In a letter to the BMJ, Dr Scott Montgomery writes that this reflects improvement in hygienic conditions with time, which, once reaching a threshold, become a risk for Crohn's disease.
Strong inverse relation between mortality from gastric cancer and incidence of Crohn's disease.
This may be due to a changing exposure pattern to infectious agents in early life - particularly at an older age and lower dose.
In contrast, infection with Helicobacter pylori has been inversely correlated with inflammatory bowel disease in some studies. It is a marker for overcrowding, large families, and high birth order as well as being a gastric carcinogen.
When Drs. Montgomery and Morris correlated mortality from gastric cancer with the incidence of Crohn's disease, a strong inverse relation was found. This is apparent for both sexes and across 26 countries. The association was not seen when mortality from cervical, prostate, or lung cancer was compared with incidence of Crohn's disease, and it was also not present for ulcerative colitis.
One possible source of confounding is that falling mortality from gastric cancer will indicate improvements in socioeconomic and healthcare factors related to survival, rather than simply incidence of gastric cancer.
Where comparable figures were available, however, incidence of gastric cancer did correlate well with mortality.
Dr Montgomery concluded that, "Despite the limitations of ecological studies, we believe that this study adds support for the role of contrasting early environmental influences in the aetiology of both Crohn's disease and gastric carcinoma.
"Patterns of early infection and colonisation are likely to be important in the aetiology of both diseases."