The findings provide new insights into how physical activity during adolescence—a critical period of breast development—may influence biological pathways linked to future breast cancer risk.

In adult women, higher levels of recreational physical activity (RPA) have consistently been associated with a reduced risk of breast cancer, with studies indicating an approximate 20 per cent lower risk among the most physically active women compared with the least active. However, the biological mechanisms underlying this association, particularly earlier in life, have remained poorly understood.

The new study offers some of the first evidence connecting RPA to breast tissue composition and stress-related biomarkers in adolescent girls. The findings have been published in the journal Breast Cancer Research.

“The importance and urgency of this research are underscored by the rising incidence of breast cancer in young women and the alarmingly low levels of recreational physical activity observed both in this study and among adolescents across the United States and globally,” said Rebecca Kehm, PhD, Assistant Professor of Epidemiology at Columbia Mailman School of Public Health and the study’s first author.

“Our findings suggest that recreational physical activity is associated with changes in breast tissue composition and stress biomarkers in adolescent girls, independent of body fat, which could have important implications for breast cancer risk,” she added.

The study found that girls who reported engaging in at least two hours of recreational physical activity in the previous week, compared with none, had lower breast tissue percent water content—an indicator of lower breast density—as well as lower concentrations of urinary biomarkers linked to stress.

These results are consistent with earlier research in adult women showing that higher levels of physical activity are associated with lower mammographic breast density, a well-established predictor of breast cancer risk.

Researchers analysed data from the population-based Columbia Breast Cancer and the Environment Research Program Study, which draws from the Columbia Center for Children’s Environmental Health (CCCEH) Mothers and Newborns birth cohort. Participants were originally recruited between 1998 and 2006 from prenatal clinics at NewYork-Presbyterian and Harlem Hospital, along with affiliated satellite clinics serving urban communities including Washington Heights, Central Harlem and the South Bronx.

During adolescence, participants self-reported their recreational physical activity over the prior week—including both organised and unorganised activities—and attended clinic visits involving blood and urine sample collection, as well as breast tissue assessments.

The average age of participants was 16 years, with 64 per cent identifying as Hispanic. More than half (51 per cent) reported no recreational physical activity in the previous week. Additionally, 73 per cent reported no participation in organised activities, while 66 per cent reported no unorganised physical activity.

“Our research has several strengths, including the use of multiple biomarkers measured in urine, blood and breast tissue,” said Mary Beth Terry, PhD, Professor of Epidemiology at Columbia Mailman School of Public Health and senior author of the study. “We assessed biomarkers of stress and chronic inflammation that are widely validated in epidemiologic research, increasing confidence in our findings.”

She added that the study’s focus on a population-based, urban cohort of Black/African American and Hispanic girls is particularly important, as these groups have historically been underrepresented in research and continue to face disparities in physical activity levels and breast cancer outcomes.

“Our study population of urban Hispanic (Dominican) and non-Hispanic Black/African American adolescent girls is critical to include in breast cancer research,” said Kehm, who is also affiliated with HICCC. “These groups not only face higher risks of developing breast cancer at younger ages and more aggressive subtypes, but they also consistently report lower levels of recreational physical activity compared with their non-Hispanic White peers.”

The authors note that further longitudinal studies are needed to determine how these adolescent biomarkers may translate into breast cancer risk later in life. The findings, they say, underscore the potential importance of promoting physical activity early in development as a possible strategy for breast cancer prevention.