Being a member of a large family may not be best for your health. A new study found that family size greatly influenced the development of stomach cancer linked to the bacterium Helicobacter pylori, and younger siblings from large families appeared to be especially vulnerable to the most common type of stomach cancer.
These latest findings are based on the records of more than 7,000 Japanese-American men who were followed over a 28-year period. The researchers found that those men who carried certain strains of the bacterium in their stomachs and came from families of seven or more siblings were more than twice as likely to develop stomach cancer compared to carriers who had one to three brothers and sisters.
The findings are reported January 16, 2007, in the online issue of Public Library of Science (PLOS) Medicine.
“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,” says Martin J. Blaser, M.D., Frederick King Professor and Chair of the Department of Medicine, and Professor of Microbiology, who led the study. “That early childhood events affect the risk of cancers occurring in old age is remarkable, and this may be a model for other cancers.”
Dr. Blaser speculates that younger children in large families 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, namely the older sibling, it has a “head start” in the younger child, whose immune system is less well defended. This sets the stage for a more virulent, better adapted bacterial population than would occur otherwise if the bacterium was transmitted from a genetically unrelated individual.
H. pylori, a spiral-shaped bacterium that lives in the mucous layer lining the stomach where it can persist for decades, is associated with stomach cancer and peptic ulcers. It is transmitted orally from person to person, such as by sharing saliva, and through contact with human feces. It has been estimated that half the people in the world carry the bacterium in their stomach.