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Britons who took fish oil supplements -- and not the prescription pharmaceutical-grade kind -- lived longer on average and were less likely to develop cardiovascular disease (CVD) years down the line, according to a large prospective cohort study.

U.K. Biobank participants who reported habitual supplementation with store-bought omega-3 fatty acid-rich fish oil pills had better outcomes over 8 to 9 years of follow-up:

• All-cause mortality: adjusted HR 0.87 (95% CI 0.83-0.90)
• CVD mortality: adjusted HR 0.84 (95% CI 0.78-0.91)
• Overall CVD events: adjusted HR 0.93 (95% CI 0.90-0.96)

The inverse relationship between fish oil supplements and CVD risk persisted after adjustment for sex, age, income, diet, and alcohol consumption, and other variables, according to Chen Mao, MD, PhD, of Southern Medical University in Guangzhou, China, and colleagues reporting online in .

"Our findings are in accordance with the results of several previous studies that found that fish oil supplementation is associated with a lower risk of CVD outcomes," they noted.

Yet whether omega-3 fatty acid supplementation truly has benefit in CVD prevention has been an area fraught with uncertainty.

In 2018, the VITAL randomized trial found no reduction in major cardiovascular events among those assigned omega-3 fatty acids instead of placebo. There was a signal that the intervention could cut rates of MI and coronary heart disease, however.

That year, the REDUCE-IT group showed that Amarin's icosapent ethyl (Vascepa) -- a prescription high-dose fish oil product that recently had its cardiovascular risk reduction indication approved by the FDA -- did, in fact, work for primary and secondary CVD prevention in a higher-risk population with elevated triglycerides.

Contradictory evidence in the fish oil field may be attributed to insufficient power of certain studies and the variations in dose tested, Mao and colleagues suggested.

"Owing to its low cost, lack of fishy taste or smell, convenience of use, and mild side effects, fish oil supplementations could be an inexpensive, quick, and safe way of increasing an individual's omega-3 fatty acid intake," according to them.

The study included 427,678 adults ages 40 to 69 with no CVD or cancer at baseline. The group was 55.1% women, with a mean age of 55.9 years.

As part of their participation in the U.K. Biobank, individuals completed a questionnaire and a face-to-face interview, provided biological samples, and underwent a series of physical measurements.

Fish oil's association with reduced mortality was especially seen among men (P for interaction=0.010) and current smokers (P for interaction=0.009). On the other hand, the greatest lowering in CVD events was seen in people with prevalent hypertension (P for interaction=0.005), Mao's team showed.

Just under one in three people said they took fish oil supplements regularly.

Compared to non-users, this group was generally older and more likely to be female, not currently smoking, and physically active. Such individuals also reported eating fish more regularly and taking antihypertensive drugs, aspirin, vitamin supplements, and mineral and other dietary supplements.

Residual confounding remained a potential limitation of the observational study, Mao's team acknowledged. Furthermore, the authors did not have more detailed information (dose, formulation, duration of use) on the fish oil supplementation reported, and what they did have was self-reported.

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