In our study, the life expectancy at birth was 79.43 years in urban areas and 73.90 years in rural areas, implying that data from urban areas and rural areas can be used for determining sensitivity to urbanization. Urbanization is associated with elongated life expectancy and thus higher rate of diseases that occur in elderly group; that aging and urbanization were included in one model as covariates could be eliminated the influence of elongated life expectancy for analyzing effects of urbanization on diseases.
Nutritional deficiencies could be referred to as an undeveloped rural disease. In present study, the mortality due to nutritional deficiencies was higher in rural areas than that in urban areas, implying that data sets were reliable. Although the diagnostic technique could be improved with urbanization, the rates of objective diagnosis (as evidenced by laboratory, pathologic, imaging and/or surgical intervention findings) were almost same in two regions, suggesting that bias from the improved diagnostic technique could be limited.
The B value was used to quantify the contribution of changes in urbanization to mortality from gastrointestinal disease revealed that these contributions varied. A higher B indicated greater risk of disease with urbanization (negative value implied a protective effect). We defined gastrointestinal diseases with a value of B (region) greater than zero as the “developed urbanized disease”, and from our analysis, four gastrointestinal diseases (diabetes, colon/rectum cancer, hepatitis C and pancreas cancer) were developed urbanized disease. Urbanization may be a protective factor for other gastrointestinal diseases.
It is well known that the incidence of diabetes mellitus increases greatly with the development of a society [16,17,18]. Therefore, diabetes mellitus could be referred to as a developed urbanized disease. In the present study, diabetes mellitus was included in a group of developed urbanized disease, implying that statistical method was appropriate in our study.
As aging is a key observed variable for non-communicable diseases  and an uncontrollable factor in mortality, it is important to evaluate the effects of aging on gastrointestinal disease with urbanization. The B value of interaction between age and region (cities and rural areas) could be considered as indicator to assess role of age in mortality from gastrointestinal disease with urbanization, where a larger B value implied a stronger effect of aging with urbanization; the negative B value implied a stronger effect of other urbanized factors except aging in death with urbanization. We found that the value of B (interaction between region and age) for the 12 gastrointestinal diseases also varied.
We defined gastrointestinal diseases with a value of B (interaction between region and age) greater than zero as the “old diseases”, and from our analysis, nine gastrointestinal diseases (stomach cancer, ulcer, liver cancer, colon/rectum cancer, pancreas cancer, diabetes, hepatitis C, appendicitis and diarrhea) were old diseases; for these diseases, aging could become a major cause of death with urbanization. This indicates that common protective interventions for health or aging process have an important role.
The scatter diagram represented the effects of aging and urbanization on gastrointestinal disease together as the dividing value. We divided the 12 gastrointestinal diseases into three groups according to their location on the diagram; each group represented gastrointestinal diseases with different attributes.
The group in the lower left quadrant, was termed other factor and undeveloped rural disease and includes esophageal cancer, liver cirrhosis and hepatitis B. Urbanization may be a protective factor for this group of diseases. We also clearly saw a tendency toward other factor (non-aging factors) with the development of society and the increase in the life expectancy, suggesting a independent of aging and a characteristic of programmed onset (occurrence of disease in a certain life stage) . Accordingly, an emphasis on increasing basal health status may contribute to disease preventative strategies in this group.
The group in the lower right quadrant represents disease associated with the old population and undeveloped rural areas and includes stomach cancer, liver cancer, gastrointestinal ulcers, diarrhea and appendicitis. Urbanization may also be a protective factor for this group of diseases. Undeveloped rural risk factors for this disease group appear to be eliminated with urbanization. Therefore, aging will be a major causes of death with urbanization for this group of diseases. Accordingly, an emphasis on public health may contribute to disease preventative strategies in this group.
The group in the upper right quadrant shows disease associated with the relative-old onset and developed urbanized disease and included pancreas cancer, colon/rectum cancer, hepatitis C, and diabetes. That disease occurs relative-old implies the increase of age at disease onset is so many as the increase of life expectancy. The aging and increase of life expectancy may be major causes for mortality, suggesting this group of diseases should be prevented by delaying aging, although it may be difficult.
The group in the upper left quadrant shows disease associated with the other factor and developed urbanized disease; unexpectedly, there is not major gastrointestinal diseases in this group. This group disease implies the increase of age at death is not so many as the increase of life expectancy. The other risk factors (non-aging factors) from urbanization, such as sedentary lifestyle and higher-kilojoule food intake [21,22,23], may be major causes for mortality, suggesting this group of diseases could be prevented by avoiding these urbanization associated risk factors. Further study is needed to explore whether these risk factors from urbanization have important role in occurrence of some gastrointestinal diseases or not.