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Intuitively, scientists have long believed that soft drinks -- an addictive mix of carbonated water, sugar (or artificial sweeteners), flavourings and salt -- were bad for the digestive system.

Research published in 2004 seemed to confirm their worst fears, suggesting that the steady rise in soft-drink consumption was to blame for the soaring number of cases of cancer of the esophagus -- one of the most deadly forms of the disease.

But now a new study is casting doubt on the pop-cancer link, suggesting that, in fact, regular consumers of soft drinks are less likely to develop cancer of the esophagus.

"The theory that soft drinks could be causing this cancer was picked up by the media and widely disseminated," said Susan Mayne, a professor of epidemiology and public health at Yale School of Medicine in New Haven, Conn.

"However, there was no direct evidence to bear on this hypothesis, until we initiated our analysis," the researcher said.

The new study, published in today's edition of the Journal of the National Cancer Institute, involved 1,095 patients suffering from esophageal cancer and a control group of another 687 people without cancer.

Dr. Mayne and her team found that about 80 per cent of study participants were regular consumers of carbonated soft drinks.

But those without cancer actually drank more pop -- and diet soft drinks in particular.

While this might suggest that carbonated drinks actually reduce the risk of cancer of the esophagus, Dr. Mayne cautioned against that conclusion.

Rather, she said, people who choose diet drinks are likely to be more health conscious, and not have other risk factors for esophageal cancer.

Cancer of the esophagus is believed to be almost entirely preventable.

Established risk factors include smoking, obesity, a history of gastroesophageal reflux, frequent heartburn, and low fruit and vegetable consumption.

There is no evidence, Dr. Mayne said, that "avoidance of carbonated soft drinks would be an effective strategy to lower risk" for cancer.

She noted that the earlier much-publicized study, conducted by researchers at Tata Memorial Hospital in India, did not involve cancer patients.

Rather, its conclusions were based on the almost identical increase of 350 per cent in per capita consumption of soft drinks and the incidence of esophageal cancer since the mid-1970s.

Mohandas Mallath and his team said the link seemed biologically plausible. He said carbonated drinks cause the stomach to distend, which can provoke gastric reflux, a risk factor for esophageal cancer.

It was theorized that stomach acids would irritate the lining of the esophagus, and thereby set the stage for cancer.

While fizzy drinks seemed to be a culprit, the association now appears to be coincidental.

An estimated 1,600 Canadians will die of esophageal cancer this year and another 1,450 will be newly diagnosed, according to the Canadian Cancer Society.

Per capita annual consumption of carbonated soft drinks was 110 litres in 2004, according to Refreshments Canada, an industry group.

Many health woes have been blamed on rising consumption of pop, particularly among young people, including the rise in childhood obesity, high blood pressure, dental caries and gastric cancers.

But, in Canada, soft-drink consumption has actually been falling for a number of years, replaced by sports drinks, energy drinks, juices and bottled water.