Overwhelming evidence links fish oil and fish-rich diets to reduced risks for death and heart-related crises like heart attack and stroke.
And the findings of a very large study — involving more than 400,000 middle-aged British men and women — reinforce the reality of those benefits.
American and Chinese researchers compared the British participants’ diets and fish oil use to their medical records.
Their analysis found these links between taking fish oil and health outcomes:
Some caveats about the study’s conclusions
Although this one involved a huge number of participants, epidemiological studies can't prove a cause-effect relationship between a drug or nutrient and health outcomes.
In addition, the researchers lacked information on the dose of omega-3s in each participant's fish oil supplement, and on how long they’d been taking fish oil.
Controlled clinical trials — if properly designed — are generally the most reliable way to test the health effects of a drug or nutrient.
But the authors of the new study made this cogent comment: “… the performance of fish oil supplements in randomized controlled trials [is] assessed under controlled circumstances … [so] complementary information on the effectiveness of fish oil is needed through evaluation in [the] real life settings of large scale cohort [epidemiological] studies [like this one].”
And, when it comes to clinical trials, quality matters. Many clinical trials testing fish oil’s effect on cardiovascular risks have been too small, too short, and/or used low doses of omega-3s.
Most clinical trials also fail to account for the adverse, omega-3-blunting cardiovascular effects of the extremely high intakes of omega-6-fats (mostly from vegetable oils) in the standard American/Western diet.
Good news about fish oil follows two recent clinical-evidence reviews
This encouraging news — which echoes those of many prior population and clinical studies — follows the less positive findings of a recent clinical-evidence review, whose authors calculated a smaller cardiovascular benefit from regular fish oil.
However, a clinical-evidence review published last year reached more positive conclusions: see Omega-3 Heart Benefits Affirmed by Big New Review.
How the new study was conducted
A team of researchers based in China and the US drew on data from the UK Biobank — a large study involving more than 500,000 British men and women who underwent physical measurements, provided detailed diet/lifestyle information, allowed access to their medical records, and gave blood, urine and saliva samples.
The authors of the new study analyzed the data from 427,678 men and women between 40 and 69 years old, free of heart disease or cancer, who were enrolled in the UK Biobank study from 2006 to 2010 and completed a survey on their use of supplements, including fish oil.
Death certificates and hospital records were used to monitor deaths from any cause, heart -related deaths, and adverse cardiovascular events such as heart attack and stroke, through to 2018.
Almost a third (31%) of the participants reported taking regular fish oil supplements at the start of the study.
The association between fish oil use and reduced cardiovascular risks appeared to be stronger among those with high blood pressure.
These beneficial links between fish oil and heart health remained after accounting for the known effects of other factors such as age, sex, lifestyle habits, diet, medications, and other supplements.
Li ZH, Zhong WF, Liu S, Kraus VB, Zhang YJ, Gao X, Lv YB, Shen D, Zhang XR, Zhang PD, Huang QM, Chen Q, Wu XB, Shi XM, Wang D, Mao C. Associations of habitual fish oil supplementation with cardiovascular outcomes and all cause mortality: evidence from a large population based cohort study. BMJ. 2020 Mar 4;368:m456. doi: 10.1136/bmj.m456.