Effects are disease dependent: Studies show no benefits in MS and cardiovascular disease
Omega-3 fatty acids are found in many substances, such as fish, supplements and even an approved drug. Fish oil is one of the most frequently used supplements, and we eat fish in the hope that it will prevent chronic diseases. We believed that the effects of omega-3s are beneficial, since they have anti-inflammatory properties and reduce triglycerides (Brit J. Pharmcol. 2008:153:S200-215; Am J Clin Nutr. 2003:77;300-307). But does the research into clinical outcomes confirm this, or is it conjecture?
The answer is complicated, since the effects seem to be disease dependent. On the one hand, omega-3 FAs are beneficial for Alzheimer’s, age-related macular degeneration, dry-eye syndrome, depression, anxiety and rheumatoid arthritis. On the other, omega-3s have no effect in cardiovascular disease, multiple sclerosis or cancer prevention, and may even increase the risk of prostate cancer. Let’s look at the studies.
The prevailing thought has always been that omega-3s, especially from fish oil, reduce the risk of stroke and heart disease. Unfortunately, one recent study did not show a beneficial outcome for secondary (second event) prevention of cardiovascular disease with supplemental fish oil.
These results were surprising to many in the medical community and went counter to the treatment paradigm. In the Korean Meta-analysis Study Group (a group of 14 randomized clinical trials, the gold standard of studies), the results did not show a reduction in heart attacks, all-cause mortality, sudden cardiac death, transient ischemic attacks or strokes (Arch Intern Med. online April 9, 2012).
In a commentary by a respected researcher at Harvard Medical School, Dr. Frank Hu, these results should be taken in stride — trials for fish oils have shown mixed results in cardiovascular disease. There were also flaws in the Korean meta-analysis: Many of the studies may have been too small, too short in duration and the primary endpoints were not focused on cardiovascular disease.
It will be interesting to see the effects in the VITAL trial, an ongoing primary prevention trial in cardiovascular disease using fish oil plus vitamin D (Contemp Clin Trials. 2012;33(1):159-171).
Right now, the evidence is inconclusive to recommend fish oil for cardiovascular disease. However, fish has benefits that go beyond omega-3s. It is a good source of protein and of astaxanthin, a member of the carotenoid family of phytochemicals (Arch Intern Med. online April 9, 2012).
Effect on cancer
In the SU.FOL.OM3 study, patients who had cardiovascular disease were given fish oil and vitamin B (B6, folate and B12) to reduce the risk of cancer and cancer deaths. The results were disappointing. In fact, with women, the fish oil increased the risk of cancer, though the number of cases was extremely small. It did not matter whether the fish oil was given alone or in combination with B vitamins — the results fell short of expectations (Arch Intern Med. 2012 Apr 9;172(7):540-7).
In a shocker, the Prostate Cancer Prevention Trial, fish consumption actually increased the risk of aggressive prostate cancer by 2.5 times when high levels of DHA (docosahexaenoic acid), an omega-3 FA, were found in the blood. This trial was observational and involved 3,461 men (Am J Epidemiol. 2011 Jun 15;173(12):1429-39). Before jumping to conclusions, know that other studies have shown that omega-3s either had no effect or potentially beneficial effects with prostate cancer (Am J Clin Nutr 2010;92(5):1223-1233).
Regardless, I would not recommend omega-3s to reduce the risk of cancer risk — especially prostate cancer. Those with a family history of high-grade prostate cancer should consult their physician about the risk-benefit ratio of consuming omega-3s in the form of fish and fish oil. This does not have any impact on omega-3s from other sources, such as from nuts and seeds, since these are low in DHA.
Since omega-3s have supposed anti-inflammatory effects and autoimmune diseases are based on inflammation, it would make sense to assume that multiple sclerosis patients would benefit from fish oil. However, in an RCT, there were no differences in either objective or subjective measures including MRI findings, frequency of relapse, quality of life and fatigue between the groups that took fish oil and not (Arch Neurol. online April 16, 2012).
Researchers even added the standard-of-care medication, interferon beta-1a, to both groups after six months. The only effects seen were from the drug therapy. This was the first RCT in MS with fish oil supplementation, and the size of the trial was small with only 92 patients.
Fish oil supplementation must be undertaken with caution. Does this mean we should avoid fatty fish and fish oils? Not at all. Even in trials with negative results, there are others to counterbalance them.
Next week, I will write about the positive contributions of omega-3s to disease prevention and treatment.
Dr. Dunaief is a speaker, author and local lifestyle medicine physician focusing on the integration of medicine, nutrition, fitness and stress management. For further information, go to the website www.medicalcompassmd.com and/or consult your personal physician.