Thyroid Function and the Risk of Alzheimer DiseaseThe Framingham Study

Open Access
Publisher Website
Google Scholar
Abstract
Growing evidence links alterations in the endocrine system to the pathogenesis of Alzheimer disease (AD) and other dementias. Insulin resistance,1 elevated cortisol levels,2 and low estrogen3 and testosterone4 levels have all been implicated by multiple studies in the development of dementia. Clinical hypothyroidism and hyperthyroidism have long been recognized as potentially reversible causes of cognitive impairment,5,6 and the serum thyrotropin level has become a standard screening test for the routine evaluation of patients with suspected dementia.7 Furthermore, several cross-sectional studies have observed that high8 or low9 thyrotropin levels in the reference (clinically euthyroid) range are related to poor cognitive performance, although some other investigations10,11 have not demonstrated these associations. More recently, thyroid dysfunction has emerged as a possible risk factor for irreversible dementia, with several epidemiologic studies implicating hypothyroidism12,13 and hyperthyroidism.14 Using prospectively collected data from the Framingham Study, we sought to further elucidate the association between thyroid function and dementia by examining the risk of incident dementia and AD in clinically euthyroid individuals during 12 years of follow-up.