The effects of methylmercury exposure in humans as a result of excessive fish consumption can include neurodevelopmental deficits, poorer cognitive performance and increased rates of cardiovascular disease.

The study also notes that higher levels of methylmercury can be detrimental to the positive effects of omega-3 fatty acids, which are known to reduce cholesterol levels, reduce the risk of some cancers and incidence of heart disease, blood pressure, stroke, and pre-term delivery.

Over 1,200 people were interviewed about their consumption of sushi and other fish products and mercury levels in sushi samples were analysed from the USA. The study noted that 92% of participants ate an average of 5 fish and fish-sushi meals per month and the top 10% of all participants from across all ethnic groups exceeded the Center for Disease Control Minimal Risk Level and the World Health Organization Provisional Tolerable Weekly Intake of methylmercury.

The study further notes that large tuna, such as the Atlantic Bluefin or Bigeye, which are prized for sushi contain the highest mercury levels and that the demand for high-grade tuna for sushi has placed the species into jeopardy by overfishing.

Sushi made with eel, crab, salmon and kelp were found to have lower levels of methymercury.