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Curing bacon: fat on the fire.

British researchers have come up with an unexpected tiwst to the relationship between nitrates, nitrites and stomach cancer. In a study comparing people from an area where the incidence of stomach cancer is high to people in low-risk areas, they found evidence that the high-risk group had lower levels of nitrates and nitrites in their bodies. The finding, suppporting exoneration of the nitrates and nitrities found in food and water, is another chapter -- certainly not the final one -- in the increasingly intricate story of stomach cancer.

In a chemical double play, bacteria in the mouth and stomach can reduce nitrate to nitrite, a substance that can cause mutatioin in bacteria. Nitrites can react with other compounds in the laboratory to form N-nitroso compounds, including nitrosamines, which are known to cause cancer in animals.

In the lab, the progression to N-nitroso compounds is cut and dried. But what happens in the body may be a different story. While the National Research Council (NRC) recommended in 1981 that people limit their exposure to nitrates and nitrites, the matter has remained controversial (SN: 12/19 & 26/81, p. 390). Producers of cured meats such as bacon have cut down on levels of nitrites, which inhibit deadly botulism-producing bacteria. Critics contend, though, that the reduction wasn't needed because the levels weren't harmful and in any case represented only a portion of a person's total intake, since vegetables and drinking water contain nitrates and nitrites.

In the current study, David Forman, Samim Al-Dabbagh and Richard Doll of the Imperial Cancer Research Fund in Oxford looked at 414 people from parts of Wales and northeast England where stomach cancer is high, and 422 people from low-incidence areas of Oxford and southeast England. To estimate the amount of nitrates and nitrites in the body, they measured levels in the saliva.

"Contrary to what might have been expected," they report in the Feb. 21 NATURE, "it is always the high-risk population that has the lower concentrations of nitrate and nitrite." Their findings, they say, are "inconsistent with the notion that nitrate exposure is a risk factor for cancer of the stomach."

While their findings suggest positive implications for nitrates and nitrites, they concede that there may be alternative explations--some overriding, as-yet-unindentified factor. Or the salivary measurement might not accurately reflect the past or present level of nitrosamines in the stomach, or the effect might be masked by the intake of vitamin C, which inhibits the formation of N-nitroso compounds.

The last two concers are shared by Sidney S. Mirvish of the University of Nebraska Medical Center in Omaha, an adviser to the NRC panel in 1981. Because of a strong correlation between nitrate consumption and stomach cancer in 13 countries, the relationship remains an attractive theory, he says.

The subject is of considerable interest in farm areas, Mirvish says, where people are worried about increasing levels of nitrates and nitrites from fertilizer use and cattle feedlot runoff.

Peter Greenwald of the National Cancer Institute in Bethesda, Md., who was on the NRC committee, finds the study "valid, but the evidence is indirect and circumstantial.

"I think it's a good study," he says, "well done and by good people. But there's still a question there."

Epidemiological studies of people who move from high-risk to low-risk areas indicate that key factors in stomach cancer occur in childhood, years before the cancer appears, Greewald notes. People in Japan, for instance, are at unusually high risk of stomach cancer, and remain so when they move to the United States. But their U.S.-born children enjoy lower risk. The answer to the question, then, may lie in a long-term study. In the meantime, Greenwald says, the NRC recommendation to limit nitrate and nitrite intake is still a prudent one.
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Title Annotation:relationship between nitrates, nitrites and stomach cancer
Author:Silberner, Joanne
Publication:Science News
Date:Mar 2, 1985
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