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Omega-3s may provide no cardiovascular health benefit
Certain omega-3 fatty acids — such as those found in oily fish and walnuts — had little or no effect on cardiovascular health or mortality, according to data recently published in Cochrane Database of Systematic Reviews.
“Guidelines recommend increasing omega-3-rich foods, and sometimes supplementation, but recent trials have not confirmed this,” Asmaa S. Abdelhamid, MD, MSc, MBBCh, of Norwich Medical School and University of East Anglia in England and colleagues wrote.
Abdelhamid and colleagues reviewed 72 randomized clinical trials involving 112,059 participants at varying cardiovascular risk. Some participants consumed omega-3 fatty acid-rich or enriched foods, but most participants’ intake was from capsules. The trials studied ranged from 1 to 6 years in length, most were of moderate GRADE quality, and were performed in mostly high-income countries, according to researchers.
Findings suggested that increasing low-chain omega-3 fatty acid intake had little or no effect on:
- coronary heart disease mortality (RR = 0.93; 95% CI, 0.79-1.09);
- cardiovascular mortality (RR = 0.95; 95% CI, 0.87-1.03);
- arrhythmia (RR = 0.97; 95% CI, 0.9-1.05);
- all-cause mortality (RR = 0.98; 95% CI, 0.9-1.03);
- cardiovascular events (RR = 0.99; 95% CI, 0.94-1.04); and
- stroke (RR = 1.06; 95% CI, 0.96-1.16).
In addition, increasing alpha-lincolenic acid (ALA) intake probably made little or no difference in cardiovascular mortality (RR = 0.96; 95% CI, 0.74-1.25), coronary heart disease events (RR = 1; 95% CI, 0.8-1.22), and all-cause mortality (RR = 1.01; 95% CI, 0.84-1.2). ALA slightly reduced the risk for cardiovascular events (from 4.8% to 4.7%); and probably reduced risk for arrhythmia (3.3% to 2.6%) and coronary heart disease mortality (from 1.1% to 1%). The effects on stroke were unclear, according to researchers.
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“Eating more ALA (for example, by increasing walnuts or enriched margarine) probably makes little or no difference to all-cause or cardiovascular deaths or coronary events but probably slightly reduce cardiovascular events, coronary mortality and heart irregularities,” researchers wrote. “There is [also] little evidence of effects of eating fish.”
Researchers wrote that based on their findings, official recommendations supporting supplemental long chain omega-3 fatty acid intake should be reviewed and no further trials should be initiated until the results ongoing trials have reported. Only then should trials commence that examine ALA and dietary patterns in lower and higher income countries that assess baseline intake and use biomarkers to assess compliance and cardiovascular benefits.
Abdelhamid and colleagues also noted that previously reported benefits from omega-3 fatty acids may have been spurred from trials with higher risk for bias. – by Janel Miller
Disclosures: The authors report no relevant financial disclosures.
Perspective
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Before you decide whether omega-3s are beneficial to human health or not, it’s important to understand some of the shortcomings of the research that make it challenging to draw definitive conclusions, or even compare studies with one another.
For example, most studies rely on dietary recall, which is notoriously inaccurate. It’s only natural for participants, who generally recognize fish as a healthy choice, to overestimate their fish consumption. Even if participants do accurately recall how much fish they ate over a certain amount of time, say 6 oz a week, it is almost impossible to estimate the true quantity of omega-3s they obtained. Was the salmon they ate grown in a fish farm with a corn diet (high in omega-6, low in omega-3), or was it wild Pacific salmon? Did they eat 6 oz of tuna in a can with water or in oil, which can absorb some of the nutrients?
Additionally, in studies where researchers gave omega-3 supplements, it is often unknown if participants received long-chain fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which we know reduce inflammation, or alpha-linolenic, a shorter chain fatty acid form, which has different effects. Were the supplements taken with food or on an empty stomach, where they won’t be absorbed? If we assume all study recipients received exactly 1,000 mg of EPA and DHA throughout the study, can we also confirm that researchers obtained participants’ baseline omega-3 levels? If an individual already had high omega-3s, it might be expected to not see much of an effect. On the other hand, those who started with low omega-3s and received a supplement, may show beneficial effects.
However, if you average him/her with the person with baseline-high omega-3s, they tend to cancel one another and authors of a published study may conclude that it’s a “negative” study, meaning omega-3s don’t have a benefit for what they were studying.