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Fish oil may increase the risk of first heart disease and stroke
Last reviewed: 02.07.2025
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Regular use of fish oil supplements may increase the risk of new heart disease and stroke in people with good cardiovascular health, but slow the progression of existing cardiovascular problems and reduce the risk of death, according to a large long-term study published in BMJ Medicine.
Fish oil is rich in omega-3 fatty acids and is recommended as a dietary measure to prevent cardiovascular disease. However, the evidence on the extent of its protection is mixed, the researchers explain.
To strengthen the evidence base, the researchers sought to assess the association between fish oil supplements and new cases of atrial fibrillation; myocardial infarction, stroke, and heart failure; and all-cause mortality in those without known cardiovascular disease.
They assessed the possible role of these supplements in the risk of transition from good cardiovascular health (primary stage) to atrial fibrillation (secondary stage), to major cardiovascular events such as myocardial infarction (tertiary stage), and to death (end stage).
The researchers used data from 415,737 UK Biobank participants (55% women), aged 40 to 69, who were interviewed between 2006 and 2010 to collect baseline information. This included their usual intake of oily and lean fish and fish oil supplements.
Participants' health was monitored until the end of March 2021 or until their death, whichever came first, using medical record data.
Almost a third (130,365; 31.5%) of participants said they regularly used fish oil supplements. This group included a higher proportion of older people, white people and women. Alcohol consumption and the ratio of oily to lean fish were also higher, while the percentage of smokers and those living in deprived areas was lower.
During a median follow-up of nearly 12 years, 18,367 participants developed atrial fibrillation, 22,636 had a heart attack/stroke or developed heart failure, and 22,140 died—14,902 of them without atrial fibrillation or major cardiovascular disease.
Among those who progressed from good cardiovascular health to atrial fibrillation, 3,085 developed heart failure, 1,180 had a stroke, and 1,415 had a heart attack. Of those with heart failure, 2,436 died, as did 2,088 of those who had a stroke and 2,098 of those who had a heart attack.
Regular use of fish oil supplements had various roles in cardiovascular health, disease progression and death, according to the study results.
For those without known cardiovascular disease at the start of follow-up, regular use of fish oil supplements was associated with a 13% increased risk of developing atrial fibrillation and a 5% increased risk of stroke.
However, among those who had cardiovascular disease at the start of follow-up, regular use of fish oil supplements was associated with a 15% reduced risk of progression from atrial fibrillation to heart attack and a 9% reduced risk of progression from heart failure to death.
A more detailed analysis showed that age, sex, smoking, lean fish consumption, high blood pressure, and use of statins and blood pressure-lowering drugs modified the observed associations.
Regular use of fish oil supplements and the risk of transition from good health to heart attack, stroke, or heart failure was 6% higher in women and 6% higher in nonsmokers. The protective effect of these supplements on the transition from good health to death was greater in men (7% reduced risk) and older participants (11% reduced risk).
As the researchers note, this is an observational study, so no conclusions can be drawn about causal factors. There was no potentially relevant information available about the dosage or composition of the fish oil supplements. And because most of the participants were white, the results may not apply to people of other ethnic groups.
But they conclude: "Regular use of fish oil supplements may have different roles in the progression of cardiovascular disease. Further research is needed to determine the exact mechanisms of cardiovascular disease development and prognosis with regular use of fish oil supplements."