People who have been infected with the ulcer-causing bacteria Helicobacter pylori are more than twice as likely to develop diabetes later on as people who do not have signs of the infection, according to a new study of Latino adults in California.
The results don't prove that the bug causes diabetes, but "it is strongly related to predicting type 2 diabetes," said Allison Aiello, the senior researcher on the study and a professor at the University of Michigan in Ann Arbor.
Earlier studies looking at the relationship between H. pylori infection and diabetes have had inconsistent results -- some have shown a link, while others have not.
Aiello and her colleagues point out in their report in the journal Diabetes Care that previous research has only been snapshots in time of who had diabetes, who had the infection and who didn't.
To try to get a better fix on whether one condition might cause the other, the group tracked nearly 800 people for a decade.
None of them had type 2 diabetes, the kind related to being overweight, at the beginning of the study.
But over time, 144 people developed the disease, and 97 percent of those had tested positive for H. pylori at the start of the study.
By contrast, 91 percent of the people who didn't develop diabetes had tested positive for H. pylori.
After the researchers took into account factors such as vascular disease, smoking and being overweight, they found that the risk of developing diabetes was 2.7 times higher among the group of people who had the infection.
According to the Centers for Disease Control and Prevention, about two-thirds of people worldwide have been infected with H. pylori, but most never experience any symptoms.
About eight percent of the United States population has diabetes.
Because the researchers were able to follow people over time and show that the diabetes cases developed after people were infected with H. pylori gives "more credence to a potential causal relationship," they wrote.
Dr. Alain Bertoni, a professor at Wake Forest Baptist Medical Center who was not involved in the study, agreed that "the results are suggestive that this is a causal relationship," but offered other possibilities that could explain the findings.
"It is possible that some factor not measured (a confounder) that is associated with NOT being H. pylori positive...is actually a protective factor, rather than H. pylori is causing diabetes," Bertoni wrote in an email to Reuters Health. "For example, the authors did not consider physical activity."
He also said that perhaps people with the bacterial infection go to the doctor more often for stomach troubles, giving them a better chance of having their diabetes detected.
The researchers did find that if they accounted for people who were taking antacids or antibiotics to treat the infection it did not alter their results.
They also did not see a similar link between other infections -- namely, herpes, varicella virus, cytomegalovirus, and the bacterium Toxoplasma gondii -- and diabetes.
It's not clear why H. pylori and diabetes are related, though Aiello said there is speculation that the bacteria could alter the conditions in the gut or promote inflammation that might contribute to diabetes.
She and her colleagues found an extremely high rate of infection among the people in her study, with more than 90 percent testing positive.
"It's pretty amazing, especially given that we have treatments for H. pylori," Aiello said.
It will be important for future studies to show if H. pylori does indeed have an influence on diabetes, said Aiello, because the infection can be taken care of.