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 Sep 7;378:e071245. doi: 10.1136/bmj-2022-071245.

Abstract

Objective: To determine if daily supplementation with cod liver oil, a low dose vitamin D supplement, in winter, prevents SARS-CoV-2 infection, serious covid-19, or other acute respiratory infections in adults in Norway.

Design: Quadruple blinded, randomised placebo controlled trial.

Setting: Norway, 10 November 2020 to 2 June 2021.

Participants: 34 601 adults (aged 18-75 years), not taking daily vitamin D supplements.

Intervention: 5 mL/day of cod liver oil (10 µg of vitamin D, n=17 278) or placebo (n=17 323) for up to six months.

Main outcome measures: Four co-primary endpoints were predefined: the first was a positive SARS-CoV-2 test result determined by reverse transcriptase-quantitative polymerase chain reaction and the second was serious covid-19, defined as self-reported dyspnoea, admission to hospital, or death. Other acute respiratory infections were indicated by the third and fourth co-primary endpoints: a negative SARS-CoV-2 test result and self-reported symptoms. Side effects related to the supplementation were self-reported. The fallback method was used to handle multiple comparisons.

Results: Supplementation with cod liver oil was not associated with a reduced risk of any of the co-primary endpoints. Participants took the supplement (cod liver oil or placebo) for a median of 164 days, and 227 (1.31%) participants in the cod liver oil group and 228 (1.32%) participants in the placebo group had a positive SARS-CoV-2 test result (relative risk 1.00, multiple comparison adjusted confidence interval 0.82 to 1.22). Serious covid-19 was identified in 121 (0.70%) participants in the cod liver oil group and in 101 (0.58%) participants in the placebo group (1.20, 0.87 to 1.65). 8546 (49.46%) and 8565 (49.44%) participants in the cod liver oil and placebo groups, respectively, had ≥1 negative SARS-CoV-2 test results (1.00, 0.97 to 1.04). 3964 (22.94%) and 3834 (22.13%) participants in the cod liver oil and placebo groups, respectively, reported ≥1 acute respiratory infections (1.04, 0.97 to 1.11). Only low grade side effects were reported in the cod liver oil and placebo groups.

Conclusion: 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.

Trial registration: ClinicalTrials.gov NCT04609423.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • COVID-19* / prevention & control
  • Cod Liver Oil* / therapeutic use
  • Dietary Supplements*
  • Humans
  • SARS-CoV-2
  • Vitamin D* / therapeutic use

Substances

  • Vitamin D
  • Cod Liver Oil

Associated data

  • ClinicalTrials.gov/NCT04609423