Background: The long-term risks of stroke associated with hypothyroidism and hyperthyroidism is unknown. We evaluated the long-term risk of stroke with hypothyroidism and hyperthyroidism compared with euthyroid status.
Material/Methods: We used the 20-year follow-up data for adults aged 25 to 74 years who participated in the First National Health and Nutrition Examination Survey Follow-up Study. Hypothyroidism or hyperthyroidism
was diagnosed by free thyroxine index measurements at baseline evaluation and incident events were determined from hospital records and death certifi cates during follow-up. Relative risk (RR) of stroke, ischemic stroke, and intracerebral hemorrhage for each category of thyroid function were determined by Cox proportional hazards analysis after adjustment for potential confounding variables.
Results: A total of 5,269 participants (mean age 48±14 years; 2,379 men) were evaluated. Hypothyroidism and hyperthyroidism were diagnosed in 493 (9.4%) and 34 (0.7%) participants, respectively. After adjustment for covariates, a signifi cantly higher RR for all strokes and for ischemic stroke was observed in participants with hypothyroidism (RR 1.6; 95% confi dence interval (CI), 1.0–2.6 and RR 1.6, 95% CI, 1.0–2.7, respectively). Hyperthyroidism was not associated with an increased risk for
stroke.
Conclusions: An increased risk for stroke (particularly ischemic stroke) was observed in patients with hypothyroidism.

Keywords: Data Collection, Follow-Up Studies, Hyperthyroidism - complications, Hypothyroidism - complications, Proportional Hazards Models, Risk Factors, Stroke - etiology, Thyroxine - blood, United States - epidemiology