Omega-3 fats

For adults, oral EPA and DHA have the clearest evidence for changing blood lipids, especially triglycerides. That is a laboratory outcome, not the same as preventing a heart attack. A 2024 meta-analysis of 18 randomized trials involving 134,144 adults found modest reductions in several cardiovascular outcomes, including heart attack and cardiovascular death, but the studies used different omega-3 preparations and included both primary and secondary prevention populations.

The practical conclusion is narrower than many supplement labels suggest. Omega-3s may be useful in selected adults, particularly when triglycerides are elevated or cardiovascular risk is already being managed, but the evidence does not show that every over-the-counter fish-oil or algal-oil product provides the same protection.[5][4]

In an analysis of 11 randomized trials involving 485 healthy adults without coronary heart disease, algal-oil DHA lowered triglycerides by about 0.20 mmol/L on average. It also raised HDL cholesterol, often described as “good” cholesterol, but raised LDL cholesterol as well. The participants were healthy and the study tested algal DHA, so these findings should not be extended automatically to adults with very high triglycerides or to mixed fish-oil products.

EPA and DHA are long-chain omega-3 fats. They become part of cell membranes and are used to make signaling molecules, which helps explain why they can affect lipid handling and other biological processes. A plausible mechanism, however, is not proof that a supplement will prevent disease in a particular person.[4][1]

The 2024 meta-analysis reported lower risks of coronary revascularization, heart attack, and cardiovascular death among people randomized to EPA or EPA plus DHA compared with controls. The pooled relative risks were about 10% lower for revascularization, 11% lower for heart attack, and 8% lower for cardiovascular death. These are relative differences across trials, not a prediction of an individual’s absolute benefit.

The apparent benefit was stronger in trials using EPA alone than in trials using combined EPA and DHA. That comparison is informative but not definitive. The analysis also found meaningful variation between studies for revascularization, and its authors noted that the roles of specific molecules and different prevention settings still need research. A trial result for one purified or concentrated preparation should not be treated as proof for all retail products.[5]

DHA is especially abundant in the brain and retina, so a cognitive benefit is biologically plausible. Human outcome evidence is less convincing. A 2026 network meta-analysis of randomized trials in healthy older adults and people with mild cognitive impairment found domain-specific signals for DHA, including memory and processing speed, but the overall pattern was not universal cognitive enhancement.

The review also reported that some rankings changed in sensitivity analyses, particularly for smaller studies, shorter interventions, and different participant characteristics. This means the findings are useful for generating hypotheses, not for promising better memory to healthy adults. The review excluded people with diagnosed dementia, so its results do not answer whether omega-3 supplements treat dementia.[6]

A capsule’s total “fish oil” weight can be misleading because only part of that weight may be EPA and DHA. The chemical form also affects how the body handles the oil. In a randomized crossover study of eight female volunteers, free-fatty-acid forms produced higher blood levels than triglyceride forms, while ethyl esters produced lower levels; free fatty acids were less well tolerated, with eructation, or belching, as the main reported side effect.

The formulation story is not settled. In a separate human meal study of five adults with normal lipid levels, ethyl esters and triglycerides produced similar omega-3 responses when equivalent amounts of fat were given. These small, short pharmacokinetic studies measured blood levels rather than cardiovascular outcomes. They show why formulation deserves attention, but they do not prove that one form prevents more disease or causes fewer clinically important adverse effects. The evidence supplied here also does not provide a reliable pooled estimate of serious bleeding risk, so people using medicines that affect clotting or preparing for a procedure should discuss the product with a clinician.[3][2]