Fish oil supplements are often praised for their heart-protecting benefits, but new research from Finland suggests that their effects can vary greatly between individuals—even among healthy people.
The study, published in JCI Insight, reveals that the body’s metabolism plays a major role in determining how well fish oil works to prevent cardiovascular disease.
The research team, led by Professor Katariina Öörni from the University of Helsinki and the Wihuri Research Institute, focused on a key omega-3 fatty acid called eicosapentaenoic acid, or EPA.
EPA is found in fish oil and has been shown to help people with high cholesterol or heart disease by improving blood fat levels and lowering inflammation. However, its effects on healthy individuals have not been well understood.
To explore this, the researchers gave 38 healthy volunteers very high doses of EPA supplements and monitored them before, during, and after the supplementation period.
They analyzed the participants’ blood to see how EPA changed the composition of lipoproteins—the molecules that transport fats through the bloodstream.
The results showed that EPA was absorbed efficiently by everyone, causing blood levels of the fatty acid to rise sharply during supplementation.
However, these levels dropped quickly once participants stopped taking the supplements, indicating that EPA’s effects may be short-lived. Interestingly, people who started with lower natural levels of EPA in their blood experienced the strongest responses.
Despite the overall increase in EPA, each participant’s blood fat profile remained distinct. “Every person has their own unique ‘lipid fingerprint’—a personal mix of fats and lipoproteins in their blood,” said Professor Öörni.
“Even though the supplements worked for everyone, their individual lipid fingerprints didn’t disappear.”
The study also found that EPA can improve the quality of blood fats and reduce the tendency of lipoproteins to stick to artery walls—a key process in the development of atherosclerosis, or the buildup of fatty plaques that can lead to heart disease.
These findings suggest that fish oil could benefit not only people with heart conditions but also healthy individuals by improving early markers of cardiovascular health.
However, the researchers caution that this was a short-term study, so the long-term effects of EPA on heart health remain unknown. More research is needed to determine how sustained supplementation might influence metabolism and disease prevention over time.
Doctoral researcher Lauri Äikäs, one of the study’s authors, said that the wide variation in results among participants was surprising. “EPA clearly affects everyone, but in very different ways,” he explained.
“And because the effects fade quickly, it’s reassuring to know that any potential side effects would likely disappear just as fast.”
Next, the team plans to study how EPA influences inflammation by examining its effects on immune cells and molecules that help control the body’s inflammatory response.
As Professor Öörni noted, “It’s fascinating to see how something as simple as diet can change the makeup of our blood fats—and how unique each person’s response really is.”
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