The study evaluates the relative safety and benefits of consuming pelagic fish during pregnancy, focusing on the relationship between mercury (Hg) and selenium (Se) concentrations in fish tissues and their potential impact on human health.
Background:Mercury is a heavy metal with well-documented toxic effects on human health and the environment. Fish is an excellent source of protein, rich in omega-3 fatty acids and essential nutrients. However, consuming certain fish species also exposes people to methylmercury, the most toxic form of mercury.
This heavy metal accumulates in fish, particularly predatory species like tuna, as it binds strongly to proteins in their tissues. The World Health Organization (WHO) ranks mercury among the ten most dangerous chemicals to human health. It can harm the central nervous system, with fetuses and young children being especially vulnerable. As a result, there are specific dietary recommendations for pregnant women regarding fish consumption.
On the other hand, the benefits of seafood consumption are observed in improved neurological health and development, as well as in protection of cardiovascular and ocular health. Increased seafood intakes are associated with reduced cancer incidence and diminished development of neurodegenerative diseases.
While public awareness has previously focused on health risks due Hg exposures (see the News below), advances in understanding emphasize the need for ensuring adequate intakes of seafoods. Several studies have shown, that far greater health risks accompany the nutritional deficits that arise from the inadequate seafood intakes. There are also numerous studies showing that several nutrients in seafood, including selenium, counteract the toxic effects of mercury as long as the mercury content is not higher than the selenium content.
A food safety index that assesses the risk of mercury contamination in fish is calculated from the Se and Hg content. A positive Health Benefit Value (HBV) indicates that the selenium content in the fish is sufficient to offset the harmful effects of mercury, making it safe to consume.
The new study:The objectives of the study include evaluating the Hg and Se content in ocean fish to establish their HBVs, and to provide a simple and reliable index for differentiating safe and beneficial ocean fish from those that may not provide these benefits.
The methods used in the study include analyzing the Hg and Se content in 15 species of ocean fish, and calculating their HBVs based on the molar ratio of Se to Hg. The results of the study show that 14 out of 15 species of ocean fish have a positive HBV, indicating that they are safe to eat during pregnancy, while only mako shark has a negative HBV, indicating that its consumption should be minimized.
The conclusions of the study are that ocean fish are a rich source of selenium, which can prevent the negative effects of mercury toxicity, and that consuming ocean fish can provide substantial health benefits.
The original publication
Nicholas V. C. Ralston, J. John Kaneko, Laura J. Raymond,
Selenium, Mercury, and Health Benefit Values of Pelagic Ocean Fish of the Central North Pacific. Fishes, 10 (2025) 158.
DOI: 10.3390/fishes10040158
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last time modified: April 9, 2025
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