Abstract
BACKGROUND: Dysmenorrhea is chronic and cyclic pain during menstruation and is a common gynecological problem worldwide. Although there are several reported risk factors for dysmenorrhea, the findings of previous studies are inconsistent. This study aimed to identify lifestyle factors associated with dysmenorrhea. METHODS: The study population comprised 36,665 premenopausal female nurses aged 20-49 years who completed the Japan Nurses' Health Study (JNHS) baseline survey. Out of grades 0-4 of menstrual pain, dysmenorrhea was defined as grades 2-4. Multivariable modified Poisson regression analysis was used to examine the associations between dysmenorrhea and possible risk factors, namely age, current menstrual cycle, marital status, parity, current body mass index (BMI), smoking status, alcohol consumption, work shift, physical activity, sleep duration, and soybean isoflavone intake. RESULTS: There was a significant negative association between age and the prevalence ratio (PR) of dysmenorrhea (p < 0.0001). Older age and parity were significantly associated with decreased multivariable-adjusted PRs. The factors significantly associated with increased PRs were an irregular menstrual cycle, being underweight (BMI < 18.5 kg/m(2)), smoking, consuming alcohol, short sleep duration, and night shift work. Although the age-adjusted PRs of total isoflavone aglycone equivalents, tofu intake, and miso soup intake showed a significant linear trend toward decreased PRs, there was a significant decrease in multivariable-adjusted PRs only in the "almost every day" tofu-intake group. CONCLUSION: The JNHS baseline survey revealed that the factors associated with dysmenorrhea in Japanese women were age, parity, menstrual cycle, being underweight, and lifestyle factors, including soybean food intake.