However, the research highlights that the supplements could also be beneficial, slowing the progression of poor cardiovascular health and lowering the risk of death.
These mixed findings were part of a large-scale study in the United Kingdom of 415,737 participants and was funded by the Bill and Melinda Gates Foundation.
“When we divided major adverse cardiovascular events into three individual diseases (i.e, heart failure, stroke and myocardial infarction), we found associations that could suggest a mildly harmful effect between regular use of fish oil supplements and transitions from a healthy cardiovascular state to stroke," the researchers wrote. "Our findings are in agreement with the results of several previous randomized controlled trials and meta-analyses."
Inadequate studies
The current study also relied on previous analysis to bolster the researchers’ claims. Some earlier studies had restricted participants with a specific cardiovascular disease or a high risk of the disease, while others analyzed databases of healthy populations.
“All of these factors might preclude direct comparison of the effects of omega-3 fatty acids on atrial fibrillation events or on further deterioration of cardiovascular disease,” the researchers wrote. “Few studies have fully characterized specific cardiovascular disease outcomes or accounted for differential effects based on the complex disease characteristics of participants.”
They added that no study focused on the progressive nature of cardiovascular diseases, including the path from healthy status to atrial fibrillation and then to major adverse cardiovascular events to death.
The researchers noted that “clarifying this complex pathway in relation to the detailed progression of cardiovascular diseases would provide substantial insights into the prevention or treatment of future disease at critical stages.”
Study details
To address this gap in evidence, the researchers relied on the UK Biobank, a cohort study with more than half a million UK residents between the ages of 40 and 69 at recruitment. Participants included in the fish oil research were initially assessed as part of a baseline survey between 2006 to 2010 where personal, socioeconomic, lifestyle, diet and disease information were collected. Status of fish oil supplement use was also recorded, and the researchers measured biochemistry markers from serum samples collected at baseline. Participants were followed from study recruitment to death, or to the end date of the study in March. One third of the participants regularly took fish oil. The control group consisted of non-users of omega-3s.
The results showed that regular consumption of fish oil supplements for those without cardiovascular disease at the beginning of the study was associated with a 13% increased risk of developing atrial fibrillation and a 5% likelihood of having a stroke.
For participants with cardiovascular disease at the beginning of observation, consistent use of omega-3s was linked to a 15% reduction of atrial fibrillations to heart attack progression. There was an associated 9% reduced risk of heart failure to death.
Curiously, women who started off in good health while taking fish oil were 6% more likely to experience heart attack, stroke or heart failure, the study reported.
Study limitations
The researchers suggest the study had some gaps in knowledge. As it was an observational study, no causal relationships can be inferred from the findings. Additionally, the researchers did not account for dose and formulation of the fish oil supplements so they could not assess dose dependent effects. When it came to reviewing hospital inpatient data for atrial fibrillation events, the researchers may not have accounted for events caused by surgery, trauma or other conditions. This lack of evaluation could mean an “underestimation of the true risk” because undiagnosed atrial fibrillation is common, the researchers said.
They added: “Further studies are needed to determine whether potential confounders modify the effects of oil fish supplements and the precise mechanisms related to the development and prognosis of cardiovascular disease events.”
Harry Rice, PhD, vice president of regulatory and scientific affairs at GOED, said the findings are worthy of further exploration but that they were also difficult to reconcile.
“They don’t necessarily align with past results,” he said. “As always, it’s important to examine the totality of the scientific evidence, rather than focus on a single study. With that approach in mind, individuals should continue to eat fatty fish and take their fish oil (or other EPA/DHA-rich sources) supplements.”
Cardiovascular disease is the leading cause of death globally. Fish oil, a source of omega 3 fatty acids containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), is recommended to prevent cardiovascular disease, the researchers noted.
They added, “The UK National Institute for Health and Care Excellence recommends that people with or at high risk of cardiovascular disease consume at least one portion of oily fish a week, and the use of fish oil supplements has become popular in the UK and other western countries in recent years.”
Source: BMJ Medicine
doi: 10.1136/bmjmed-2022-000451
“Regular use of fish oil supplements and course of cardiovascular diseases: prospective cohort study”
Authors: Ge Chen et al.
