Postmenopausal African American Women Demonstrate Greater Age-Associated Declines in Lean Tissue Mass Compared to Caucasians

Abstract

Aging is associated with a decline in lean tissue mass (LM). African American (AA) postmenopausal women have higher LM than Caucasians (C). We hypothesized that due to their higher LM, AA women would demonstrate an accelerated decline in LM compared to age-matched C subjects, and the decline in LM would be related to deconditioning (Lower Peak VO2). PURPOSE: To compare the rate of decline in lean body mass with age between postmenopausal AA and C women, and determine if peak VO2 is related to the decline in LM. METHODS: 226 C and 89 AA women of comparable age (58 ± 7 vs. 60 ± 7 yrs, respectively) had total LM and appendicular tissue mass (AM) measured by Dual Energy X-ray Absorptiometry (DXA). Peak VO2 (ml/kg/min) was measured during a progressive graded exercise treadmill test to exhaustion. Group differences were analyzed by Student's t-tests, and relationships were analyzed using Linear Regression. Data are mean ± standard deviation. RESULTS: AA had significantly higher LM (44.3 ± 5.1 vs. 41.3 ± 5.1 kg, p = 0.002) and AM (20.3 ± 2.6 vs. 18.1 ± 2.5 kg, p < 0.001) than C, respectively. Conversely, AA had 12% lower peak VO2 compared to C (p < 0.001). AA also demonstrated a greater rate of decline in LM with age compared to C (-0.34 vs. -0.18 kg of LM/year, p = 0.06), respectively. Aging was associated with a decline in peak VO2 (r = -0.31, p < 0.001), but there was no difference in this decline between AA and C (p = NS). Peak VO2 was significantly associated with LM when adjusting for age (r = 0.42, p = 0.006). However, when controlling for race, peak VO2 was associated with LM in C (r = 0.31, p = 0.014) but not in AA (p = NS). CONCLUSIONS: Postmenopausal AA women demonstrate a higher LM across age compared to C, but tend to have a greater rate of decline in LM with age. Postmenopausal AA women have a significantly lower peak VO2 compared to C. The decline in peak VO2 with age in AA is not associated with the decline in LM. Future research should focus on investigating the mechanisms for the larger rate of decline of LM in postmenopausal AA women with age and develop strategies to attenuate that decline.