study

08 Sep 2022 --- Two studies published in the BMJ showed no association between a lowered risk of COVID-19 or respiratory tract infections for adults taking vitamin D supplements. However, there are limitations for both trials as vaccine implementation occurred during the same period.

Previously recognized to support innate immune responses to respiratory viruses and bacteria, vitamin D has received much attention for its role in the COVID-19 pandemic. However, most studies carried out have been observational and shown mixed results.

In December 2020, a study was conducted in the UK, including 6,200 adults. They started consuming supplements at the beginning of the study. Half of the participants were offered supplements and high dosages were given for those with vitamin D deficiency. Throughout a six month period, no significant differences were found between the intervention and control group.

During the same period in Norway, 34,741 adults received 5 ml of cod liver oil or a placebo with the same amount of corn oil. The study did not find an association between cod liver oil and respiratory infections. 

External factorsVaccination is still highlighted as the most efficient protection toward COVID-19.
The authors acknowledge that several factors may have impacted the results. In the UK, the participants were aware of the supplement they were taking, and there was no way to ensure that the control group participants did not take supplements outside the research environment.

In Norway, the participants were “fairly young,” and most were healthy with adequate vitamin D levels at the start of the study.

Vaccination was being rolled out throughout both trials, which may play a significant role.

However, the authors note that the trials have strengths, such as using RT-PCR swab tests to confirm infections among the participants. Additionally, the two trials align with prior research stressing that there is no link between COVID-19 risk and vitamin D supplements. 

“Vaccination is still the most effective way to protect people from covid-19, and vitamin D and cod liver oil supplementation should not be offered to healthy people with normal vitamin D levels,” says Peter Bergman, professor at Karolinska Institutet, Sweden. 

Bergman adds that clinicians should focus on people in risk groups with vitamin D deficiency, such as the elderly with chronic diseases, pregnant women and people with low sun exposure. 

Vitamin D in previous headlines
The Council of Responsible Nutrition (CRN) previously highlighted a “significant link” found in 13 meta-analyses from more than 100 clinical trials on COVID-19 and vitamin D. 

“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,” Luke Huber, vice president of scientific and regulatory affairs at CRN, previously 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.” 

In the UK, over 2.5 million people at risk for severe COVID-19 infections received free vitamin D supplements. However, the government highlighted the need for significant results on the linkage and emphasized the lack of sufficient evidence.

Due to the pandemic, the CRN previously highlighted that vitamin D supplementation in the US increased to the highest levels in 20 years.

Edited by Beatrice Wihlander