Omega-3 / Fish Oil
EPA and DHA for heart and brain health, with a real evidence gap between fatty fish and fish oil pills.
Not medical advice — check with a doctor before starting, especially if you take blood thinners or have a bleeding disorder.
How It Works
EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) are the two long-chain omega-3 fatty acids found in fatty fish and fish oil supplements — distinct from the shorter-chain ALA found in plant sources like flaxseed, which the body converts to EPA/DHA only inefficiently. EPA and DHA are incorporated into cell membranes throughout the body, including the heart and brain, and influence inflammation and triglyceride metabolism, which is the basis for most of the cardiovascular research below.
The Research
This is a supplement where the evidence is genuinely mixed, and the details of which study used what matter a lot.
Cardiovascular — a real split result: Bhatt DL, et al. "Cardiovascular Risk Reduction with Icosapent Ethyl for Hypertriglyceridemia" (REDUCE-IT), New England Journal of Medicine, 2019. In statin-treated patients with high triglycerides, 4g/day of a purified, prescription-only EPA formulation (icosapent ethyl) cut major cardiovascular events by 25% relative to placebo. It's worth being precise here: this trial used a high-dose prescription drug, not an over-the-counter fish oil supplement.Read the trial →
Manson JE, et al. "Marine n-3 Fatty Acids and Prevention of Cardiovascular Disease and Cancer" (VITAL), New England Journal of Medicine, 2019. In a general-population trial, a more typical 1g/day fish oil supplement showed no significant reduction in major cardiovascular events overall — though a secondary analysis found a benefit specifically in people who ate little fish to begin with.
Read the trial →
Cognitive function: evidence here is weaker still — several RCTs of DHA-rich fish oil have largely failed to improve cognition or slow decline in older adults with normal or mildly impaired cognition. If there's a benefit, it looks concentrated in earlier-stage decline, not a general brain-boosting effect for healthy adults.
Food vs. supplement — a documented gap: cohort studies pooling over a million participants associate higher fish consumption with meaningfully lower cardiovascular risk, a contrast with VITAL's null supplement result above. Fish oil isn't necessarily "the same thing in a pill" as eating fish — the fish itself may carry other nutrients or displace less healthy foods in the diet, and at least one large cohort has linked habitual fish oil supplement use to a small increase in atrial fibrillation risk in people without existing heart disease, which is worth knowing rather than assuming supplements are risk-free.
Typical Dosing
Per the NIH Office of Dietary Supplements, combined EPA+DHA intake up to 3g/day (including diet) is generally recognized as safe; doses above 5g/day aren't generally recommended without medical supervision due to a bleeding-risk signal at high intakes. Most OTC fish oil supplements provide 250mg–1,000mg combined EPA+DHA per serving — check the label rather than assuming a standard dose.
NIH Office of Dietary Supplements — Omega-3 Fatty Acids Fact Sheet →
Who Should Be Cautious
High-dose fish oil can increase bleeding risk, so anyone on blood thinners (warfarin, aspirin therapy) or with a bleeding disorder should talk to a doctor first. As above, one large cohort linked habitual supplement use to a modest increase in atrial fibrillation risk in people without pre-existing heart disease — a reason to treat high-dose, long-term use as something to discuss with a doctor rather than a default.