Low thyroid-stimulating hormone as an independent risk factor for Alzheimer disease

Objective: To assess a possible relationship between thyroid-stimulating hormone (TSH) levels, vascular risk factors, and Alzheimer disease (AD). Methods: TSH levels were measured in 178 AD patients (35 confirmed post mortem) and 291 cognitively screened control subjects who were all euthyroid (TSH: 0.5 to 6 mU/L). The risk of AD was determined in participants with lower levels of TSH, several cerebrovascular risk factors, and other potential confounds. Results: AD patients had significantly lower levels of TSH than control subjects. Lowered TSH was associated with a more than twofold increased risk of AD (odds ratio = 2.36, 95% CI = 1.19 to 4.67), independent of other risk factors. Conclusion: Lowered TSH within the normal range is a risk factor for AD, independent of several cerebrovascular risk factors and confounding variables.