Omega-3 paradox: Study finds fish oil supplements boost first-time heart disease but slow an existing condition

29 May 2024 --- Researchers from various academic institutions in the US, China, Denmark and the UK conducted a large long-term cohort study into the regular use of fish oil supplements on the trajectory of cardiovascular disease. The study found that regular use could increase the risk of first-time heart disease and stroke but slow the progression of existing poor cardiovascular disease.

When they divided major adverse cardiovascular events into three individual diseases — heart failure, stroke and myocardial infarction — they found associations that suggest a mildly harmful effect between regular use of fish oil supplements and transitions from a healthy cardiovascular state to stroke.

Beneficial associations were found between regular use of fish oil supplements and transitions from atrial fibrillation to myocardial infarction, atrial fibrillation to death and heart failure to death.

The study enlisted 415,737 participants from the UK Biobank biomedical database, 55% of whom were women between 49 and 69. They were surveyed between 2006 and 2010 based on their dietary intake of oily and non-oily fish and fish oil supplements. The participants’ health was tracked until March 2021.

Purely observational
The researchers are adamant that no conclusions can be drawn about causal factors because this is an observational study in which no potentially influential information was available on the dose or formulation of the fish oil supplements. The results are not generalizable for different ethnicities either because the majority of the participants were white. The findings are published in the open-access journal BMJ Medicine.

The researchers note: “Regular use of fish oil supplements might have different roles in the progression of cardiovascular disease. Further studies are needed to determine the precise mechanisms for the development and prognosis of cardiovascular disease events with regular use of fish oil supplements.”

In-depth analysis showed that age, sex, smoking, consumption of non-oily fish, high blood pressure and use of statins and blood pressure-lowering drugs changed the associations observed. 

Regular use of fish oil supplements and the risk of transitioning from good health to heart attack, stroke or heart failure was 6% higher in women and in non-smokers. The protective effect of the supplements on the transition from good health to death was more significant in men and older participants.

During an average monitoring period of about 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 without atrial fibrillation or severe cardiovascular disease.

Progression of CVD during trial
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. And 2,436 of those with heart failure died, as did 2,088 of those who had had a stroke and 2,098 of those who had had a heart attack.

Roughly a third of the participants said they regularly used fish oil supplements. Alcohol intake and the ratio of oily to non-oily fish eaten were higher in this group, while the proportions of current smokers and those living in deprived areas were lower.A recent observational study looks at when fish oil supplements have a positive or negative influence on the progression of cardiovascular disease.

The findings indicated that regularly taking fish oil supplements had different roles in cardiovascular health, disease progression and death. Fish oil is a rich source of omega-3 fatty acids and is recommended as a dietary preventive to ward off the development of cardiovascular disease. However, the researchers explain that the evidence on how much protection it affords is inconclusive.

Meanwhile, interest in proactive and preventive measures for heart health is surging among a diverse demographic, as cardiovascular diseases remain the leading cause of death worldwide. Nutrition Insight spoke to several industry experts who confirmed that consumers are increasingly turning to nutraceuticals and dietary supplements for heart and cardiovascular health.

Collaborative research 
The scientists who set up this study practice at Sun Yat-Sen University, China; Saint Louis University, US; the Medical Research and Biometrics Centre, Fuwai Hospital, China; the National Centre for Cardiovascular Diseases, China; Peking Union Medical College, China; Liverpool Centre for Cardiovascular Science; the University of Liverpool; Liverpool Heart and Chest Hospital, UK and Aalborg University, Denmark.

They set out to estimate the associations between fish oil supplements and new cases of atrial fibrillation, heart attack, stroke, heart failure and death from any cause in those with no known cardiovascular disease. 

Furthermore, the researchers assessed the potential role of these supplements on the risk of progressing from good heart health to atrial fibrillation and then to major cardiovascular events, such as a heart attack or death.

For those with no known cardiovascular disease at the start of the monitoring period, regular use of fish oil supplements was associated with a 13% heightened risk of developing atrial fibrillation and a 5% heightened risk of having a stroke.

However, among those who had cardiovascular disease at the start of the monitoring period, regular use of fish oil supplements was associated with a 15% lower risk of progressing from atrial fibrillation to a heart attack and a 9% lower risk of progressing from heart failure to death.

Correlation between different studies
The findings confirm the results of several previous randomized controlled trials and meta-analyses. For example, the Long-Term Outcomes Study to Assess Statin Residual Risk with Epanova in High Cardiovascular Risk Patients with Hypertriglyceridaemia showed that consumption of 4 g a day of marine omega-3 fatty acids was associated with a 69% higher risk of new-onset atrial fibrillation in people at high risk of cardiovascular disease. 

Another meta-analysis of seven randomized controlled trials showed that marine omega-3 fatty acids supplement users had a higher risk of atrial fibrillation events.

Last year, the European Society of Cardiology, in collaboration with the University of Oxford, UK, presented staggering figures about the cost of cardiovascular diseases on European healthcare expenses, estimated at €282 billion (US$305 billion) from data collected and processed in 2021. The cost of general health care and long-term care alone amounts to €155 billion (US$168 billion).

By Inga de Jong