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The aim of this study was to determine the influence of menopause (hypoestrogenism) as a risk factor for oxidative stress.We carried out a cross-sectional study with 187 perimenopausal women from Mexico City, including 94 premenopausal (mean ± SD age, 44.9 ± 4.0 y; estrogen, 95.8 ± 65.7 pg/mL; follicle-stimulating hormone, 13.6 ± 16.9 mIU/mL) and 93 postmenopausal (mean ± SD age, 52.5 ± 3.3 y; estrogen, 12.8 ± 6.8 pg/mL; follicle-stimulating hormone, 51.4 ± 26.9 mIU/mL) women. We measured lipoperoxides using a thiobarbituric acid–reacting substance assay, erythrocyte superoxide dismutase and glutathione peroxidase activities, and the total antioxidant status with the Randox kit. An alternative cutoff value for lipoperoxide level of 0.320 μmol/L or higher was defined on the basis of the 90th percentile of young healthy participants. All women answered the Menopause Rating Scale, the Athens Insomnia Scale, and a structured questionnaire about pro-oxidant factors, that is, smoking, consumption of caffeinated and alcoholic beverages, and physical activity. Finally, we measured weight and height and calculated body mass index.The lipoperoxide levels were significantly higher in the postmenopausal group than in the premenopausal group (0.357 ± 0.05 vs 0.331 ± 0.05 μmol/L, P = 0.001). Using logistic regression to control pro-oxidant variables, we found that menopause was the main risk factor for oxidative stress (odds ratio, 2.62; 95% CI, 1.35-5.11; P < 0.01). We also found a positive correlation between menopause rating score, insomnia score, and lipoperoxides, and this relationship was most evident in the postmenopausal group (menopause scale, r = 0.327 [P = 0.001]; insomnia scale, r = 0.209 [P < 0.05]).Our findings suggest that the depletion of estrogen in postmenopause could cause oxidative stress in addition to the known symptoms.