A large-scale analysis of UK Biobank participants found that higher blood circulating levels of omega-3 fatty acids were associated with a significantly lower risk of developing atrial fibrillation (AFib). The findings, published in the Journal of the American Heart Association, come amid mixed evidence about the impact of fish oil supplementation on heart rhythm.

The large-scale biomarker-based study analyzed data from hundreds of thousands of participants in the UK Biobank. In total, 261,108 participants had data on plasma omega-3 levels, and 466,169 reported fish oil supplement usage. Individuals with higher omega-3 levels had a lower incidence of AFib over a median 12.7 years of follow-up, compared to those with a lower omega-3 status. Meanwhile, when adjusted for confounding effects of age in the statistical models, fish oil supplementation showed no association with AFib, contrary to prior analyses conducted on the UK Biobank.

“These results reinforce that it’s the physiologic status of omega-3 in the blood, not simply supplementation per se, that correlates with AF risk. In properly adjusted models, supplement use showed no increase in AF risk,” said Bill Harris, PhD, senior investigator of the paper and president of the Fatty Acid Research Institute (FARI).

“From a clinical standpoint, these findings help clarify an important misconception,” Harris added. “When we look at objectively measured blood omega-3 levels, higher status is associated with lower risk of atrial fibrillation—not higher. This reinforces the importance of evaluating physiology, not assumptions about supplements. Concerns raised by earlier reports linking fish oil use to atrial fibrillation were likely driven by methodological limitations. When age is modeled appropriately, fish oil supplement use does not increase atrial fibrillation risk.”

“This very large, methodologically sound and statistically robust study finds that higher omega-3 blood levels correlate with lower risks for atrial fibrillation during long-term follow-up. This is in line with other recent studies our group has done, which show that omega-3 in doses typically achieved with consumption of fish/seafood and/or omega-3 over-the-counter supplements reduces risk of AFib. The only signal for increased AFib risk comes in people treated with a very high-dose omega-3, such as pharmacologic, prescription-strength omega-3 products, used in people at high risk for AFib. For the vast majority of people, omega-3 intake is a safe and effective nutrient for supporting long-term heart and brain health.”