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Regular intake of fish oil supplements might paradoxically elevate the risk of initial heart disease and stroke in people with good cardiovascular health.

Nonetheless, it may also mitigate the progression of existing cardiovascular ailments and reduce mortality risks, as highlighted in a comprehensive long-term study released on May 21 in the open-access journal BMJ Medicine.

Fish oil, renowned for its omega-3 fatty acid content, is often endorsed as a preventive measure against cardiovascular disease. However, the actual protective benefits it confers remain uncertain, note the researchers.

To bolster the evidence base, the researchers aimed to assess the associations between fish oil supplements and incidents of atrial fibrillation; heart attack, stroke, and heart failure; and all-cause mortality in individuals without known cardiovascular disease.

They examined the potential impact of these supplements on the progression from good cardiovascular health (primary stage) to atrial fibrillation (secondary stage), major cardiovascular events like heart attack (tertiary stage) and mortality (end stage).

The study encompassed 415,737 participants from the UK Biobank (55% women) aged 40-69, surveyed between 2006 and 2010 to collect baseline data, including dietary habits regarding oily and non-oily fish as well as fish oil supplements, SciTech Daily reported.

Participants' health status was monitored until March 2021 or death, utilizing medical records data.

Of the participants, nearly a third (130,365; 31.5%) reported regular fish oil supplement usage. This subset comprised a higher proportion of older individuals, White participants, and women. Notably, alcohol intake and consumption of oily fish were higher among supplement users, while smoking rates and deprivation levels were lower.

Over an average follow-up period of almost 12 years, 18,367 individuals developed atrial fibrillation, 22,636 experienced a heart attack/stroke or developed heart failure, and 22,140 died-among whom 14,902 had no atrial fibrillation or serious cardiovascular disease.

Among those progressing from good cardiovascular health to atrial fibrillation, 3,085 developed heart failure, 1,180 had a stroke, and 1,415 experienced a heart attack. Additionally, 2,436 individuals with heart failure passed away, alongside 2,088 stroke survivors and 2,098 heart attack survivors.

The study findings revealed varying roles of regular fish oil supplement usage in cardiovascular health, disease progression, and mortality.

For individuals without known cardiovascular disease at baseline, regular fish oil supplement intake was associated with a 13% higher risk of developing atrial fibrillation and a 5% higher risk of stroke occurrence.

Conversely, among those with pre-existing cardiovascular disease, regular fish oil supplement usage was linked to a 15% lower risk of transitioning from atrial fibrillation to heart attack and a 9% lower risk of progression from heart failure to mortality.

Further analysis showed that factors such as age, sex, smoking status, consumption of non-oily fish, hypertension, and medication use altered the observed associations.

The association between regular fish oil supplement usage and transitioning from good cardiovascular health to heart attack, stroke, or heart failure was 6% higher in women and non-smokers. Moreover, the protective effect against transitioning to mortality was more pronounced in men (7% lower risk) and older participants (11% lower risk).

As this study is observational, causal relationships cannot be inferred, caution the researchers. Additionally, information regarding supplement dosage and formulation was unavailable, and the predominantly white participant cohort may limit generalizability to other ethnicities.

Despite these limitations, the researchers emphasized the need for further investigation into the distinct roles of fish oil supplements in cardiovascular disease progression.

"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," the authors concluded.