Fertility and Smoking: Mortality Due to Endometrial Cancer in Japan

Abstract

Background: In Japan, the crude mortality rate (mortality rate) due to endometrial cancer is increasing. Using published data, the contributions of fertility and smoking, which are risk factors for endometrial cancer, were analyzed from the viewpoint of age and time.

Materials and Methods: The data on the numbers of deaths due to endometrial cancer (ICD10 code, C54; from 1995 to 2019), live births, and female population were obtained from the website of Ministry of Health, Labour and Welfare of the Japanese Government (the vital statistics of Japan). The data on the smoking rates of females were obtained from the website of JT (Japan Tobacco). Pearson’s correlation coefficients were calculated.

Results: There was a large difference in the mortality rates of endometrial cancer between the groups aged 49 years or younger and the groups aged 50 years or older. There were strong negative correlations between the birth rate in the group aged 20-29 years and the mortality rates in the groups aged 40-49 (r=-0.901) and 50-59 years (r=-0.794). However, there was no correlation between the birth rate in the group aged 20-29 years and the mortality rate in the group aged 60-69 years (r=0.00). There was a strong positive correlation between the birth rate in the group aged 30-39 years and the mortality rate in the group aged 50-59 years, which seems to reflect the delay in childbirth from the 20s to the 30s. There were positive correlations between the smoking rate in the group aged 20-29 and the mortality rates in the groups aged 40-49, 50-59 and 60-69 years (r= 0.882, 0.818, 0.896, respectively). In contrast, there were negative correlations between the smoking rate in the group aged 50-59 years and the mortality rates in the groups aged 70-79 (r=-0.702) and 80-89 years (r=-0.937).

Conclusions: The preventive effects of giving birth in the 20s may be much larger than those of giving birth in the 30s. The contributions of smoking might vary, depending on the age at onset of this cancer and/or the duration of smoking. It is thus necessary to reexamine the contributions of the risk factors more minutely from the viewpoint of age and the period of exposure.