Association of calcium and vitamin D intakes with mammographic density in twins.

B164

Introduction: Calcium and vitamin D have effects on cellular proliferation and differentiation that may reduce breast cancer risk. Some cross-sectional studies have reported that higher intakes of these nutrients are associated with lower mammographic density, a strong risk factor for breast cancer. Specific Aim : The goal of this research was to examine the association of calcium and vitamin D intakes with percent mammographic density using a co-twin study design to control for the strong genetic influence on mammographic density. Methods: The analysis included twins recruited in North America (351 twin pairs, 62% monozygous) and in Australia (408 twin pairs, 61% monozygous). Percent mammographic density was measured using a computer-assisted method and nutrient intakes from food and supplements were measured using food frequency questionnaires. The associations of twin-pair differences in mammographic density with calcium and vitamin D intakes were examined using simple and multiple linear regression analysis. Results: In North American twins, percent density was significantly positively correlated with calcium and vitamin D intakes from food before (p=0.005 and p =0.03 respectively), but not after (p=0.57 and p=0.81 respectively), adjustment for potential confounders (age at mammogram, zygosity, height, weight, parity, menopausal status, HRT use, smoking and total energy intake). In Australian twins, a negative correlation between percent density and calcium intake was observed (p=0.03) which remained of borderline statistical significant after adjustment for potential confounders (p=0.06). Calcium and vitamin D intakes from supplements were not associated with percent density. Conclusions: Overall, the results of this study do not provide strong support for an association of calcium and vitamin D intakes with mammographic density.