Cod Liver Oil Supplementation Not Found to Impact COVID-19 Prevention

Use of cod liver oil supplements during the winter months does not reduce the occurrence of SARS-CoV-2 infection, COVID-19, or other acute respiratory infections compared with placebo, according to a study published in The BMJ. The study authors sought to clarify whether using cod liver oil, which is a low vitamin D supplement, in the winter would prevent any serious acute respiratory infections in adults.

The quadruple-blinded, randomized, placebo-controlled trial was conducted between November 10, 2020, and June 2, 2021. The investigators analyzed 34,601 adults between 18 and 75 years of age in Norway who did not take daily vitamin D supplements.

Among the study population, more than half were women (64.5%), with a mean age of 44.9 years, and mean body mass index of 26.1 at baseline. The majority of the study population (75.5%) did not use vitamin D supplements prior to enrollment, 61.5% consumed fatty fish, and 39.8% reported ≤30 hours of exposure to the sun from July to October 2020.

A subsample analyses for SARS-CoV-2 antibodies at baseline found that 28 of 1333 participants (2.1%) had a positive antibody test result. During the intervention, 6233 individuals in the cod liver oil group and 6097 individuals in placebo groups received ≥1 doses of a SARS-CoV-2 vaccine.

The participants completed baseline questionnaires before being randomized 1:1 to receive cod liver oil or placebo, which covered personal data, questions related to vitamin D, and other questions.

Each participant was administered 5 mL/day of cod liver oil or placebo for up to 6 months. The study had 4 primary endpoints:

• A positive SARS-CoV-2 test result determined by reverse transcriptase-quantitative polymerase chain reaction.
• Serious COVID-19 classified as self-reported dyspnea, admission to hospital, or death.
• Other acute respiratory infections (negative SARS-CoV-2 test result).
• Other acute respiratory infections (self-reported symptoms).

Both the cod liver oil and the placebo were flavored with lemon. Both products were blind tested by an experienced taste panel, and the participants were encouraged to take a 5 mL measurement spoon or tablespoon supplement at the same time each day, according to specific instructions they received with the product.

“Our trial had a practical and realistic approach to supplementation with vitamin D for the prevention of COVID-19 and other acute respiratory infections, testing whether those not taking vitamin D supplements at the start of the trial would benefit from supplementation during the winter,” the study authors wrote.

The results highlighted that supplementation with cod liver oil was not associated with a reduced risk of any of the co-primary endpoints.

In 121 participants, serious COVID-19 was identified in the cod liver oil group vs 101 participants in the placebo group. Further, 8546 and 8565 participants in the cod liver oil and placebo groups had ≥1 negative SARS-CoV-2 test results, respectively, and 3964 and 3834 participants in the cod liver oil and placebo groups reported ≥1 acute respiratory infections, respectively.

Only low-grade adverse effects were reported were in the cod liver oil and placebo groups.

“Daily supplementation with cod liver oil, a low dose vitamin D, eicosapentaenoic acid, and docosahexaenoic acid supplement, for six months during the SARS-CoV-2 pandemic among Norwegian adults, did not reduce the incidence of SARS-CoV-2 infection, serious COVID-19, or other acute respiratory infections,” the study authors concluded.

REFERENCE

Brunvoll S H, Nygaard A B, Ellingjord-Dale M, Holland P, Istre M S, Kalleberg K T et al. Prevention of covid-19 and other acute respiratory infections with cod liver oil supplementation, a low dose vitamin D supplement: quadruple blinded, randomised placebo controlled trial. BMJ 2022; 378 :e071245 doi:10.1136/bmj-2022-071245.