Eating fish, particularly oily fish as part of a Mediterranean dietary pattern, is associated with a lower risk of cardiovascular disease and possibly better brain health. Fish as a standalone food does not show a proven protective effect in all studies, however, and for pregnant women mercury exposure is a relevant risk.
Eating fish, particularly oily fish such as salmon, mackerel and tuna, is associated in multiple studies with a lower risk of cardiovascular disease and better brain health. The protective effect is largely attributed to the omega-3 fatty acids DHA and EPA. These compounds prompt the body to produce anti-inflammatory signalling molecules, in contrast to omega-6 fatty acids (found in sunflower and corn oil), which tend to promote more inflammation (PMID 29715470, 31521398).
For the heart, the results are mixed. Epidemiological research suggests that 200 mg of DHA per day from fish may reduce the risk of sudden cardiac death by approximately 50% (PMID 10479465). A large prospective study in the UK Biobank (118,469 participants, followed for over 9 years) found that people who ate the most fish as part of a healthy dietary pattern had 14% fewer cardiovascular events, with fish being one of the most strongly contributing food groups (PMID 39208450). Set against these positive findings is a large American cohort study (nearly 30,000 participants, followed for 19 years), which found no significant association between fish consumption in itself and the risk of cardiovascular disease or total mortality (HR 1.00; PMID 32011623). Fish as a standalone food therefore has no proven protective effect.
The strongest evidence for cardiovascular protection comes not from fish alone, but from the Mediterranean diet as a whole, of which fish is one component. Large randomised trials such as PREDIMED, Lyon Heart and CORDIOPREV show that this overall dietary pattern genuinely reduces cardiovascular disease and mortality (PMID 38336153, 25447615). The lesson is therefore: fish in the context of a varied, plant-rich diet has the most evidence behind it, not fish as a magic food in its own right.
For the brain, DHA is particularly relevant: this omega-3 fatty acid is preferentially taken up by the brain and is essential for the development and maintenance of brain tissue. Deficiencies in DHA have been associated in multiple studies with cognitive decline in older adults and with the occurrence of sporadic Alzheimer's disease (PMID 10479465, 31521398). The evidence here is, however, largely based on epidemiology and animal models. Large-scale randomised trials in humans demonstrating that eating fish genuinely prevents dementia are still lacking.
An important safety point: fish can contain mercury, especially large predatory fish such as tuna, swordfish and shark. For pregnant women, excessive fish consumption is therefore not an unconditional recommendation; mercury toxicity can be harmful to the developing brain of the unborn child (PMID 31521398). The general recommendation is: two portions of fish per week, preferably smaller oily fish species, is safe for most people and potentially beneficial.
Evidence consists of observational cohort studies (including the UK Biobank with 118,469 participants and an American cohort with approximately 30,000 participants), mechanistic studies on omega-3 fatty acids, and randomised trials (PREDIMED, Lyon Heart, CORDIOPREV) for the Mediterranean diet as a whole. Those trials concern the overall dietary pattern, not fish separately. There are no large randomised trials specifically examining fish consumption and cognition in humans.