Puberty, body fat, and breast density in girls of several ethnic groups.

OBJECTIVES: We examined breast density by dual energy X-ray absorptiometry (DXA) in relation to pubertal maturation and body fatness among girls of several ethnic groups, which may suggest important risk factors for future breast cancer.
METHODS: Recruiting 113 girls from Kaiser Permanente Hawaii, we determined ethnicity, age at menarche, weight, height; body mass index (BMI), BMI Z-scores, Tanner breast, and pubic hair pubertal stages (and classified stages for synchrony, thelarche or adrenarche). DXA scans of the whole body provided percent total and segmental body fat; and separate (specially calibrated) breast scans provided breast tissue, total area, and volume (from manual delineation); absolute and percent fibroglandular volume (%FGV, or breast density) were computed. Statistical analysis included correlation, chi-square tests, ANOVA, and stepwise regression.
RESULTS: Twenty-six percent of girls were overweight or obese. Higher BMI was associated with greater breast area, breast volume, FGV, and with lower breast density (P < 0.0001). Breast area, breast volume, and FGV were positively associated with Tanner breast stage (P < 0.001). Breast density increased until Tanner breast Stage 4 but was lower in Stage 5 (P = 0.03). Pubertal thelarche was associated with lower breast density, compared to synchrony or adrenarche (P = 0.03). Girls with higher BMI (P = 0.02), and Asian girls (compared to White, P = 0.04) were more likely to have pubertal thelarche. Determinants of breast density were, in (stepwise regression) order, percent body fat, achieved menarche, BMI Z-score, Tanner breast stage (non-linear), and "Other" ethnicity.
CONCLUSIONS: Female adolescent breast density was negatively associated with body fatness and positively associated with menarche.