Family size is a risk factor for stomach cancer

Reported by Susan Aldridge, PhD, medical journalist

People from larger families are more vulnerable to stomach cancer because of helicobacter pylori infection.
The bacterium Helicobacter pylori has been linked to stomach cancer. The bug actually lives in the stomach and it's thought that half the people in the world are infected with it - although in most cases it is harmless. Researchers at New York University Medical Center now report that Helicobacter can make family size an issue in stomach cancer.

They report on a group of 7,000 Japanese-American men who have been followed for a 28 year period and have been tested for the presence of Helicobacter in childhood blood samples. Those infected with certain strains were more at risk if they came from a large family than if they came from a small one. Specifically, those who were younger siblings in a family with seven or more kids had twice the chance of developing stomach cancer compared to those who had one to three brothers and sisters.

The researchers believe that Helicobacter first adapts itself to an older sibling and then invades the younger one at a time when their immune system is still developing. This sets the scene for cancer many years later. It may be that this model could help us understand how other forms of cancer develop in later life after exposure to various childhood factors.

Source
Public Library of Science (PLOS) Medicine 16th January 2007

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