Family Size and Stomach Cancer

Family size influences the development of stomach cancer linked to the bacteria Helicobacter pylori, with younger siblings most vulnerable, says a U.S. study.

The findings are based on the records of more than 7,000 Japanese-American men who were followed over a 28-year period.

Researchers at the New York University Medical Center found that 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.

That early childhood events affect the risk of cancers occurring in old age is remarkable, and this may be a model for other cancers, said Dr. Martin J. Blaser.

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.

The findings are reported in the online issue of PLoS Medicine.