Cardiovascular disease risk factors in postmenopausal women: excess iron is related to central adiposity but not to oxidative stress
Postmenopausal women are at risk of atherosclerotic cardiovascular disease (CVD) due to a decrease in circulating estrogen levels, compromised antioxidant status, and an increase in iron stores, oxidative damage, and abdominal fat accumulation. The objective of our study was to determine the relationship among excess iron, oxidative stress, and central adiposity in postmenopausal women. Healthy postmenopausal women were recruited for the Soy Isoflavones for Reducing Bone Loss study, a randomized, double-blind, clinical trial designed to examine the effect of soy isoflavones on bone. Antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase), iron stores (serum ferritin [SF], and other indices), oxidative stress (oxidized LDL [oxLDL], urinary isoprostanes [PGF[subscript 2a]], protein carbonyls, DNA damage), and body size and composition (body mass index [BMI], waist circumference [WC], waist-to-hip ratio [WHR], sagittal diameter, androidal-to-gynoidal fat mass ratio [AGF]) were measured at baseline (n=122). Insulin resistance was calculated using the homeostasis model assessment (HOMA). Pearson correlation and multiple regression analyses were used to determine the contributing CVD risk factors to oxidative stress and central adiposity. Iron status was normal based on median SF (53.1 ng/mL), hemoglobin (13.7 g/dL), and transferrin saturation (24%) in these women. Subjects had a median BMI=24.9 kg/m2 and WHR=0.75; fasting insulin (12.8 mU/mL) and glucose (87.0 mg/dL) were within normal limits. Excess iron was not related to oxidative stress but was related positively to central adiposity (AGF [r=0.28, P<0.0l], waist fat mass [r=0.24, P<0.01], sagittal diameter [r=0.18, P<0.05], WHR [r=0.33, P<0.001]), HOMA (r=0.21, P<0.05), and age (r=0.23, P<0.05). Lipid oxidation measures were also associated positively with central adiposity. Multiple regression analysis revealed age, LDL cholesterol, and AGF were contributors to the overall variance (R2=34.4%; P(less than or equal to)0.0001) in oxLDL, whereas oxLDL, time since menopause, HOMA, HDL cholesterol, PGF[subscript 2a], and SF contributed to the overall variance (R2=33.0%; P(less than or equal to)<0.0001) in AGF. Future studies are needed to determine how iron status, insulin resistance, and oxidative stress are related to central adiposity. Soy foods contain compounds, such as isoflavones, with antioxidant effects that may protect against oxidative stress (decrease oxidative damage and/or improve antioxidant enzymes) and thus may decrease CVD risk.