Metrics of diabetes risk are only minimally improved by exercise training in postmenopausal breast cancer survivors

Context Insulin resistance is a risk factor for breast cancer recurrence.
How exercise training changes fasting and post-glucose insulin resistance
in breast cancer survivors is unknown. Objective To evaluate
exercise-induced changes in post-glucose ingestion insulin concentrations,
insulin resistance, and their associations with cancer-relevant biomarkers
in breast cancer survivors. Setting The University of Massachusetts
Kinesiology Department. Participants Fifteen postmenopausal breast cancer
survivors not meeting the physical activity guidelines (150 minutes/week
of exercise). Intervention a supervised 12-week aerobic exercise program
(60 min/day, 3-4 days/week). Main outcome measures Post-glucose ingestion
insulin was determined by peak insulin and area under the insulin curve
(iAUC) during a five-sample oral glucose tolerance test. Insulin
sensitivity was estimated from the Matsuda composite insulin sensitivity
index (C-ISI). Changes in fitness and body composition were determined
from submaximal VO2peak and dual energy X-ray absorptiometry
(DEXA). Results Participants averaged 156.8±16.6 minutes/week of
supervised exercise. Estimated VO2peak significantly increased
(+2.8±1.4 ml/kg/min, p<0.05) and body weight significantly
decreased (-1.1±0.8 kg, p<0.05) following the intervention. There
were no differences in fasting insulin, iAUC, C-ISI or peak insulin
following the intervention. Insulin was only significantly lower 120
minutes following glucose consumption (68.8 ± 34.5 vs. 56.2 ± 31.9 uU/ml,
p<0.05), and there was a significant interaction with past/present
aromatase inhibitor (AI) use for peak insulin (-11.99 (non-AI) vs +13.91
(AI) uU/mL) and iAUC (-24.03 (non-AI) vs +32.73 (AI) uU/mL). Conclusions
Exercise training had limited overall benefits on insulin concentrations
following glucose ingestion in breast cancer survivors but was strongly
influenced by AI use.