Vitamin D, cod liver oil supplements may not protect against COVID-19

The first clinical study took place in the United Kingdom and was conducted by a research team from the Queen Mary University of London. Researchers enrolled 6,200 people ages 16 and over who were not currently taking vitamin D supplements.

Following a blood analysis of their vitamin D levels, researchers administered either a low or high dose of vitamin D to the study participants. After a six-month follow-up, scientists found at least one acute respiratory tract infection of any cause occurred in 5.7{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} of the low-dose vitamin D supplement group and 5{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} in the higher-dose group.

Additionally, 3.6{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} of participants in the low-dose vitamin D group and 3{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} in the higher-dose group developed COVID-19, compared to 2.6{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} of participants not offered a vitamin D supplement.

The second study was conducted by a research team from Oslo University Hospital in Norway.

“We were trying to prove that vitamin D actually could prevent COVID-19 and other respiratory tract infections,” principal investigator Dr. Arne Søraas in the Department of Microbiology at Oslo University Hospital explained to Medical News Today.

“There has been a lot of research into vitamin D as a ‘booster’ for the immune system and even meta-analyses that have shown it to be effective in preventing such infections. There was, therefore, a hope that it could also prevent COVID-19 which is also an airway infection.”
— Dr. Arne Søraas

This study focused on the use of a cod liver oil supplement to prevent acute respiratory infections and COVID-19. Cod liver oil contains high amounts of vitamin D, vitamin A, and omega-3 fatty acids.

Dr. Søraas said he also led the Norwegian Corona Cohort study where scientists followed 200,000 Norwegians through the pandemic.

“There we observed that cod liver oil users were less likely to catch COVID-19,” he said. “Cod liver oil is a widely used supplement in Norway.”

Dr. Søraas and his team administered cod liver oil or a placebo to about 34,600 adults not currently taking vitamin D supplements. After taking the cod liver oil or placebo for a median of 164 days, 1.31{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} of cod liver oil takers had developed COVID-19, compared to 1.32{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} of placebo takers. The cod liver oil group also had a higher percentage of those developing serious COVID-19 — 0.70{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} compared to 0.58{cfdf3f5372635aeb15fd3e2aecc7cb5d7150695e02bd72e0a44f1581164ad809} in the placebo group.

Additionally, the research team did not observe a reduction in the incidence of acute respiratory tract infections in those taking cod liver oil compared to those taking the placebo.

Dr. Søraas said the findings surprised him and his research team. “We would not have set up such a large project if we did not truly believe that we would find that vitamin D could prevent COVID-19,” he added.

“We will now follow all the participants for at least two years and study self-reported health outcomes, as well as health outcomes from national Norwegian registries, to identify any longer-term health effects of our intervention,” Dr. Søraas continued.

“Cod liver oil did increase vitamin D and omega-3 levels in the study — unsurprising, of course — and the study is a great opportunity to study rare side effects, as well other possible effects. All the 35,000 cod liver oil participants are also a part of the Norwegian Corona Cohort where we have a lot of the focus on long-COVID,” he added.

MNT also spoke with Dr. Jimmy Johannes, a pulmonologist and critical care medicine specialist at MemorialCare Long Beach Medical Center in Long Beach, CA, about these two studies. He said he was not particularly surprised by the results of these studies.

“Prior studies evaluating vitamin D supplementation on the prevention of acute infections had mixed results. [I] think if there’s any effect, it would be small,” he said.

When asked about the next steps he would like to see for this research, Dr. Johannes said: “If you’re really looking for an effect, you might need a larger study that’s better controlled to find any effect.”

“Having said that, [if] we think there’s an effect [and] it would be small, [it] therefore [raises] the question, would this effect be clinically important? And should we spend the expense of doing this kind of clinical trial that would be very expensive to do a well-controlled, large clinical trial to find this kind of effect?” he concluded.