Oxidative stress is associated with C-reactive protein in nondiabetic postmenopausal women, independent of obesity and insulin resistance

Objective Oxidative stress is associated with obesity, metabolic syndrome and inflammation, suggesting it could be an early event in the pathology of chronic diseases. We tested the hypothesis that elevated levels of oxidative stress markers are associated with increased C-reactive protein (CRP) and that this is independent of obesity and insulin resistance. Research design and methods This study was cross-sectional designed and nondiabetic postmenopausal women (n = 1821) with CRP levels ≤10 mg/l was enrolled. The CRP levels were categorized into quartiles from the lowest to the highest concentrations (Q1-Q4). The degree of insulin resistance was determined using the homoeostasis model assessment of insulin resistance (HOMA-IR). We measured oxidative stress using urinary 8-epi-prostaglandin F_2α (8-epi-PGF _2α) and plasma oxidized low-density lipoprotein (ox-LDL). Results After adjustments for age and lifestyle habits, including smoking and drinking, we found higher body mass index (BMI) and HOMA-IR scores in Q2 and Q3 vs Q1. The Q4 BMI and HOMA-IR scores were higher than all other quartiles. The plasma ox-LDL was higher in Q4 than in Q1. Urinary 8-epi-PGF_2α was higher in Q3 and Q4 than in Q1 or Q2. Urinary 8-epi-PGF_2α positively correlated with CRP (r = 0·235, P < 0·001), whereas no correlation was found between ox-LDL and CRP. Multiple linear regression analyses of BMI and HOMA-IR showed that the association between urinary 8-epi-PGF_2α and CRP levels remained significant (P < 0·001). Conclusions Oxidative stress measured by increased concentration of urine 8-epi-PGF_2α is strongly associated with CRP levels. This finding was independent of obesity and insulin resistance in nondiabetic postmenopausal women.