Association between underweight and menstrual pain severity, irregular menstruation in a young Japanese population

Dysmenorrhea is closely linked to quality of life in females. Abnormal body mass index (BMI), including underweight and obesity, increases the risk of developing chronic diseases. However, the association between abnormal BMI and dysmenorrhea remains inconsistent. In this study, 4,999 female students were enrolled. Information on lifestyle and menstrual status (pain severity, irregularity, and medication) was collected through self-reported questionnaires. Underweight and overweight were defined as BMI < 18.5 and BMI ≥ 25, respectively. The prevalences of underweight, overweight, severe pain, and irregular menstruation were 17.1%, 6.8%, 15.2%, and 13.9%, respectively. Underweight was significantly positively associated with severe menstrual pain (adjusted OR: 1.28, 95% CI: 1.05–1.56; p for trend = 0.047), medication for menstrual pain (adjusted OR: 1.39, 95% CI: 1.13–1.70; p for trend = 0.006), and irregular menstruation (adjusted odds ratio [OR]: 1.32, 95% confidence interval [CI]: 1.08–1.61; p for trend = 0.04). However, no association between being overweight and dysmenorrhea was found. In a young Japanese population, underweight—but not overweight—was independently and positively associated with dysmenorrhea.