Fish oil, rich in omega-3 fatty acids like EPA and DHA, has been investigated for its effects on cognitive function, including concentration and attention. Scientific interest in fish oil's role in brain health stems from the fact that DHA is a major structural component of neuronal membranes. Several observational studies have linked higher dietary intake of omega-3s with better cognitive performance. Randomized controlled trials (RCTs) in both children (especially those with attention-deficit/hyperactivity disorder, or ADHD) and adults have yielded mixed results, with some showing modest improvements in attention and concentration, and others finding no significant benefit compared to placebo.

A 2012 meta-analysis in PLoS ONE reviewing RCTs in children with ADHD found small but significant improvements in attention with omega-3 supplementation. However, these effects were modest, and not all studies showed benefit. In healthy adults and older populations, some studies report minor improvements in measures of attention and working memory, but large-scale reviews and systematic analyses generally conclude that the evidence is inconsistent and not robust enough to recommend fish oil as a treatment for poor concentration in the general population.

In summary, while there is biological plausibility and some scientific evidence for fish oil's benefit in supporting concentration, especially in specific populations, the overall quality and consistency of evidence is limited. More high-quality, large-scale studies are needed to establish clear efficacy.