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Fish linked to heart attack risk ~ mercury could undermine health benefits, study says
James Meikle, health correspondent
Thursday November 28, 2002
The Guardian
Eating fish with high mercury levels might increase consumers' risk of suffering a heart attack, the very health threat fatty acids in fish oils are meant to counter, scientists said last night.
They also suggested that food safety advice that women of child-bearing age and under-16s should not eat swordfish or shark might have to be extended to everyone.
Authors of an international study covering eight European countries and Israel insist people should carry on eating other fish or fish oil supplements less contaminated with mercury to protect their hearts.
But the latest research, published in the New England Journal of Medicine, adds to the bewildering mixed messages that are now being given over the safety of fish. It warned that the mercury levels in some fish were so high it counteracted benefits to the heart from fatty acids.
The government's food standards agency said the evidence would be added to that being studied by advisers on toxicity who are reviewing health messages. For the moment, it would not change its advice that swordfish, shark and marlin could be eaten by adults deemed not at risk as long as it was only once a week.
It has stressed up to now that the benefits of a fish diet outweigh the risks and that not enough Britons eat fish anyway. It says they should each week be consuming one portion of oily fish, such as mackerel, sardines, salmon or trout, and one portion of white fish, such as cod, haddock or plaice, good sources of protein and an alternative to meat.
Some nutritionists believe this is insufficient and the advice should be to eat more fish while other advisers have already warned this would increase the levels of potentially cancer-causing dioxins and other contaminants beyond safety limits. Fish are major carriers of the contaminants.
Advice for women and children not to eat swordfish, shark and marlin was issued in May and followed similar warnings from the US food and drug administration. But that was because of the danger that methylmercury, absorbed mostly by predator fish high up the food chain, might lead to development problems in foetuses, infants and children.
The heart risk emerged as researchers at the Johns Hopkins Bloomberg school of public health, Baltimore, and across nine countries, compared nail clippings, where mercury acts as a biomarker for long-term exposure, from 684 men who had recently had a heart attack and 725 men who had not. They also compared adipose tissues to gauge their exposure to fish oils. They found mercury levels in men who had had a heart attack were 15% higher than in healthy controls.
Previously only fish from areas heavily contaminated with mercury had been considered to give a risk of causing heart attacks. But now it seems far lower levels of mercury concentration can create a risk.
Elisio Guallar, of the research team, said: "Although it is believed that fish intake may reduce the risk of cardiovascular diseases, epidemiological studies of fish intake or fish oil levels and coronary heart disease are contradictory. Our findings suggest that mercury found in fish may counteract the benefits of the omega three fatty acids, also present in fish.
"Exposure to methylmercury is a concern in specific high-risk groups, such as pregnant women and women of childbearing age who may become pregnant, but this warning perhaps should be extended to the general population."
The British part of the study was conducted in Edinburgh, and the British Heart Foundation, which financed it, said last night: "It would be interesting to see the results of wider research in the UK to understand the levels of mercury in fish and assess the environmental and health implications." It said people should still try to eat two portions of fish a week, one oily.
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