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Randomized Controlled Trial of Aerobic Exercise on Insulin and Insulin-like Growth Factors in Breast Cancer Survivors: The Yale Exercise and Survivorship Study

¹ Yale School of Medicine and ² John B. Pierce Laboratory, New Haven, Connecticut; and ³ Dana-Farber Cancer Institute, Boston, Massachusetts

Requests for reprints: Melinda L. Irwin, Department of Epidemiology and Public Health, Yale School of Medicine, P.O. Box 208034, New Haven, CT 06520-8034. Phone: 203-785-6392; Fax: 203-785-6279. E-mail: melinda.irwin{at}yale.edu

Background: High insulin and insulin-like growth factor-I (IGF-I) levels may be associated with an increased breast cancer risk and/or death. Given the need to identify modifiable factors that decrease insulin, IGF-I, and breast cancer risk and death, we investigated the effects of a 6-month randomized controlled aerobic exercise intervention versus usual care on fasting insulin, IGF-I, and its binding protein (IGFBP-3) in postmenopausal breast cancer survivors.

Methods: Seventy-five postmenopausal breast cancer survivors were identified from the Yale-New Haven Hospital Tumor Registry and randomly assigned to an exercise (n = 37) or usual care (n = 38) group. The exercise group participated in 150 minutes per week of moderate-intensity aerobic exercise. The usual care group was instructed to maintain their current physical activity level. A fasting blood sample was collected on each study participant at baseline and 6 months. Blood levels of insulin and IGF were measured with ELISA.

Results: On average, exercisers increased aerobic exercise by 129 minutes per week compared with 45 minutes per week among usual care participants (P < 0.001). Women randomized to exercise experienced decreases in insulin, IGF-I, and IGFBP-3, whereas women randomized to usual care had increases in these hormones. Between-group differences in insulin, IGF-I, and IGFBP-3 were 20.7% (P = 0.089), 8.9% (P = 0.026), and 7.9% (P = 0.006), respectively.

Conclusions: Moderate-intensity aerobic exercise, such as brisk walking, decreases IGF-I and IGFBP-3. The exercise-induced decreases in IGF may mediate the observed association between higher levels of physical activity and improved survival in women diagnosed with breast cancer. (Cancer Epidemiol Biomarkers Prev 2009;18(1):306–13)

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