Exercise Training Lowers Postmeal Insulin Concentrations And Cancer-relevant Adipokines In Postmenopausal Breast Cancer Survivors

Abstract

Exercise-induced reductions in fasting insulin are modestly associated with lower cancer risk and improved prognosis in breast cancer survivors, however the impact of exercise training on postmeal insulin concentrations (50-80% of daily insulin exposure) and the relationship between postmeal insulin and cancer-relevant biomarkers is unclear. METHODS: Fifteen postmenopausal breast cancer survivors underwent a supervised, progressive 12-week aerobic exercise program (60 min/day, 2-4 days/week). Baseline and post-intervention concentrations of insulin and cancer-relevant biomarkers (leptin, adiponectin, IGF-1, SHBG and 17-b Estradiol (E2)) were measured during a five-sample oral glucose tolerance test (OGTT) following 24h dietary and physical activity control. Changes in fitness and body composition were assessed by estimated VO2peak during a submaximal exercise test and dual energy X-ray absorptiometry (DEXA) respectively. In addition to each OGTT timepoint (30, 60, 90 and 120 minutes), postmeal insulin responses were determined by area under the insulin curve (iAUC) using the trapezoid method and peak insulin concentration during the OGTT. Intervention effects were evaluated using paired t-tests and linear mixed models with the statistics package R. Data are presented as (mean±SEM). RESULTS: Participants averaged 34.8 training sessions over the 12-week intervention. Estimated VO2peak increased (25.2±1.26 vs 27.7±1.36 ml/kg/min, p<0.05) and body weight decreased (75.55±2.3 vs 74.45±2.7 kg, p<0.05) following the intervention. There were significant reductions in leptin (30.8±5.0 vs. 23.8±3.4 ng/ml, p<0.05), E2 (12.9±1.7 vs. 10.2±1.4 pg/ml, p<0.05) and 120-minute insulin (68.8±9.1 vs. 56.2±8.2 uU/ml, p<0.05) as a result of exercise training. There were no significant differences in iAUC or peak insulin, however the change in peak insulin was inversely associated with change in E2 (r=-0.57, p= 0.04). CONCLUSION: Exercise training lowered adipocyte-derived cancer biomarkers and postmeal (but not fasting) insulin concentrations. The use of fasting insulin alone may underestimate the impact of insulin on cancer recurrence and prognosis following exercise training in breast cancer survivors Supported by: Rays of Hope Center for Breast Cancer Research, Springfield MA