Socioeconomic Status at Birth and Breast Tissue Composition in Adolescence and Adulthood.

Background: Socioeconomic status (SES) at birth is associated with breast cancer risk. Whether this association is driven by changes in breast tissue composition (BTC) prior to adulthood remains unclear.

Methods: We used multivariable linear regression models to examine whether SES at birth is associated with BTC in adolescence and adulthood using data from a New York City cohort of daughters (n = 165, 11-20 years) and mothers (n = 160, 29-55 years). We used maternal-reported data on daughters' household income and maternal education at birth, analyzed individually and in combination (SES index). Women also reported their own mothers' education at birth. We used optical spectroscopy to evaluate BTC measures that positively (water content, collagen content, optical index) and negatively (lipid content) correlate with mammographic breast density, a recognized breast cancer risk factor.

Results: Being in the highest versus lowest category of the SES index was associated with lower lipid content [βadjusted (βadj) = -0.80; 95% confidence interval (CI), -1.30 to -0.31] and higher collagen content (βadj = 0.54; 95% CI, 0.09-0.99) in adolescence. In women with a body mass index (BMI) <30 kg/m2, higher maternal education at birth (≥ vs. < high school degree) was associated with lower lipid content (βadj = -0.57; 95% CI, -0.97 to -0.17), higher water content (βadj = 0.70; 95% CI, 0.26-1.14), and higher optical index (βadj = 0.53; 95% CI, 0.10-0.95).

Conclusions: This study supports that SES at birth is associated with BTC in adolescence and adulthood, although the latter association may depend on adult BMI.

Impact: Further research is needed to identify the socially patterned early life factors influencing BTC.