Age-related changes in fat deposition in mid-thigh muscle in women: relationships with metabolic cardiovascular disease risk factors.

OBJECTIVE: To determine if fat deposition within mid-thigh muscle, represented by low density lean tissue density, is associated with age, low physical fitness, hyperleptinemia, hyperinsulinemia and dyslipidemia in women.
SUBJECTS: Seventy-two women aged 18-69y with a wide range of total body fat (10-55%) and maximal aerobic capacity (VO2max: 17-61 ml/kg(-1)/min(-1)). MEASUREMENTS: Mid-thigh muscle, mid-thigh fat, low density lean tissue, intra-abdominal adipose tissue (IAAT) and subcutaneous abdominal fat (by computed tomography, CT), fat mass (FM) and fat-free mass (FFM) (by dual energy x-ray absorptiometry, DEXA), plasma insulin and leptin (by radioimmunoassay, RIA) and lipoprotein lipid profiles (by enzymatic methods).
RESULTS: VO2max declined with age (r=-0.59, P<0.0001) while IAAT and subcutaneous abdominal fat increased with age (r=0.68, r=0.57, r=0.63, P<0.0001). Mid-thigh low density lean tissue correlated with age (r=0.52), VO2max (r=-0.56), FFM (r=0.35), fat mass (r=0.68), IAAT (r=0.66) and subcutaneous abdominal fat (r=0.67, all P<0.005). Mid-thigh low density lean tissue also correlated with fasting plasma leptin, insulin, triacylglycerol (TG), total cholesterol (TC) and low-density-lipoprotein cholesterol (LDL-C) levels (r=0.44, 0.34, 0.41, 0.50, 0.53, respectively, all P<0.005), but not after controlling for body fat and age. Subcutaneous abdominal fat, IAAT, FFM and age were independent predictors of low density lean tissue (P<0.05).
CONCLUSIONS: Mid-thigh low density lean tissue is directly related to age and adiposity. Furthermore, it appears that fat accretion in skeletal muscle adversely influences plasma insulin and lipoprotein metabolism in women, but not independently of total adiposity and age.