The heavy metal called mercury is toxic in high enough doses, produced naturally in the earth and accumulated in plants and animals, especially fish that live in the oceans. So eating ocean fish is dangerous, correct? No, this is completely false, except in a handful of fish and mammals. Most fish – especially salt-water fish like tuna – may contain mercury, but health authorities insist they are safe because they also contain selenium, a non-metallic chemical element with the atomic number 34 that is vital for promoting good health.
Of the four types of sea dwellers that do have high levels of mercury and very low levels of selenium – swordfish, sharks, king mackerel and tilefish – the first two are not kosher. The US Food and Drug Administration (FDA) and our own Health Ministry have specifically warned that pregnant women especially should not eat only these four species.
In recent years, scientists have found, in fact, that the selenium in most fish binds with mercury and neutralizes the toxins, thus the more selenium in the fish you eat, the less the mercury from fish and the more healthful omega-3 fatty acids of EPA and DHA get into your body. The binding of selenium creates a new compound that makes it difficult for the body – especially brain and nerve tissue – to absorb the mercury alone.
Toxic effects of mercury include muscle weakness, numbness in the extremities, lack of coordination, damage to speech and hearing, vision problems and, in extreme cases, damage to the kidneys, brain and lungs, paralysis, insanity, coma and even death. If a large amount is consumed by pregnant women, it can cause damage to the central nervous system of fetuses in the womb. But the “magic mineral” of selenium makes eating ocean fish safer than not eating fish, despite the mercury.
Mercury, which poses such potential risk that mercury thermometers have been outlawed to prevent leaks, became notorious for “Minemata disease,” resulting from the release of methyl-mercury in industrial wastewater from the Chisso chemical factory in Japan between 1932 and 1962. Fish in the bay absorbed the toxin, and cats, dogs, pigs and people who consumed them died.
Some of the humans died in the early years, but the first proven case was a Japanese girl born in 1951 who at the age of five had convulsions and difficulty talking and walking. Others developed disorders that persisted for decades, forcing the Japanese company to compensate over 10,000 victims.
Another notorious incident involving mercury was in in the 1970s in Iraq, when a fungicide was used to treat wheat that was poisoned as a result. It was turned into bread, and people were poisoned after eating it.
DR. NICHOLAS Ralston and Dr. Laura Raymond, prominent scientists at the Energy and Environmental Research Center (EERC) at the University of North Dakota at Grand Forks, have devoted many years to the study of the mercury/selenium puzzle.
They have jointly published their research in prestigious journals such as Science, Toxicology, Ecological Health and publications of the US Environmental Protection Agency to spread the word about the beneficial interaction between selenium and mercury.
Ralston was due to deliver a lecture a few weeks ago before a nutrition conference in Tel Aviv, but due to family reasons had to cancel his appearance, and Raymond filled in for him.
Ralston has often written: “Think of dietary sele- nium as if it were your i n c o m e and dietary mercury as if it were a bill that you need to pay. Just as we all need a certain amount of money to cover living expenses such as food and rent, we all need a certain amount of selenium. And guess what foods are highest in selenium? You’re right! Sixteen of the 25 best sources of dietary selenium are ocean fish.”
Only one major study, Ralston has written, “has shown negative effects from exposure to mercury from seafood, and that seafood was pilot whale meat. Pilot whale meat is unusual in that it contains more mercury than selenium. When you eat pilot whale meat it’s like getting a bill for $400 and a check for less than $100. If that happens too much, you go bankrupt.
On the other hand, if you eat ocean fish, it is like getting a check in the mail for $500 and getting a bill for $25. The more that happens, the happier you are.”
The FDA issued an official statement in 2004 that fish such as canned light tuna, salmon and other oily ocean fish should be eaten twice a week, and even pregnant women and children can do so. But it recommended not eating shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury.
Albacore tuna, which weighs about 40 kilos each and gobble up smaller fish, have higher levels of mercury. As a result, much smaller tuna such as the “skipjack” variety – the predominant kind imported into Israel – should be preferred, as it has much more selenium and much less mercury.
Skipjacks weigh only about three-four kilos apiece. In any case, the selenium negates the presence of mercury, said Raymond, who gave an exclusive interview to The Jerusalem Post about the issue.
Ironically, the North Dakota center where the team conduct their research is almost equidistant between the Pacific and Atlantic Oceans, but it has numerous lakes and rivers with plentiful fish.
Raymond, who was born in North Dakota, earned a bachelor of science degree from the University of Arizona and a doctorate in biochemistry and molecular biology, with a focus on nutrition, at the university in her native state. She worked at the US Department of Agriculture Human Nutrition Research Center before moving to the EERC, where she focused on environmental issues and toxicology.
