Chance News 85

Fish oil

Weighing the evidence on fish oils for heart health
by Anahad O’Connor, Well blog, New York Times, 11 April 2012

According to O'Connor,

Fish oil supplements have become some of the most popular dietary pills on the market, largely on the strength of medical research linking diets high in baked and broiled fish to lower rates of heart disease. Across the United States, annual sales of purified fish oil, commonly sold as omega-3 fatty acids, are in the neighborhood of a billion dollars. And in some parts of Europe, doctors routinely prescribe fish oils to patients with heart disease.

People who put their faith in fish oil supplements may want to reconsider. A new analysis of the evidence casts doubt on the widely touted notion that the pills can prevent heart attacks in people at risk for cardiovascular disease.

And well the people might. O’Connor is referring to “Efficacy of Omega-3 Fatty Acid Supplements (Eicosapentaenoic Acid and Docosahexaenoic Acid) in the Secondary Prevention of Cardiovascular Disease; A Meta-analysis of Randomized, Double-blind, Placebo-Controlled Trials” by S.M. Kwak, et al., to appear in the Archives of Internal Medicine. Not only did:

Our meta-analysis showed insufficient evidence of a secondary preventive effect of omega-3 fatty acid supplements against overall cardiovascular events among patients with a history of cardiovascular disease,

But also:

Furthermore, no significant preventive effect was observed in subgroup analyses by the following: country location, inland or coastal geographic area, history of CVD, concomitant medication use, type of placebo material in the trial, methodological quality of the trial, duration of treatment, dosage of eicosapentaenoic acid [EPA] or docosahexaenoic acid [DHA], or use of fish oil supplementation only as treatment.

Discussion

1. The authors started their meta-analysis with 1007 articles; eventually, after 181 studies were excluded as duplicates and others were dropped out for various other reasons, they were left with “14 randomized, double blind, placebo-controlled trials.” The total number of subjects in the 14 trials was 20, 485. As stated above, statistical significance was not to be seen. Two large studies of 11,234 and 18, 645 subjects, respectively which did show beneficial effects from fish oil were not included in the 14; they were rejected because they were “open-label” studies. Why are open-label studies suspect?

2. Why did the subjects in the placebo arm of the 14 studies receive various vegetable oils? Some of those subjects in the placebo arm received olive oil. Why might this “have disguised the ‘true’ benefit of omega-3 fatty acid supplementation?”

3. If not fish oil, O’Connor says the authors conclude that

it may make the most sense to spend your money on actual fish, rather than fish oil supplements.

They argue that by eating fish, you end up replacing other less healthy protein sources, like processed foods and red meat. For that reason, a diet high in fatty fish — one that includes at least two servings a week — may make a difference over the long term, they say.

If the above is correct, why are so many people eschewing fish for fish oil?

Submitted by Paul Alper