BMC Public Health 2005, 5:41 http://www.biomedcentral.com/1471-2458/5/41 Table 2: Distributions of fat free mass, fat free mass index and body weight in white and black men, and in women. The Third National Health and Nutrition Examination Survey (NHANES III 1988–94). Age Groups (yrs) Sample Size Whites Mean ± SE African Americans Mean ± SE P Value FFMI (kg/m2) FFM (kg) Body Weight (kg) Men Men Women Men Women Women 40–49 50–59 60–69 70–79 > 80 40–49 50–59 60–69 70–79 > 80 40–49 50–59 60–69 70–79 > 80 40–49 50–59 60–69 70–79 > 80 40–49 50–59 60–69 70–79 > 80 40–49 50–59 60–69 70–79 > 80 708 573 718 600 455 607 506 581 605 450 708 573 718 600 455 607 506 581 605 450 708 573 718 600 455 607 506 581 605 450 20.64 ± 0.12 21.13 ± 0.11 21.00 ± 0.12 20.68 ± 0.14 19.93 ± 0.12 17.49 ± 0.10 18.07 ± 0.17 18.09 ± 0.12 18.21 ± 0.11 18.09 ± 0.09 64.83 ± 0.52 65.94 ± 0.38 64.42 ± 0.42 61.50 ± 0.43 57.74 ± 0.46 46.90 ± 0.35 47.66 ± 0.46 46.94 ± 0.40 45.59 ± 0.39 43.83 ± 0.27 83.76 ± 1.00 85.35 ± 0.66 83.94 ± 0.73 78.92 ± 0.70 73.25 ± 0.63 65.71 ± 0.66 68.47 ± 0.93 66.86 ± 0.68 64.11 ± 0.74 60.46 ± 0.45 20.91 ± 0.14 20.92 ± 0.15 20.92 ± 0.17 20.33 ± 0.15 19.89 ± 0.32 18.70 ± 0.20 18.71 ± 0.22 19.26 ± 0.29 18.93 ± 0.25 18.34 ± 0.32 65.30 ± 0.61 64.29 ± 0.59 63.23 ± 0.66 60.36 ± 0.65 57.23 ± 1.32 50.28 ± 0.66 49.59 ± 0.69 50.15 ± 0.69 48.01 ± 0.62 45.04 ± 0.83 82.10 ± 1.00 81.13 ± 1.03 80.41 ± 1.13 76.91 ± 1.09 72.77 ± 2.07 71.71 ± 1.41 71.83 ± 1.38 72.33 ± 1.09 68.44 ± 1.07 61.93 ± 1.62 0.153 0.265 0.704 0.059 0.904 <0.001 0.026 <0.001 0.014 0.432 0.550 0.012 0.139 0.124 0.715 <0.001 0.013 0.001 0.002 0.143 0.252 <0.001 0.013 0.097 0.834 <0.001 0.031 <0.001 0.002 0.365 Note: statistical significance was set at P ≤ 0.05; Whites and African Americans refer to respective ethnic groups of non-Hispanic origin. FFM indicates fat free mass; FFMI indicates fat free mass index; and BMI indicates body mass index. and in women, and of FFM with ethnicity in women only (Table 3). Although, knowledge of the exact mechanisms leading to ethnic differences in muscle mass remains rudimentary, differences in androgenic activity have been suggested to play an important role. For example, Dowling and Pi- Sunyer reported higher levels of testosterone and sex hor- mone binding globulin in obese black women compared to obese white women [21]. Moreover, a 3- to 4-fold higher allele frequency in the human myostatin gene (GDF8 – a gene which codes for muscle mass) was reported in Blacks compared to Whites [22]. Higher FFM and FFMI in black women compared to white women despite lower levels of physical activity (a major determi- nant of FFM) lend additional support to the presence of important contributing factors at the molecular level. Age-related changes FFM declined with advancing age starting earlier in black men compared to white men, but earlier in white women than black women (Figures 1). Using age as a continuous variable, Regression analysis showed significant decline in FFM and FFMI with increasing age in women (P < 0.001; Page 6 of 9 (page number not for citation purposes)