Reprinted from permission from World at Large

A breakthrough in packaged tuna preparation has been found to reduce mercury content in the fish by 35%.

Consumption of tuna has long been limited, especially by pregnant women and nursing mothers, for the known fact that the fish accumulates mercury throughout its life.

If canned with a water solution containing high amounts of the amino acid cysteine, the tuna meat was found to have 35% less mercury than normal canned tuna.

It’s one of a variety of breakthrough packaging inventions collectively referred to as “active packaging” which reacts with the food being preserved to help increase its shelf-life and nutrient density.

GNN has reported on some packaging that also contains elements that interact with the food to create a vivid color that will warn consumers if the food inside has spoiled.

In this case, the cysteine in the tuna can draw out the mercury and prevent it from binding to human tissues.

“Our study shows that there are alternative approaches to addressing mercury contamination in tuna, rather than just limiting consumption. Our goal is to improve food safety and contribute to enhanced human health, as well as to better utilize food that is currently under certain restrictions,” says Mehdi Abdollahi, Associate Professor at the Department of Life Sciences at Chalmers and coordinator of a project called Detoxpak.

In science, sometimes disagreements can emerge when comparing empirical truth with observed effects. For example, mercury exists in tuna—of that there can be no doubt—but a growing mountain of evidence suggests that it’s either too low to affect the health of even a fetus, or that there’s something in tuna that’s already protecting us from the maleffects of mercury.

Tuna’s seachange

Take for example a long-term monitoring study from 2001 to 2018 which looked at mercury concentrations in the flesh of three tuna species in the Pacific. The study found consistent mercury levels independent of the increasing amounts of mercury in the ocean due to the increase in coal burning among the nations bordering the research area.

In other words, this study casts significant doubt on the idea that mercury enters the fish through environmental contamination.

Tuna meat is rich in selenium, an irreplaceable and essential nutrient for early childhood cognitive development. Selenium also happens to be part of why cysteine works to reduce mercury content in the new tuna packaging: selenium and cysteine form the amino acid selenocysteine, which methylmercury, the compound found in tuna flesh, binds to in the can (and in the human brain) but since the fetal brain doesn’t contain reserves of selenium, it has no natural defense against methylmercury inhibiting selenocysteine’s vital activities in the brain.

A 2024 study however looked at mercury and selenium concentrations in the umbilical cords of fetuses in Hawaiian mothers who ate lots of seafood containing both molecules.

The cord blood samples exceeded the EPA’s mercury toxic reference level of 5.8 ppb, but selenium concentrations were orders of magnitude higher, thus conferring, in theory, all the necessary protective elements to prevent that mercury from affecting the fetus.

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The study stated the finding “clarifies the reasons for the contrasting findings of certain early studies,” namely those listed in a systemic review issued by the National Academy of Science called ‘The Role of Seafood Consumption in Child Growth and Development.’

The review lists numerous studies and meta-analyses that show consumption of seafood known to contain mercury is associated with mostly positive neurodevelopmental outcomes in children, with one study showing an associated increase in IQ of 2 to 5 points. Others report a mix of positive and negligible associations between seafood consumption in young children and infants and neurodevelopmental outcomes.

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Another meta-analysis identified by the review identified 29 studies representing 24 unique cohorts. Of the 29 studies, 24 reported beneficial outcomes associated with maternal seafood consumption and neurocognition on some or all the tests administered to children. Based on their analysis, the authors reported moderate and consistent evidence for an association of consumption of a broad range of amounts and types of commercially available seafood during pregnancy with improved neurocognitive development in the offspring as compared to not consuming seafood.

There’s certainly every reason to remove mercury from the human diet, but it looks like the science behind the threat of seafood-born mercury is undergoing a seachange.

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