Height and breast cancer risk in premenopausal Korean women aged under 40 years of age

Taller women are at an increased risk of breast cancer; however, evidence regarding this in younger women is limited. This study investigated the association between body height and breast cancer risk in premenopausal Korean women aged <40 years. Premenopausal women aged <40 years enroled in the Kangbuk Samsung Health Study (KSHS) and National Health Insurance Service-National Health Information Database (NHIS-NHID) were included in the analysis. Trained staff members performed anthropometry, including height measurements. Breast cancer incidence was followed up until December 2019. Cox regression model and restricted cubic- spline regression were applied. The mean (standard deviation [SD]) age was 33.3 (3.6) years and 32.9 (4.2) in KSHS and NHIS-NHID cohorts, respectively. After adjusting for age at baseline and other confounders, every 10 cm of height was associated with a 1.44-fold increased risk of developing breast cancer (adjusted hazard ratio [aHR], 1.44; 95% confidence interval [CI], 1.17–1.78) in the KSHS. The restricted cubic spline regression showed an almost linear association between height and breast cancer risk. Compared to women with height <155 cm, aHRs (95% CI) among those with height 160–165 cm, 165–170 cm, and ≥170 cm were 1.67 (1.07–2.60), 1.75 (1.09–2.81), and 2.31 (1.18–3.86), respectively (P = 0.009). Results were similar in the NHIS-NHID cohort (aHR, 1.20 [95% CI, 1.10–1.31] per 10-cm increase in height). In young Korean women, greater body height was associated with increased breast cancer risk.