Fish oil may increase risk of early heart disease and stroke

Regular use of fish oil supplements may increase the risk of primary heart disease and stroke in people with good cardiovascular health, but slow the progression of existing cardiovascular problems system and reduce the risk of death. These are the results of 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, data on the degree of its protection is ambiguous, the researchers explain.

To strengthen the evidence base, researchers sought to evaluate the association between fish oil supplements and new cases of atrial fibrillation; myocardial infarction, stroke and heart failure; and mortality from any cause in those without known cardiovascular disease.

They assessed the possible role of these supplements in the risk of progression from good cardiovascular health (primary stage) to atrial fibrillation (secondary stage), to major cardiovascular events such as myocardial infarction (tertiary stage), and to death ( final stage).

The researchers used data from 415,737 UK Biobank study participants (55% women), aged 40 to 69, who were interviewed between 2006 and 2010 to collect baseline information. This included their usual consumption of fatty and lean fish and fish oil supplements.

Participants' health was tracked until the end of March 2021 or until their death, whichever occurred first, using medical record data.

Nearly a third (130,365; 31.5%) of participants said they regularly used fish oil supplements. This group included a higher percentage of older and white people, as well as women. Alcohol consumption and the ratio of fatty to lean fish were also higher, while the percentage of smokers and those living in deprived areas was lower.

During a mean 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 serious 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 who had 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 study results.

For those with no known cardiovascular disease at baseline, regular use of fish oil supplements was associated with a 13% increased risk of atrial fibrillation and a 5% increased risk of stroke.

However, among those with cardiovascular disease at baseline, 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 in-depth analysis found that age, gender, smoking, consumption of lean fish, 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 going from good health to heart attack, stroke or heart failure was 6% higher in women and 6% higher in non-smokers. 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. No potentially relevant information was available on either the dosage or composition of fish oil supplements. And because most 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 various roles in the progression of cardiovascular disease. Further research is needed to determine the precise mechanisms behind the development and prognosis of cardiovascular disease with regular use of fish oil supplements."