Mayo Clinic evidence review challenges negative reports, links higher levels to reduced risks 01/16/2017
Recently, we’ve seen a string of negative stories about fish oil and heart disease.
Sadly, in almost every case, the study authors or media reports have been misleading.
For example, see Public TV Airs a Fishy Omega-3 Story, and its links to related reports.
Let’s take a look at two recent evidence reviews, both of reaffirm the idea that omega-3s help prevent heart disease and heart-related deaths.
Large global study links higher omega-3 levels to lower heart risk
Dozens of researchers collaborated on a meta-analysis of 19 “prospective cohort” studies, whose results were published last August (Del Gobbo LC et al. 2016).
Prospective cohort studies follow people over time, looking for links between intakes or blood levels of omega-3 fats and the risk for developing a disease.
The study was led by award-winning epidemiologist Liana C. Del Gobbo, Ph.D., from the Stanford University School of Medicine.
The 19 studies analyzed by her team included 45,637 people – roughly equal numbers of men and women — in 16 countries.
In each case, the original studies compared the participants’ omega-3 blood and tissue levels to their risk for death related to coronary heart disease (CHD).
Dr. Del Gobbo’s group calculated that higher blood and tissue levels of each type of omega-3 fat reduced the risk of death from CHD by about 10%.
And that risk reduction applied regardless of whether the omega-3s came from plant foods (ALA) or seafood (DHA and EPA).
As the authors wrote, “… [higher blood and tissue levels] of seafood and plant-derived omega-3 fatty acids are associated with a lower incidence of fatal CHD.”
Del Gobbo told Medscape that her team’s findings fit with lab evidence showing that "a major effect of these seafood-based omega-3 fatty acids is to stabilize heart membranes and reduce the risk of ventricular fibrillation [risky heart rhythms] ...”.
She went on to note that “people were consuming these omega-3s primarily from food”, not from fish oil supplements.
Del Gobbo said that doctors should advise patients to eat “at least two to three servings of fatty fish a week, which is consistent with recommendations from the American Heart Association”, as part of a Mediterranean-style diet rich in fruits, vegetables, nuts, and olive oil.
Mayo Clinic meta-analysis supports fish oil for heart health
The latest evidence review, published last week, comes from researchers at the Mayo Clinic.
The authors reviewed 18 randomized controlled clinical trials and 16 prospective cohort studies, which involved about 93,000 and 732,000 subjects, respectively (Alexander DD et al. 2017).
The Mayo Clinic team examined outcomes such as heart attacks (myocardial infarction or MI), sudden cardiac death – half of all heart-related deaths — and other heart-related fatalities.
Affirming the results of most prior studies, the Mayo Clinic researchers concluded that seafood-source omega-3s (EPA and DHA) reduce the risk of coronary heart disease (CHD).
These were the authors’ positive conclusions concerning the 18 clinical trials, in which participants were given either fish oil or placebo capsules:
- 16% average drop in risk among people with high triglyceride levels (over 150 mg/dL)
- 14% average drop in risk among people with high LDL cholesterol levels (over 130 mg/dL)
- 6% average drop in risk among all participants, which was deemed statistically non-significant.
The prospective cohort studies — which generally lasted longer than the clinical trials — compared the heart-health outcomes for people with high versus low intakes of seafood-source omega-3s (EPA and DHA).
The Mayo Clinic team concluded that the 16 prospective cohort studies showed an 18 percent average drop in CHD risk among participants with higher intakes of omega-3s.
The authors believe this finding from the prospective cohort studies supports the credibility of the statistically non-significant 6 percent drop seen among all participants in the clinical trials.
To quote Dr. Dominik Alexander, the study’s lead author, “The 6 percent reduced risk among [all participants in the] RCTs, coupled with an 18 percent risk reduction in prospective cohort studies — which tend to include more real-life dietary scenarios over longer periods — tell a compelling story about the importance of EPA and DHA omega-3s for cardiovascular health.”
We should note that study was supported by a grant from the leading fish oil trade association, called the Global Organization for EPA and DHA (GOED), which played no role in the design or analysis of the study, in the writing of the report, or in the decision to submit the article for publication.
Cardiologists see affirmation of omega-3s for heart health
An editorial accompanying the Mayo Clinic study — titled “The tide turns for a fish story” — highlighted its meaning and importance.
As the three cardiologists behind the editorial wrote, “... omega-3 fatty acid intake of at least 1 gram of EPA+DHA per day, either from seafood or supplementation (as recommended by the American Heart Association), continues to be a reasonable strategy.” (O'Keefe JH et al. 2016)
Among other things, the authors of the editorial recommended these steps for future studies:
- Recruit more people to account for dropout rates in longer trials.
- Detail how subjects are diagnosed, in order to create uniform diagnostic criteria.
- Measure baseline omega-3 intake or status of the participants to determine the extent to which it affects study results.
(Two of the three authors of the editorial have financial links to companies that produce omega-3 products.)
Want to learn more?
- Alexander DD, Miller PE, Van Elswyk ME, Kuratko CN, Bylsma LC. A Meta-Analysis of Randomized Controlled Trials and Prospective Cohort Studies of Eicosapentaenoic and Docosahexaenoic Long-Chain Omega-3 Fatty Acids and Coronary Heart Disease Risk. Mayo Clin Proc. 2017 Jan;92(1):15-29. doi: 10.1016/j.mayocp.2016.10.018.
- Del Gobbo LC et al. ω-3 Polyunsaturated Fatty Acid Biomarkers and Coronary Heart Disease: Pooling Project of 19 Cohort Studies. JAMA Intern Med. 2016 Aug 1;176(8):1155-66. doi: 10.1001/jamainternmed.2016.2925.
- Mozaffarian D, Lemaitre RN, King IB, Song X, Huang H, Sacks FM, Rimm EB, Wang M, Siscovick DS. Plasma phospholipid long-chain ω-3 fatty acids and total and cause-specific mortality in older adults: a cohort study. Ann Intern Med. 2013 Apr 2;158(7):515-25. doi: 10.7326/0003-4819-158-7-201304020-00003.
- O'Keefe JH, Jacob D, Lavie CJ. Omega-3 fatty acid therapy: The tide turns for a fish story. Mayo Clin Proc 2017;92:1-3. Editorial