BACKGROUND - Gastric cancer incidence rates are consistently lower in women than men in both high and low-risk regions worldwide. Sex hormones, such as progesterone and estrogen, may protect women against gastric cancer.
OBJECTIVE - To investigate the association of menstrual and reproductive factors and gastric cancer risk.
METHODS - These associations were prospectively investigated in 73 442 Shanghai women. After 419 260 person-years of follow-up, 154 women were diagnosed with gastric cancer. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated using Cox proportional hazards models adjusted for age, body mass index, education, income, and cigarette use.
RESULTS - No associations were observed between gastric cancer risk and age of menarche, number of children, breast feeding, or oral contraceptive use. In contrast, associations were observed with age of menopause (HR 0.80 per five-year increase in menopausal age, 95% CI 0.66-0.97), years of fertility (participants with less than 30 years of fertility were at increased risk compared with those with 30-36 years of fertility, HR 1.90, 95% CI 1.25-2.90), years since menopause (HR 1.26 per five years, 95% CI 1.03-1.53), and intrauterine device use (HR for users 1.61, 95% CI 1.08-2.39).
CONCLUSIONS - These results support the hypothesis that female hormones play a protective role in gastric cancer risk.