Background: Several population based studies have demonstrated an association between hypo-or hyperthyroidism and dementia in last two decades. As a consequence, thyroid stimulating hormone has become part of the screening laboratory test for dementia. Aim: The aim of the present study was to evaluate the association between thyroid function and Alzheimer′s disease (AD) and vascular dementia (VaD) and to determine the risk of AD and VaD in clinically euthyroid patients. Materials and Methods: A cross-sectional hospital based study was carried out in subjects diagnosed with AD/VaD and were assessed for thyroid status as routine screening test. Results: Free T3, free T4 and TSH were studied in 114 AD patients (mean age: 65 years), 35 VaD patients (mean age: 62 years) and 105 control subjects (mean age: 62 years). In AD group, TSH levels were significantly lower than controls (P = 0.00) and for each unit increase in TSH level, the odds of having dementia decreased by 37.1%. No such relation was seen in VaD. Conclusion: The results suggest a consistent association of subclinical hyperthyroidism and AD
