Diet versions showed no link, but having one sugary drink a day carried 2.5 times the stomach cancer risk in a study of 112,284 adults.
Cutting back on soda is usually about weight or teeth. Researchers have previously linked sugary drinks to cancer of the colon and rectum, the breast and the liver, but the stomach has stayed an open question.
Now a study of American health workers links it there too.
Adults who drank at least one sugary beverage a day were more than twice as likely to develop stomach cancer as adults who almost never did. Worldwide, stomach cancer is the fourth leading cause of cancer death.
Andrew T. Chan, a gastroenterologist and epidemiologist at the Mass General Brigham Cancer Institute, was the senior author. Participants chose their own drinks, so the study shows an association rather than a cause.
“This is the first study to demonstrate an association between sugar-sweetened beverage intake and gastric cancer in a U.S. population,” Chan said. He added that researchers have “known very little about how diet might contribute to this cancer.”
Few habits are this widespread. Mass General Brigham puts the share of U.S. adults who report drinking one or more sugar-sweetened beverages every day at about 65 percent.
The researchers drew on two long-running projects. The Nurses’ Health Study enrolled female nurses in 1976, and the Health Professionals Follow-Up Study, run out of the Harvard T.H. Chan School of Public Health, signed up male health professionals a decade later.
Every four years, participants filled out a long food questionnaire that asked how often they drank soda, punch, lemonade and sports drinks. One serving meant 8 ounces (240 ml).
Altogether 112,284 people were tracked. Across 3.2 million person-years of follow-up, 278 of them developed stomach cancer.
Only the heaviest drinkers of sugar-sweetened beverages stood out. People having one to three servings a month, one to three a week, even four to seven a week all looked much like the people who almost never drank them.
Daily drinkers were the exception, however,, at 2.45 times the risk. This is the habit that is already tied to type 2 diabetes and heart disease.
The same questionnaires also asked about low-calorie carbonated drinks. People who drank those had no higher rate of stomach cancer, at any level of intake.
That stayed true after the team adjusted for weight, smoking, alcohol, exercise, diabetes and overall diet quality.
Artificial sweeteners are not free of suspicion themselves. The International Agency for Research on Cancer lists aspartame, one of the most common of them, as a possible cause of cancer in people. For the stomach, this study turned up nothing.
Looked at separately, women and men both showed the pattern at different strengths. Among the nurses, women drinking more than one sugary beverage a day were about three times as likely to develop stomach cancer as women who almost never did.
Among the men, the risk was closer to twice, and weak enough that chance couldn’t be ruled out.
Both of those figures rest on very few people. Thirteen women and 18 men in the heaviest-drinking groups developed stomach cancer over the entire study. That’s why the men’s estimate is shaky and the women’s is not, and it’s the main thing a larger study would fix.
Fructose is the main sweetener in these drinks, so the team also sorted everyone by how much of it they took in from all sources. Again the heaviest consumers had more stomach cancer, in the whole group and among the women.
The best-known cause of stomach cancer isn’t food at all. Helicobacter pylori settles into the stomach lining and can keep it inflamed for years, and the National Cancer Institute lists long-running infection as a major cancer risk factor.
Other research points at mouth bacteria that may feed the same disease, and one team is trying to fight the bacterium with chocolate.
Blood from 940 participants had already been tested for antibodies to that microbe during an earlier colorectal cancer project. Infection turned up in 36.7% of those tested among the nurses and 34.0% among the men.
People who drank more sugary beverages were no more likely to be infected than anyone else. So the drinks aren’t clearing a path for the bacteria.
This is observational research, which means the researchers watched what people chose to drink rather than assigning it. Heavy soda drinkers differ from non-drinkers in ways that a questionnaire can’t fully capture. It is possible that other factors also affected cancer risk.
The authors also name what they couldn’t check. They had limited information on who carried the stomach germ and on where each tumor grew. Family histories were thin too, as were records of who had ever had a camera passed into their stomach.
Everyone in both studies joined between the ages of 30 and 75, and most of them were White. The researchers couldn’t examine other racial and ethnic groups, or adults who take up the habit young. Sugary drinks have also been tied to depression in women.
Researchers still can’t say how a sweet drink would damage a stomach. The authors list six ideas carried over from work on other cancers: weight gain, insulin resistance, hormone imbalance, inflammation, DNA damage, and a disturbed balance of microbes.
None of these has been tested against this cancer.
Repeating the study in groups that these nurses and health professionals don’t represent is the next job. Until someone does, 278 cancers in one cohort of American health workers represent the entirety of the evidence.
The full study was published in the journal Gastro Hep Advances.
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