Little agreement exists as to whether low-level mercury (Hg) exposure causes damage to the central nervous system in adults. Although eating fish is associated with intake of methylmercury, researchers in this field have generally thought that the beneficial effects of a diet rich in long-chain, n-3 fatty acids (N3FA) can outweigh the cognitive neurotoxicity of mercury. This study clarifies the impact of Hg and intake of seafood on cognition.
The study was a retrospective, cross-sectional analysis, published in Integrative Medicine a Clinicians Journal. The research team performed the study at the Carillon Outpatient Center in St Petersburg, Florida. Participants were 384 men and women, primarily corporate executives, who were attending an all-day comprehensive physical evaluation.
Outcome Measures / At participants’ initial evaluations, the research team made measurements of body 
composition, evaluated cardiovascular status, assessed fitness, documented dietary habits (including specific types of seafood intake), and performed laboratory measures, including tests for whole- blood Hg (BHg). The team tested each subject using CNS Vital Sign, which is a computerized, neurocognitive test battery comprised of seven familiar neuropsychological tests that generate 10 independent scores.
Results: Participants’ average BHg level was 7.2 μg/L. The relationship between Hg and cognitive performance was quadratic. Compared to participants with Hg levels in the 5 μg/L–to–14 μg/L range, participants with high Hg levels tested 4% to 5% lower for complex-information processing (CIP), and participants with normal Hg levels tested 2% lower. An increase in N3FA was associated with a linear improvement in CIP up to three servings of fish per week. A direct linear relationship existed between N3FA intake and BHg levels, and the interaction of Hg and N3FA intake accounted for the relationship between mercury levels and cognition.
Conclusions / Excessive seafood intake, particularly large-mouth fish, elevates Hg levels and causes cognitive dysfunction, especially for mercury levels ≥15 μg/L. Higher N3FA intake initially is associated with improved cognitive function, but rising Hg levels ultimately overwhelm the moderating effect of N3FA intake.
