It would have been nice if it were true that taking cod liver oil protected against Covid-19 - but alas a large Norwegian study finds that it makes no difference at all.

New Norwegian study: Cod liver oil does not protect against Covid-19

Taking cod liver oil with vitamin D does not protect against getting infected with the coronavirus, becoming seriously ill with Covid, or other respiratory infections.

“We are sure that the conclusion is correct, and it is a disappointing conclusion,” says researcher and doctor Arne Søraas to NTB, the Norwegian news agency.

“It would have been better for everybody if it were proven to be true that taking cod liver oil or vitamin D every day protected against Covid-19. But alas it does not,” he says.

Søraas has been in charge of the so-called Cod liver oil study, where almost 35,000 participants were monitored throughout the pandemic in order to find out whether taking cod liver oil – which contains a lot of vitamin D – could have a preventive effect on Covid-19. The results of the study were published yesterday in the British Medical Journal (BMJ).

Made no difference

In the period between 19 November 2020 and 13 April 2021, the participants – who were all above the age of 18 – were sent either cod liver oil or corn oil. Both oils were lemon flavoured. Participants were to take the oil every day throughout winter.

The researchers then examined whether the group that received cod liver oil to a lesser extent were infected with the coronavirus, developed serious Covid-19 or other colds – as well as other possible health benefits.

“We found nothing. No difference between the groups that suggest a preventive effect,” Søraas says.

Just as many respiratory infections

The background for the Cod liver study was a large meta-analysis and findings from what is know as ‘the great corona study’(link in Norwegian) in Norway. This study was started just as the pandemic hit Norway and aimed to track the spread of the virus. It appeared in this study that people who had been taking vitamin D-supplements to a lesser extent were getting ill with Covid-19 compared to those who had not.

It became important to find out whether vitamin D was the real reason for this.

The results clearly show that levels of vitamin D decreased throughout winter in those who received the placebo corn oil, while it increased in those who were taking cod liver oil.

But the levels of respiratory infections were the same.

British study finds the same

The findings correspond with the results of a British study which included 6,200 adults, and was also published yesterday in BMJ.

In the period between May to October 2021 participants were given either the recommended daily dose of vitamin D (20 micrograms), four times the daily dose (80 micrograms) or nothing.

None of the doses of vitamin D had any preventive effect on respiratory infections or Covid-19 in the following six months.

A massive amount of data

Søraas is also in charge of the previously mentioned corona study at Oslo University Hospital. With more than 140,000 participants who have been followed since the pandemic started, this is one of the world’s largest studies of the corona pandemic. More than 200,000 Norwegians have participated in total. Most of them believed that vitamin D would lead to less Covid-19, but that there might also be other preventive things present in those who had high levels of the vitamin.

The researchers teamed up with the company Orkla to find out if vitamin D prevents infections in and of itself, or if high levels of vitamin D within people is a marker for healthy lifestyles.

Diet, sun, supplements, and age are some of the factors that affect the levels.

“35,000 Norwegians have taken cod liver oil or a placebo every morning for six months, so we have managed to get an answer,” Søraas says.

“Now that we have established that taking supplements didn’t help, we can ask the next question: what is it with those individuals who have high levels of vitamin D that protects them against respiratory infections and Covid?” he asks.

More findings

Perhaps you must have taken the vitamin for years to achieve the effect.

“But most likely personality and lifestyle has a lot to do with it,” the researcher says.

“If you are somebody who is conscious about taking care of your health, take precautions to protect yourself and follow the advice of the authorities, then you are better protected against infections – and you are most likely also conscious of taking enough vitamin D or cod liver oil,” Søraas says.

He also mentions a few other findings from the study:

“We saw that getting vaccinated is very efficient. It protects against corona, at least the Delta-variant which was dominant during the study period. We saw a considerable decrease in the number of infected people when vaccination started,” Søraas says.

They also found that those who took cod liver oil did not have any negative side effects compared to those who were just taking the vegetable oil.

Translated by: Ida Irene Bergstrøm


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