Circulating SHBG (Sex Hormone-Binding Globulin) and Risk of Ischemic Stroke: Findings From the WHI.

Background and Purpose- Circulating levels of SHBG (sex hormone-binding globulin) have been inversely linked to obesity, diabetes mellitus, and other cardiometabolic disorders. It remains uncertain whether low SHBG is prospectively predictive of stroke risk, particularly in women. We investigated whether SHBG is associated with risk of incident ischemic stroke (IS) among women in the WHI (Women's Health Initiative). Methods- From an observational cohort of 161 808 postmenopausal women enrolled in the WHI at 40 sites across the United States from 1993 to 1998, we identified 13 192 participants free of prevalent stroke at baseline who were included in an ancillary study that measured serum SHBG. We used Cox proportional hazards regression, stratified by SHBG measurement assay, to assess IS risk across quintiles of SHBG (Q1-Q5), adjusting first for demographic variables (model 1), additionally for body mass index, hypertension, alcohol use, and smoking status (model 2), and for physical activity and reproductive risk factors (model 3). In sensitivity analyses, potential mediators (diabetes mellitus status, levels of estradiol, testosterone, and CRP [C-reactive protein]) were included. Results- Of 13 192 participants (mean age, 62.5 years; 67.4% non-Hispanic white, 18.5% black, 7.6% Hispanic, and 5.0% Asian), after following for an average of 11.6 years, 768 IS events were adjudicated. Compared with the highest quintile of SHBG levels (referent), women in the lowest SHBG quintile had a higher risk of IS in all 3 multivariable models (model 1: hazard ratio, 1.88 [95% CI, 1.47-2.41]; model 2: hazard ratio, 1.69 [95% CI, 1.30-2.20]; model 3: hazard ratio, 1.61 [95% CI, 1.19-2.19]; trend tests P<0.05 for all models). Including potential mediators such as diabetes mellitus, estradiol, and testosterone in the models attenuated but did not eliminate significant inverse associations between SHBG and IS. Conclusions- In this prospective cohort of postmenopausal women, there was a statistically significant inverse association between serum SHBG levels and IS risk, which supports the notion that SHBG could be used as a risk stratification tool for predicting IS in women.