Insulin sensitivity in postmenopausal women - Independent and combined associations with hormone replacement, cardiovascular fitness and body composition

OBJECTIVE - The effects of combined physical activity and hormone replaceme nt therapy (HRT) on insulin sensitivity in postmenopausal (PM) women are un clear. The purpose of the study was to test the following hypotheses: 1) PM women who have undergone vigorous exercise training have greater insulin s ensitivity than PM women who are physically active and PM. women who are se dentary and 2) PM women using HRT have greater insulin sensitivity than PM women not using HRT. We also sought to determine whether body composition o r cardiovascular fitness was the stronger predictor of insulin sensitivity in these women. RESEARCH DESIGN AND METHODS - Three groups of PM women classified as sedent ary (n = 18), physically active (n = 19), and athletic (n = 23) underwent a n insulin-modified frequently sampled intravenous glucose tolerance test to determine the insulin sensitivity index (S-l) and dual-energy X-ray absorp tiometry to determine body composition. RESULTS - There was a significant association between both physical activit y (P = 0.036) and HRT (P = 0.007) and Easting plasma insulin levels. The at hletic PM women had the lowest plasma insulin levels and the highest S-l. A cross all physical activity levels, PM women using HRT (n = 29) had signifi cantly lower fasting plasma insulin levels and a lower S-l than PM women no t using HRT (n = 31), HRT was significantly (P = 0.025) associated with int ravenous glucose tolerance (K-G); the women not using HRT had a higher K-G than the PM women using HRT (0.83 +/- 0.08 vs. 0.60 +/- 0.05% per minute). Percent body fat (r = -0.37, P = 0.004) and V-O2max (r = 0.35, P = 0.007) w ere similar predictors of S-l. CONCLUSIONS - We conclude that, although overall HRT was associated with an attenuated S-l, vigorous exercise training was independently associated wi th the greatest S-l. In addition, PM women using HRT may benefit from havin g lower plasma insulin levels, but they may also have a lower S-l.