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 VO_2peak and dual energy X-ray absorptiometry (DEXA).

Results

Participants averaged 156.8±16.6 minutes/week of supervised exercise. Estimated VO_2peak 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.