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.