Many of us are eating fish or taking fish oil supplements, hoping that they will prevent heart attacks and the associated premature death. As it turns out, they may do neither.
I’ve been sitting on this research report a few years, waiting until I had time to dig into it. That time never came. The full report is free online (thanks, British Medical Journal!). I scanned the full paper to learn that nearly all the studies in this meta-analysis used fish oil supplements, not the cold-water fatty fish the I recommend my patients eat twice a week.
Here’s the abstract:
Objective: To review systematically the evidence for an effect of long chain and shorter chain omega 3 fatty acids on total mortality, cardiovascular events, and cancer.
Data sources: Electronic databases searched to February 2002; authors contacted and bibliographies of randomised controlled trials (RCTs) checked to locate studies.
Review methods Review of RCTs of omega 3 intake for 3 6 months in adults (with or without risk factors for cardiovascular disease) with data on a relevant outcome. Cohort studies that estimated omega 3 intake and related this to clinical outcome during at least 6 months were also included. Application of inclusion criteria, data extraction, and quality assessments were performed independently in duplicate.
Results: Of 15 159 titles and abstracts assessed, 48 RCTs (36 913 participants) and 41 cohort studies were analysed. The trial results were inconsistent. The pooled estimate showed no strong evidence of reduced risk of total mortality (relative risk 0.87, 95% confidence interval 0.73 to 1.03) or combined cardiovascular events (0.95, 0.82 to 1.12) in participants taking additional omega 3 fats. The few studies at low risk of bias were more consistent, but they showed no effect of omega 3 on total mortality (0.98, 0.70 to 1.36) or cardiovascular events (1.09, 0.87 to 1.37). When data from the subgroup of studies of long chain omega 3 fats were analysed separately, total mortality (0.86, 0.70 to 1.04; 138 events) and cardiovascular events (0.93, 0.79 to 1.11) were not clearly reduced. Neither RCTs nor cohort studies suggested increased risk of cancer with a higher intake of omega 3 (trials: 1.07, 0.88 to 1.30; cohort studies: 1.02, 0.87 to 1.19), but clinically important harm could not be excluded.
Conclusion: Long chain and shorter chain omega 3 fats do not have a clear effect on total mortality, combined cardiovascular events, or cancer.
If you’re taking fish oil supplements on your doctor’s advice, don’t stop without consulting her. The study at hand doesn’t address whether eating cold-water fatty fish twice a week prevents heart attacks and premature death.
Steve Parker, M.D.
Reference: Hooper, Lee et al. Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review. BMJ 2006;332:752-760 (1 April), doi:10.1136/bmj.38755.366331.2F (published 24 March 2006).
I don’t see how these results negate the basic biochemistry. Cell membrane phospholipids fill up with
various highly-unsaturated fatty acids based on dietary intake, and these
fatty acids are chosen at random to be transformed into the eicosanoids, the local signalling
molecules that respond to inflammation, etc. Taking random people who are swimming in linoleic acid. giving them random amounts of Omega-3 and then averaging the results does not seem to me to be a sensible way to explore the medical ramifications.
Hey, Jim. You’re suggesting that the effects of omega-3 supplementation may depend on whether the baseline diet contains lots of omega-6 fatty acids or not. You may be right.
I have a problem with supplements like fish oil that are liquid. In the ingredients, they list soy oil as part of the pill. Soy oil and all soy products are endocrine disruptors and should be avoided in my opinion. What do you think?
Cathy, I never new fish oil capsules had soy oil. If so, I’m guessing there’s not enough in 1-2 capsules/day to make any difference.
I agree with Jim Jozwiak, it is the ratio that is important–read the papers by W.E. Lands. There are many powerful forces that don’t want this to be true and will do whatever they can to confuse the issue.
Also studies of a few months or even a couple years looking at death as an endpoint seem designed to fail to find an effect.
Yes, Dr. Lores, I agree it will take longer to see an effect on mortality or morbidity unless N is huge.
I do think that if you seriously work at changing the ratio of omega-6/3 it can have dramatic effects in a month or 2. It did for me–fixed blood pressure, heart rhythm, and arthritis pain in 3 weeks–after 1 yr on the diet my ratio was 55/45. Those kinds of physiological changes could reduce mortality in relatively short time, but my guess is that in most of these studies the omega-6/3 ratio was not changed more than a few percent.,
Thanks for sharing your experience, Dr. Lores.
The study is pretty old. I think we are much better now at trying to make sure our fish oil is not allowed to go rancid. I expect the rancidity of the oil may affect results.