(HealthDay News) – For patients with atrial fibrillation (AF), female gender increases the risk of stroke only in patients aged ≥75 years.

Anders Mikkelsen, from the Copenhagen University Hospital Gentofte in Denmark, and colleagues identified 87,202 non-anticoagulated patients discharged with non-valvular AF from 1997–2008 through national Danish registries. The patients (51.3% women) were divided into three groups based on age: <65, 65–74, and ≥75.

The researchers found that, compared with male patients, the stroke risk was not elevated for females aged <65 or 65–74 years. However, at the one-year follow-up, for patients aged ≥75 years, the stroke rate was 12.08 in women and 9.78 in men. Female gender was not associated with increased risk of stroke for patients <75 years at the one-year or 12-year follow-up. At the 12-year follow-up, the hazard ratio associated with female gender was 0.86 (95% confidence interval [CI], 0.76–0.98) for those <65 years and 0.98 (95% CI, 0.90–1.07) for those aged 65–74 years. At one-year follow-up, the risk associated with female gender for those ≥75 year was approximately 10–20%.

“Our study shows that female gender is only a significant risk factor for stroke among patients aged ≥75 years. Further research may be needed into the contribution of female gender to stroke risk on subjects <75 years of age,” the authors conclude.

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