Abstract
Background Evidence suggests that recreational physical activity (RPA) during adolescence is associated with lower
breast cancer (BC) risk, but the biological mechanisms underlying this relationship remain unclear. We examined
the associations between RPA and three BC biomarkers–breast tissue composition (BTC), oxidative stress, and
inflammation–in adolescent girls. We also investigated how oxidative stress and inflammation relate to BTC during
this developmental stage.
Methods We analyzed data from a population-based urban cohort of 191 Black/African American and Hispanic
(Dominican) adolescent girls (ages 11–20 years). Participants reported the number of hours they participated in
organized and unorganized RPA in the past week, categorized as none, < 2 h, and ≥ 2 h. We used optical spectroscopy
to measure BTC: specifically, chromophores that are positively (percent water content and percent collagen
content) or negatively (percent lipid content) correlated with mammographic breast density. We measured urinary
concentrations of 15-F2t-isoprostane, a sensitive and specific marker of oxidative stress, and blood biomarkers of
inflammation, including TNF-α, IL-6, and high-sensitivity C-reactive protein. We used multivariable linear regression
models to examine associations, adjusting for age, race, ethnicity, and percent body fat.
Results 51% of adolescent girls reported no past-week engagement in any type of RPA; 73% reported no
participation in organized activities, and 66% reported no participation in unorganized activities. Girls who engaged
in ≥ 2 h of organized RPA in the past week, compared to none, had lower percent water content in the breast (β:
− 0.41, 95% CI: − 0.77, − 0.05), and this association was not modified by percent body fat; they also had lower urinary
concentrations of 15-F2t-isoprostane (β: − 0.50, 95% CI: − 0.95, − 0.05). An association was observed between higher
urinary concentrations of 15-F2t-isoprostane and higher percent collagen content in the breast (β: 0.15, 95% CI: 0.00,
0.31). RPA was not associated with the measured inflammatory biomarkers, and these biomarkers were not associated
with BTC after adjusting for percent body fat.