The effect of exercise intensity on insulin levels in postmenopausal breast cancer survivors

Higher serum levels of glucose, C-peptide and insulin have been linked to poorer breast cancer prognosis and fluctuations of these substances resulting from acute bouts of exercise in breast cancer survivors have not been studied. In this pilot study, 28 postmenopausal women were in 3 groups: controls (n = 10), aromatase inhibitor users (AI, n = 8) and breast cancer survivors not using aromatase inhibitors (BCS, n = 10). Fasting glucose, C-peptide and insulin levels were compared and changes in these substances with acute exercise of different intensities were explored. V0₂peak values were determined and fasting blood samples were obtained. Blood was collected before, immediately after, and 45 minutes after 2 exercise bouts: moderate (45 minutes at 60% V0₂peak) and intense (10 minutes at 85% V0₂peak). Fasting glucose, C-peptide and insulin values, plus HOMA-IR values, were homogeneous between groups. Exercise intensity affected glucose, C-peptide and insulin levels similarly in all 3 groups. For the breast cancer survivor groups combined (n = 19), the pre-post changes and post-recovery changes of glucose and C-peptide were significantly different between the moderate and intense bouts (glucose: p = 0.01 and 0.01; C-peptide: p = 0.04 and 0.04, respectively) showing greater increases in glucose and C-peptide during intense exercise. The pre-post change in insulin approached a significant difference between intensities (p = 0.09) showing a greater increase during intense exercise. Of importance, glucose, C-peptide and insulin levels all transiently increased with intense exercise in breast cancer survivors. In conclusion, more research is warranted on the possible detrimental effects of transiently high glucose, C-peptide and insulin levels induced by intense exercise on breast cancer etiology and prognosis.Education, Faculty ofKinesiology, School ofGraduat