The dose-response effects of aerobic exercise on body composition and breast tissue among women at high risk for breast cancer: A randomized trial

Observational data indicate that behaviors that shift energetic homeostasis, such as exercise, may decrease the risk of developing breast cancer by reducing the amount of energydense, metabolically active adipose tissue. Between December 2008 and April 2013, we conducted a single-blind, 5-month, clinical trial that randomized premenopausal women at high risk of developing breast cancer to one of three groups: 150 min/wk of aerobic exercise (low dose), 300 min/wk of aerobic exercise (high dose), or control. Body composition was assessed using dual-energy x-ray absorptiometry. Background parenchymal enhancement (BPE) was quantified using computerized algorithms on breast dynamic contrast-enhanced MRI. Over 5 months, compared with the control group: the low-dose and high-dose groups lost -1.5 ± 0.5 and -1.3 ± 0.5 kg of body mass (linear P_trend = 0.032); -1.5 ± 0.4 and -1.4 ±0.3 kg of fat mass (linear P_trend =0.003); -1.3 ±0.3 and -1.4 ± 0.3% of body fat (linear P_trend < 0.001); -15.9 ± 5.4 and -26.6 ± 5.0 cm2 of subcutaneous adipose tissue (linear P_trend < 0.001); and -6.6 ± 1.9 and -5.0 ± 1.9 cm2 visceral adipose tissue (nonlinear P_trend = 0.037). For each -1 cm2 reduction in visceral adipose tissue, BPE decreased by -3.43 ± 1.34 cm2 (P = 0.010) and explained 9.7% of the variability in BPE. Changes in other aforementioned body composition outcomes did not significantly correlate with changes in BPE. These mechanistic data support observational evidence that shifting energetic homeostasis through exercise may alter the risk of developing breast cancer. Additional adequately powered studies are needed to confirm and expand upon our findings that changes in body composition are associated with changes in BPE.