Monday’s Medical Myth: Fish Oil Is Good For Heart Health
Did you hold your nose and take your daily dose of fish oil this morning? Or perhaps you opted for an odour-free capsule? Well, you’re not alone. Around one in four Australians take fish oil supplements to improve their health. After all, it’s supposed to be good for the heart. Right?
The Heart Foundation even has a Fish Oil Program aimed at increasing awareness of the benefits of marine-derived omega 3 fatty acids on heart health. Its 2008 Position Statement on Fish Oil recommended adults consume at least 500mg of omega-3 a day to lower the risk of heart disease.
If you’re interested in learning more about the complexities of fatty acid metabolism, you can find readable technical summaries in the opening part of this paper or a more comprehensive version on Wikipedia. But in short, researchers are interested in the potential benefits of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA).
The fish oil story reflects the challenges involved in translating research evidence into community knowledge and behaviour. And it shows why those who stand by evidence in medicine must be prepared to give up their most cherished beliefs if the science demands it.
The Heart Foundation 2008 Position Statement is a good place to start. It is a serious public health document which takes a balanced, evidence-based approach.
A table in the document sets out the levels of evidence supporting the rationale for its recommendations. But only one finding has level one (the highest level) evidence to support it – that is, the statement that fish oil supplements have a favourable effect on serum triglyceride levels and HDL (good) cholesterol levels.
Although one might assume this to be a good thing, there is not a similar level of support for the direct link between fish oil and improved heart health. It may be that this positive effect on blood lipid ratios is too small to have a useful benefit when applied routinely to real, paying customers outside of clinical trials.
Most of the other planks of the position have level two or three evidence, which translates to positive results in individual studies without support from meta-analysis or systematic reviews of multiple studies. The number of studies with negative or inconclusive results does not affect these ratings.
The Heart Foundation noted this shortfall and designated areas for further study which include doing higher-level reviews and better studies with robust methodology. As an organisation which strives to use the best evidence to form policy, I expect it will update and amend its recommendations to reflect the findings of such new studies as they come in.
The biggest gap in the research on fish oil supplements has been between their effects in test tubes and small pilot studies, and the real world of clinical practice. A definite mechanism for how omega 3 fatty acids provide cardiac protection has never been agreed on, which makes predicting clinical effects in real patients difficult.
An early systematic review in 2006 supported fish oil for heart health. But reading the body of the paper, it’s hard to see how the researchers came to such a positive conclusion. They comment throughout on the variable methods of studies reviewed and the mixed outcomes reported. They mostly favour a small positive effect but don’t consistently point the same way.
There are also other, similar reviews from the early 2000s which draw mixed conclusions.
In the last few months there have been major systematic reviews in the Archives of Internal Medicine, the Annals of Internal Medicine and the Journal of the American Medical Association (JAMA) which have all separately failed to support a clear effect on people in the real world.
The JAMA study demonstrates pretty comprehensively that omega 3 supplements aren’t effective at preventing cardiac problems such as heart attacks, stroke, sudden death and arrhythmias. What makes this study more credible is that it has included both dietary and supplement studies. Whether you are getting your omega 3s from a capsule or from tins of tuna, it seems unlikely that they are doing much good.
So what does this all mean for those taking omega 3 supplements?
Well, fish oil may be reasonable as an add-on therapy for very high-risk cardiac patients who can’t tolerate other, more effective treatments.
Research on fatty acid supplementation is likely to continue and some specific use may still be found for such supplements. The evidence that omega 3 can reduce the symptoms of inflammatory arthritis, for example, still appears promising.
Efforts to encourage Australians to eat more fish should push on, because preferring fish to red meat is still a worthwhile change for other health reasons.
But it’s becoming increasingly clear that having a quarter of the population on fish oil as a preventive supplement is an unjustifiable expense. I will await the self-regulatory response from advertisers of fish oil products to this avalanche of new evidence with interest, as should the Therapeutic Goods Administration.