www.newscientist.com/news/news.jsp?id=ns99995002
com news service The steep rise in some cancers of the gullet in developed countries could be explained by the massive increase in the consumption of fizzy soft drinks, suggests a new study. The volume of carbonated soft drinks downed in the US has increased nearly five-fold in the 50 years, while in the last 25 years rates of esophageal adenocarcinoma have rocketed by nearly six-fold in white males, the group with the highest soft drink consumption. Mohandas Mallath, head of the digestive diseases department at Tata Memorial Hospital, India, and colleagues found a "very significant correlation" between the rise in consumption and esophageal cancer globally. The effects took about 20 years to come through, they believe. The trend was seen in other countries where fizzy drinks have risen in popularity, such as the UK and Australia. But in countries where soft drinks have not caught on like Japan or China, there has been no increase in the cancers affecting the esophagus, the tube linking the mouth and stomach. "The surprisingly strong correlation demonstrates the impact of diet patterns on health trends," says Mallath. "As the rates may continue to rise for another 20 years, we believe that more epidemiological studies are urgently required to establish the true association." Plausible explanation But both Mallath and nutrition expert, Lee Kaplan at Massachusetts General Hospital, say that the association cannot be taken as a causal link at this stage. "This is only a correlation and doesn't in any way indicate causality," Kaplan told New Scientist. "There are a whole variety of things that occur in modern society. Refrigerators are associated with cancer - but they don't cause it." However, previous studies suggest there is a plausible biological explanation to link soft drink consumption with esophageal adenocarcinoma. Mallath says that fizzy drinks can lead to gastric reflux which causes the gullet to become acidic for long periods. Gastric reflux is the most important risk factor for esophageal adenocarcinoma, he says. "If you drink a quarter of a litre of water, your stomach distends by a quarter of a litre," he explains. "But if it's a carbonated drink, your stomach may distend to maybe half a litre. This causes reflux - the acid of the stomach is thrown back into the food pipe." Lowered pH A Canadian study previously showed that drinking 350 millilitres, or just one can of soda, a day lowers the pH of the esophagus to less than four for 53 minutes. This would not cause a problem in itself, Mallath told New Scientist, but two cans a day over 40 years might.
Digestive Disease Week Kaplan notes that soft drink consumption might be a "marker" for a lifestyle or dietary choices that increase the risk of esophageal adenocarcinoma. For example, heavy consumption of fizzy drinks could lead to obesity, which is itself associated with reflux disease. He also notes that some people with reflux develop Barrett's esophagus, which is a precursor to esophageal cancer, particularly adenocarcinoma. In contrast, the levels of squamous esophageal cancer have remained steady over the years. Mallath and team analysed data from the US department of agriculture which showed that per capita consumption of fizzy drinks rose by more than 450 per cent, from 108 gallons in 1946 to 422 gallons in 2000. Esophageal adenocarcinoma rates rose by more than 570 per cent from 1974 to 2000 in white American males. The results were presented at the Digestive Disease Week conference in New Orleans, US, on Monday.
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