Evidence Level
Fish oil has the deepest evidence base of any nutritional supplement. The REDUCE-IT trial (Bhatt et al., 2019, NEJM) is the landmark study: 8,179 statin-treated patients with elevated triglycerides randomized to 4g icosapent ethyl (purified EPA) or placebo showed a 25% reduction in major adverse cardiovascular events — the first supplement trial to demonstrate hard cardiovascular endpoint reduction at this magnitude. A 2020 Cochrane review by Abdelhamid et al. analyzed 86 RCTs and confirmed omega-3s reliably reduce triglycerides and may slightly reduce coronary heart disease events and mortality, though effects on total mortality were less clear. For depression, Liao et al. (2019) meta-analyzed 26 RCTs and found significant benefit, particularly with EPA-dominant formulations at doses above 1g/day. Calder (2017) elucidated the anti-inflammatory mechanisms: EPA and DHA compete with arachidonic acid for COX-2/LOX enzymes and generate specialized pro-resolving mediators (resolvins, protectins, maresins) that actively resolve — rather than merely suppress — inflammation. Goldberg & Katz (2007) meta-analyzed 17 RCTs showing significant joint pain reduction in inflammatory arthritis. The evidence for cognitive decline prevention in healthy adults is weaker, though DHA is a structural component of brain cell membranes. Bioavailability research shows re-esterified triglyceride (rTG) form is 70% better absorbed than ethyl esters.