Do fish oil supplements protect the heart and brain, and why do some studies suggest an increased risk of atrial fibrillation?

“Fish oil” covers products with different ingredients, doses and trial results. REDUCE-IT found that prescription icosapent ethyl, a purified EPA product, reduced cardiovascular events in selected statin-treated patients with elevated triglycerides and high cardiovascular risk. That result cannot simply be transferred to an over-the-counter capsule. STRENGTH, which tested a high-dose EPA/DHA formulation in another high-risk population, did not reduce its primary cardiovascular endpoint. Lowering triglycerides or containing omega-3 fats is therefore not sufficient evidence that any particular product prevents heart attacks.[1][2]

Atrial fibrillation is part of the tradeoff: these high-dose trials reported more atrial fibrillation events with active treatment, although the measurements and populations differed. This does not mean that ordinary fish consumption carries the same risk, or that every supplement user will develop an arrhythmia. It does mean the indication and baseline risk matter, especially with previous AF. Brain protection is a separate question: in the AREDS2 randomized trial, omega-3 supplementation did not slow cognitive decline over five years in the studied older population. Heart and memory claims should each be supported by their own outcome evidence.[1][2][3]