Reproductive and hormonal factors in male and female colon cancer.

We analysed data from a case-control study in the Netherlands in order to investigate whether reproductive events and hormonal factors are similarly related to colon cancer risk in men and women after adjustment for dietary factors. In total, 232 colon cancer cases (102 women, 130 men) and 259 controls (123 women, 136 men) were interviewed about life style, medical conditions and usual dietary patterns, using a structured dietary history technique. In women, age at first childbirth was positively associated with colon cancer risk (odds ratio (OR) age > or = 26 vs < 26 years, 1.7; 95% confidence interval (CI), 0.9-3.3). Women with three or more children were at reduced risk compared with women with one or two children (OR, 0.6; 95% CI, 0.3-1.1). When women had had their first child after the age of 26 years, parity was observed to be important (for one or two children vs > or = three children: OR, 2.8; 95% CI, 1.1-7.0). For men, opposite but non-significant associations were found. Adjustment for dietary patterns and other risk factors did not change the estimates markedly. Of the hormonal factors, late age at menarche decreased risk (OR, 0.5; 95% CI, 0.3-0.9) while late age at natural menopause slightly increased risk. Our study provides additional support for the role of reproductive status in the aetiology of colon cancer in women, independently of dietary factors.