A large 'ohana could be bad for your health, according to a new study that indicates a connection between family size and the risk of developing stomach cancer.

The study of more than 7,400 Japanese-American men by medical researchers at the University of Hawai'i and New York University found that those who came from families of seven or more siblings and carried certain strains of the bacterium Helicobacter pylori in their stomachs were more than twice as likely to develop stomach cancer compared with carriers who had one to three brothers and sisters.

The researchers also found the risk was greater for younger siblings in large families.

"This is a very carefully controlled study that clearly shows that there are factors in early childhood that affect the risk of developing cancer many decades later," lead researcher Dr. Martin J. Blaser said in a news release. "That early childhood events affect the risk of cancers occurring in old age is remarkable, and this may be a model for other cancers."

He speculated that one reason younger children in large families may be more vulnerable to the cancer is that they acquire the bacterium from their older siblings at a time when their immune systems are still developing. Since the bacterium has already adapted itself to a genetically related person, Blaser said, it has a "head start" in the younger child than if it were transmitted from a genetically unrelated individual.

H. pylori is a spiral-shaped bacterium associated with stomach cancer and peptic ulcers. It was isolated and identified only in the early 1990s. It can persist for decades in the mucous layer that lines the stomach. The bacterium is transmitted orally from person to person via saliva and through contact with human feces. It has been estimated that half the people in the world carry the bacterium in their stomach.

Dr. Abraham Nomura of the Cancer Institute of Hawai'i, one of the authors of the study, told The Advertiser that people who come from large families shouldn't be alarmed at the findings. However, someone with ulcers or other stomach problems who tests positive for the H. pylori bacterium should let their physician know about their family background.

"It's another clue to be attuned to the possibility of stomach cancer," Nomura said.

Large families were common in decades past when Hawai'i was largely dependent on agriculture. Nomura said families generally are much smaller now, and the rates of stomach cancer and H. pylori infection have been declining with each generation.

Stomach cancer killed 100 Hawai'i residents in 2005, according to Department of Health statistics.

The men in the study were first evaluated as part of a Kuakini Medical Center heart disease study led by Nomura, who was looking at changing disease patterns in foreign-born and Hawai'i-born residents of Japanese descent. Of the 7,429 men who were examined between 1967 and 1975, 261 developed cancer.

The cancer researchers used blood samples collected in the earlier study. Samples from the men who developed stomach cancer were tested for antibodies to H. pylori and the cagA protein strain of the bacterium. Each of those men was matched with a similarly aged subject from the original pool of men who didn't develop cancer.

The researchers then assessed whether the risk of stomach cancer was associated with the number of siblings a man had and whether he was older or younger than his brothers and sisters, according to the news release. They found that men who had cancer were more likely to carry H. pylori compared to age-matched men who didn't carry it, and that those with cancer had a large number of siblings.

They also found that in men who had the cagA strain of H. pylori, those from the largest families had the highest risk of stomach cancer, the release said.

Blaser said it's possible the findings could be affected by other factors such as other childhood infections or stress associated with large families, but based on genetic studies of H. pylori, he believes "the genetic adaptability of H. pylori explains how this bacterium can 'pre-adapt' to a genetically related individual, setting the stage for the development of cancer 50 to 70 years later."

Other study authors are Guillermo Perez-Perez from NYU, and James Lee and Grant Stemmerman from the University of Hawai'i. The study was supported by grants from the National Institutes of Health and by the Ellison Medical Foundation Senior Scholar in Infectious Diseases Award.

Reach Christie Wilson at cwilson@honoluluadvertiser.com.