The Clinical Impact of Body Mass Index on Breast Cancer in Korea: A Nationwide Population-Based Cohort Study

ABSTRACT

Purpose@#Although increasing body mass index (BMI) is regarded as a potential risk factor for breast cancer (BC) in postmenopausal women, research on premenopausal women has produced conflicting results. We investigated the association between BMI and BC according to menopausal status in Korean. @*Methods@#We analyzed clinical data from 186,835 women aged 20 years or older between 2003 and 2008 using a sample cohort from the national database in Korea. We identified women newly diagnosed with BC and estimated the risk of BC according to BMI (kg/m2). Subjects were categorized into five groups according to World Health Organization recommendations for Asians underweight, <18.5 kg/m2; normal weight, 18.5–22.9 kg/m2; overweight, 23.0–24.9 kg/m2; obese class I, 25.0–29.9 kg/m2; and obese class II, ≥30.0 kg/m2. @*Results@#1,372 women in the cohort were newly diagnosed with BC. A positive relationship between BMI and BC was detected and the hazard ratio in each group compared with the normal weight group was 0.57 (95% CI, 0.42–0.78), 1.27 (1.11–1.45), 1.25 (1.09–1.44), and 1.28 (0.95–1.73), respectively. BMI was determined to be an important risk factor for BC in postmenopausal women (p for trend was 0.015). We failed to find a significant correlation between BMI and BC in premenopausal women. @*Conclusion@#BMI is positively associated with BC in postmenopausal Korean women.