By Janet Raloff

Web edition: January 12, 2006

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POP ANALYSIS. Although soft drinks are acidic, they don't appear to contribute to disease in the esophagus.

Credit: iStockphoto

Soft drinks may not constitute a health food, but according to a new study, neither are they the carcinogenic villains that recent media accounts suggested.

In 2004, researchers from Tata Memorial Hospital in Bombay, India, reported that rising esophageal cancer incidence in the United States over the past quarter-century correlates with a rise in soft-drink consumption starting 50 years ago. After the researchers spoke at a major meeting on digestive diseases in May of that year, news reports spread awareness of the putative soda pop–cancer link.

Although not a particularly common disease, cancer of the muscular tube connecting the throat and stomach yields a 5-year survival rate of only 14 percent. In 2004, more than 13,000 people in the United States died from esophageal cancer.

Shortly after the 2004 meeting, Susan T. Mayne, a nutritional epidemiologist at Yale University, heard a television broadcast mentioning the Indian report. "I quickly went online and pulled up an abstract of the presentation," she says. The authors offered only circumstantial data linking the disease to carbonated beverages. However, they argued, because a cause-and-effect relationship was biologically plausible, somebody ought to probe it further.

"I realized," Mayne recalls, "that I was sitting on a data set with the [requested] information." It was the largest U.S. epidemiologic study for this particular disease, containing information collected from roughly 1,100 esophageal cancer patients and another 700 cancerfree people in Connecticut, New Jersey, and Washington State. Among questions asked of each volunteer had been his or her typical intake of soft drinks.

In the Jan. 4 Journal of the National Cancer Institute, Mayne's group reports finding zero support for the idea that drinking soda pop might foster esophageal malignancies. In fact, heavy consumers of diet sodas faced only half the risk of developing this cancer as did people who avoided such beverages.

Acid reflux, the release of stomach acid back into the esophagus, is a major risk factor for cancer in this tissue. Many people with reflux disease have found that soft drinks exacerbate their symptoms and so avoid these beverages, Mayne notes. To account for the possibility that reflux sufferers limiting their consumption of these beverages might have biased the findings, her team went back and eliminated data from any individual who had reported reflux symptoms. When the researchers ran their analysis again, heavy soft-drink consumers still showed no increased risk of esophageal cancer.

In earlier work, "we've identified many other risk factors that probably do account for the [esophageal cancer] epidemic," Mayne told Science News Online. The two biggest contributors appear to be reflux disease and obesity. Smoking emerged as a modest risk factor, and diets rich in fruits and vegetables appeared to protect people from this cancer.

Her team's new study "is the first direct test of the hypothesis that soft drinks might contribute to esophageal cancer," says Mayne. The data, she says, "now indicate the exact opposite."