Fish oils or Omega-3 (n -3) polyunsaturated fats are found in seafood, such as salmon, trout, herring, tuna, and mackerel, and in walnuts, soy, canola oils, and flaxseed oils. Some nutrition experts advocate for increased consumption of omega-3 polyunsaturated
fats for their benefits including lowering triglyceride levels, reducing the risk of potentially fatal abnormal heart rhythms, and
because they may make platelets less likely to form the blood clots that can cause a heart attack or stroke. Increased consumption of omega-3 fatty acids from fish, fish oil supplements, or plant sources has been considered to be a dietary strategy to
prevent coronary heart disease.
However, randomized placebo-controlled studies have had mixed results, and fish seems to be more likely to improve cardiovascular
health than the consumption of fish oil supplements. According to a 2013 review, with the advent of the wide use of statins and other medical therapies for CVD prevention, the use of fish oil supplements or even eating fish to prevent CVDs is less likely to be an efficacious strategy. A carefully carried out 2018 meta-analysis has found that fish oil supplements provide no benefit with regard to cardiovascular disease or all-cause mortality. This finding confirms the similar conclusion of the U.S. Agency for Healthcare Research and Quality.
A 2018 Cochrane systematic review that considered the results of 25 trustworthy randomized trials came to the same conclusion, i.e., that increasing consumption of the omega-3s Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), has little or no effect on all-cause mortality or cardiovascular health (coronary heart deaths, coronary heart disease events, stroke or heart irregularities). The review observed that long-chain omega-3 fats probably did reduce triglycerides and HDL cholesterol.
In 2019, after five years of study, VITAL, a well-designed clinical trial of supplementation with a high dose (1 g per day) of n–3 fatty acids, did not find a lower incidence of major cardiovascular events or cancer than a placebo. However, an analysis that excluded the first two years of follow-up found an 11% lower risk (hazard ratio of 0.89) for major cardiovascular events in the n–3 group as compared to the placebo group. Although secondary endpoint conclusions are less reliable, the data also suggested that compared to the placebo group, Blacks and those with low fish intake in the n-3 group had a significantly lower risk of myocardial infarction. Additional analyses from the VITAL study are planned, and confirmation of the secondary findings by future trials is needed.
A 2019 meta-analysis that included the findings from VITAL found that daily marine omega-3 supplementation is moderately effective. After an average of five years of use, omega-3 supplementation provided a modest 3% to 8% reduction in CVD endpoints. The study found lower rates of myocardial infarction, coronary heart disease death, total coronary heart disease, cardiovascular disease death, and total cardiovascular disease, but no benefits were found for stroke. Risk reductions were linearly proportional to the dose of marine omega-3 supplementation, suggesting that greater cardiovascular benefits may be achieved at higher doses of marine omega- 3 supplementation. The study authors concluded that “Despite the modest effect sizes for some of the CVD outcomes, the use of marine omega-3 supplementation may still help prevent large absolute numbers of CVD events, given the high incidence rates of CVD worldwide.”
A reasonable conclusion is that additional research on high doses of marine omega-3 supplementation is needed. So far, the research suggests that there are health benefits from eating fish, and, perhaps small benefits from consuming high dose fish
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