Exercise Dose Effects on Insulin Resistance Indicators in Postmenopausal Women: A Randomized Trial

Abstract

Background: While >= 150 minutes/week of moderate-vigorous physicalactivity is recommended for cancer prevention, the optimal amount forbreast cancer prevention is unknown. Insulin resistance is a candidatebiomarker of breast cancer risk. The objective of the study was todetermine if 300 versus 150 minutes/week of moderate-vigorous aerobicexercise produces stronger improvements in insulin resistanceindicators.Methods: The Breast Cancer and Exercise Trial in Alberta (BETA) was ayear-long, two-center, two-armed, randomized controlled exercise trialbetween June 2010 and June 2013. The setting was a volunteer sample fromCalgary and Edmonton, Canada. Participants were 400 inactive,non-diabetic, postmenopausal women with body mass index of 22 - 40kg/m(2). Interventions were 5 days/week aerobic exercise (3 days/weeksupervised) for 60 minutes/session (high) or 30 minutes/session(moderate) at 65-75% heart rate reserve for >= 50% of each session.The main outcome measures were fasting blood concentrations of insulin,glucose, leptin, adiponectin, and resistin measured at baseline, 6 and12 months.Results: Dose effects were evaluated using linear mixed models adjustedfor baseline biomarker concentrations. High/moderate ratios of geometricmean biomarker concentrations over 12 months ranged from 0.93 to 1.00(all P-values >= 0.05), indicating no dose effect. Among adherent women(n = 137), ratios for insulin, homeostasis model assessment of insulinresistance (HOMA-IR), and leptin were 0.77 - 0.89 (P-values < 0.05),indicating more benefit from the high prescription. There was asignificant dose effect (P-value < 0.05) on resistin and leptin innon-obese and younger women, respectively.Conclusions: Prescribing 300 versus 150 minutes/week ofmoderate-vigorous aerobic exercise to inactive, non-diabetic,postmenopausal women may not produce stronger changes in insulinresistance indicators. Among exercise-adherers, however, a 300minutes/week prescription might provide some additional benefit forbreast cancer prevention.