Cod liver oil reduces painkiller use

“Two teaspoons of cod liver oil a day can cut the number of powerful painkillers needed to ease the pain of arthritis”, reports the Daily Mail . Patients who were given the supplements “were able to reduce their daily dose of anti-inflammatory drugs”, the newspaper says. These findings are important because the long-term use of anti-inflammatory drugs “can double the threat of heart attack and raise the risk of strokes and heart disease”, the Mail adds.

The reports are based on a small study in people with rheumatoid arthritis that showed the potential benefits of cod liver oil capsules in reducing the use of non-steroidal anti-inflammatory drugs (NSAIDs). The picture is complicated because the people taking the capsules were also on other drugs for their rheumatoid arthritis, and the study did not aim to reduce the dosages of these other medications. Not all people with rheumatoid arthritis will be able to reduce their NSAID dosage with cod liver oil capsules, and some people will not be able to stick with the daily regimen of 10 capsules. Although cod liver oil supplements may be worth considering by some people with rheumatoid arthritis, patients should talk to their doctor before making any drastic changes in the medicines they take.

Where did the story come from?

Dr Bernat Galarraga and colleagues from the Ninewells Hospital and Medical School in Dundee; the Western General Hospital in Edinburgh, and the University of Dundee, carried out this research. The study was funded by Willem Van Dias and Seven Seas Ltd, who sell cod liver oil capsules and other food "supplements". It was published in the peer-reviewed medical journal: Rheumatology .

What kind of scientific study was this?

This was a double-blind randomised controlled trial looking at whether taking high strength cod liver oil capsules could reduce the need for specific painkillers (NSAIDs) in people with rheumatoid arthritis. Cod liver oil contains the essential fatty acids DHA and EPA, which are thought to have anti-inflammatory effects.

The researchers enrolled 97 people aged 37 to 78 years old with rheumatoid arthritis (who had had the disease for an average of 13 years) from the rheumatology departments of two hospitals in Dundee and Edinburgh. To be included in the study, the person’s disease and medication had to have been stable for the past three months, and they had to have been taking regular NSAID medication. People with unstable disease that required changes in medication, those taking high doses of steroids, those with other severe diseases or those already taking supplements containing essential fatty acids were excluded.

Eligible participants were assigned at random to nine months treatment of either daily capsules containing a mixture of cod liver oil and fish oil (Seven Seas Marine Oil 1 capsules), containing 10g of oil in total, or identical air filled capsules (a placebo). At three and nine months, blood samples were taken to measure the levels of the essential fatty acid EPA (contained in cod liver oil) to see if participants had been taking their capsules.

Participants were also asked to record their daily NSAID use. After 12 weeks, participants were asked to gradually reduce their use of NSAIDs, and then stop using them if possible. The researchers calculated how much NSAID medication participants were using on average daily, how severely they were affected by their disease, and how active their disease was at the start of the study, as well as at four, 12, 24 and 36 weeks. The researchers then looked at how these levels changed over the study in the cod liver oil and placebo groups. They were primarily interested in comparing what proportion of people in each group had been able to reduce their daily NSAID use by more than 30% over the course of the study. Any participants who dropped out of the study were included in analyses, and assumed to have not reduced their NSAID usage by more than 30%.

What were the results of the study?

Only 60% of participants completed the full nine-month study period. More people in the cod liver oil group (39%) were able to reduce their NSAID intake by more than 30% compared with the placebo group (10%). This reduction was still significant following exclusion of the seven people (four in the cod liver oil group and three in the placebo group) whose use of other medications (such as steroids) increased during the study.

In general, there was no difference between the groups in the severity or activity of the disease on any of the measures used, except for a small but significant reduction in self-reported pain in the cod liver oil group compared with the placebo group. There was no difference between the groups in the type or number of side effects experienced, which were mostly mild.

What interpretations did the researchers draw from these results?

Researchers concluded that cod liver oil capsules could be used by people with rheumatoid arthritis to cut their NSAID intake.

What does the NHS Knowledge Service make of this study?

This well-designed study provides some evidence that people with stable rheumatoid arthritis may be able to reduce their intake of NSAIDs by taking cod liver oil supplements. There are some points to note about the study:

  • All participants in this study were taking NSAIDs, but it is not possible to say how much they were taking as the average doses at the start of the study were not given, and the results are given as percentage reductions in dose only. Also, there is not much information provided on the type of NSAID that were being used. There are a large number of NSAID drugs, and anti-inflammatory properties vary considerably from those in over-the-counter NSAIDs such as ibuprofen, to more potent medications such as indometacin.  
  • Although this was a double-blind study, participants may have been able to guess what they were taking because of the fishy aftertaste of the cod liver oil capsules, and the difference between air-filled and oil-filled capsules. This knowledge may have affected people’s willingness to reduce their NSAID dosage. 
  • The authors of the study note that the high level of withdrawals is a limitation to their study, and suggest that this was in part linked to people’s unwillingness to take 10 extra capsules a day and to digestive system problems when taking capsules.
  • Most people on this study were also taking disease-modifying anti-rheumatic drugs (DMARDS) for their rheumatoid arthritis, which, rather than providing pain and inflammation relief as NSAIDs do, are drugs used to actually “treat” the condition. They have an effect upon the body’s immune response, and can suppress the disease process and alter its progression. The study did not attempt to see whether cod liver oil use affected the use of these drugs. 
  • All people in this study had stable rheumatoid arthritis. These results may not be applicable to those with severe disease, and cannot be generalised to those with other arthritic conditions.

People with rheumatoid arthritis should consult their doctor before making any drastic changes in their medication.

Sir Muir Gray adds...

If I had rheumatoid arthritis, I would give the oil a go.

NHS Attribution