“Nicholas and I looked at mercury toxicity and thought it would be a short-term project, but it turned out we have been studying it for a decade,” said Raymond, who is research manager of the health and analytical research group at the EERC.
“Mercury is a unique metal in that it has ability to cross the bloodbrain barrier and the placenta. It c a n enter the brain and steal selenium in the human brain, including that of the fetus, where it especially can have devastating effects.
“At first, the studies we based our advisories involved pregnant women who had eaten pilot whale, which is a mammal and not a fish at all,” she recalled. “They had four times more mercury than selenium.
Their [the pregnant women’s] children suffered slight detriments, not devastating harm. The women ate fish rich in selenium as well, and that part of the diet was enough to offset the mercury from the whale.”
Later, Ralston and Raymond received frozen fillets of tuna, defrosted them and fed them to rodents that had been fed toxic mercury. The selenium from the tuna neutralized the harmful effects of the heavy metal.
Raymond noted that power plants in China, the manufacturing capital of the world today, burn a lot of coal, emitting a lot of mercury into the environment. Active volcanoes around the world are also a source of the toxic element. Mercury is also released from deep vents at the bottom of the ocean, in seas, lakes and rivers and in the soil. But the main source of contamination among humans is consumption of ocean fish, especially those at the top of a long food chain. Pond fish also contain mercury because they are usually fed fish meal made from ocean fish.
Everyone benefits from selenium, continued Raymond, not just pregnant women. It can be bought in capsule or pill form, but it is more beneficial to get it from natural sources, especially fish. Both taking the pill and eating significant amounts of fish will not cause harm, as the body’s tolerance for selenium is very high.
“It’s vital for body functions, and fights inflammation and cancer and is a strong antioxidant. Selenium protects against mercury toxicity, and 16 of the 25 highest dietary sources of selenium are ocean fish.”
THE STARKIST company in Israel – which obviously has a vested interest in explaining to the public that its own tuna is safe – invited Raymond here to lecture at the nutrition conference about her tuna research. Marketing executive Dganit Eshed- Priscu said that despite the name, her company, based in Tirat Hacarmel, has no connection to the famous fish-processing firm in the US, but just bought the name from the huge company.
“Tuna is a very popular food in Israel,” she said. “About 94 percent of Israeli households buy tuna regularly. It’s omnipresent as a filling for sandwiches eaten by children in school and at cafes and restaurants, as well as part of the home menu.”
When the local Internet site Ynet published in late 2012 a US article translated into Hebrew that claimed tuna was “dangerous” for pregnant women, “there was extreme panic. Some people said they stopped giving their kids tuna more than once a month. There was a dramatic reduction in our sales. Day care personnel stopped buying it. It all resulted from misinformation and exaggeration. And it’s ironic that the US FDA and Environmental Protection Agency didn’t advise at all that pregnant women not eat tuna.”
The FDA officially stated that “if a fish contains higher levels of selenium than mercury, it is safe to eat. Most species of commonly eaten fish have more selenium than mercury.The benefits of eating fish regularly far outweigh the potential risks, which are negligible.”
The panic even induced the Health Ministry’s public health department to reissue a statement that Israeli tuna was completely safe for everyone, including pregnant women – especially the small skipjack type that is sold here. Although the panic has quieted down, some misinformed gynecologists still advise women not to eat tuna or other fish during pregnancy.
“Canned albacore tuna never caught on,” recalled Eshed-Priscu. “It tasted to Israelis like chicken. They live longer than the smaller skipjack variety, so albacore has more mercury. Skipjack, with a blue silverfish skin, happens to be the kind of tuna that is richest in selenium. They also contain less mercury because they are much smaller fish. We get our tuna mostly from the waters off Thailand and the Philippines.
They are very deep ocean fish, and it takes three weeks to sail to where they are.”
Israel’s Starkist company, which is the market leader, also sells two types of canned salmon products – smoked and a spread – and a bit of herring, regular mackerel and sardines, but these also contain a lot of selenium and not much mercury. About 90% of Starkist’s sales here are of tuna.
About 80% of its tuna is sold in oil for taste and the rest in water; in the US, the proportion is the exact opposite, with the vast majority canned with water.
“We are in favor of everybody eating fish. Consuming a variety of fish is just like the need to eat vegetables of all types and colors, because they have different nutrients. Fish is definitely not a delivery system for mercury,” said the Starkist representative.
Even the Talmud recognized many centuries ago that eating fish was beneficial and recommended that it be part of the diet a few times a week.