Salt and vitriol


By Michael Day AN ARTICLE in a leading science journal has ignited a heated debate about whether eating large amounts of salt leads to high blood pressure. The journal has come under fire for failing to state prominently that the author of the article, which questions the idea that salt causes hypertension, has links with the food industry. Many researchers believe that a high salt intake can cause high blood pressure, which in turn can lead to strokes and coronary heart disease. But in a signed editorial in last week’s Science (vol 281, p 933), David McCarron of Oregon Health Sciences University in Portland disputes that link. McCarron believes the idea is a fad that has been hyped by nannying public health officials. “This is a superb example that started in the 1970s of public policy being ahead of the scientific facts,” he told New Scientist. He says blaming salt is harmful, as it deflects attention from deficiencies in our diets, such as lack of fruit and vegetables, that are “far more likely to contribute to the prevalence of hypertension than salt”. The article has prompted an angry response. “It’s full of distortions,” says Graham McGregor, a specialist in blood pressure at St George’s Hospital Medical School in London. He says the article fails to acknowledge controlled studies in Portugal and Holland which show that reduced salt intake can significantly lower blood pressure. And the article unfairly dismisses results from chimpanzee studies as irrelevant, according to McGregor. The US Center for Science in the Public Interest has attacked Science for failing to make McCarron’s links to the food industry clear. “The public should know McCarron’s work is part of an effort by the food and salt industries to discredit the evidence linking salt and hypertension,” says Bonnie Liebman, the centre’s nutrition director. “It is unfortunate that Science chose not to fully reveal his industry connections.” McCarron is a consultant to the Salt Institute, a salt traders’ organisation based in Virginia, from which he receives $3000 a year. The affiliation is mentioned in Science—but not in McCarron’s editorial. It appears only halfway through an accompanying news focus which is nine pages long. “It’s so long and boring I doubt anyone other than those with a special interest in the subject would read it,” says McGregor. Neither article mentions that McCarron receives grants from the US National Dairy Council. However, a spokeswoman for Sciencesays: “We’re happy about the validity and integrity of both articles.” McGregor says it is in the interests of food manufacturers to downplay the link between salt and high blood pressure because so many foods contain large amounts of salt for flavouring. “Drinks manufacturers have an interest too, because salt is the most important factor in causing thirst,” he adds. McCarron counters that it’s not who pays for the research that matters, but whether the results of studies can be verified. He says his opponents failed to take into account recent reviews of the data, such as a study reported last year in Archives of Internal Medicine (vol 157, p 1117) which found no evidence that salt causes hypertension. Other researchers, including Theodore Kotchen of the Medical College of Wisconsin, agree that diets rich in potassium, calcium, magnesium and fresh fruit, and low in fat, could help fight hypertension. But he believes excess salt is also a major factor. In Britain, a meeting of experts in December hosted by the British Heart Foundation is sending its recommendations to the government’s Chief Medical Officer,
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