Subclinical hyperthyroidism and dementia: the Sao Paulo Ageing & Health Study (SPAH)

A cross-sectional study - S？o Paulo Ageing & Health Study (SPAH) - in a population sample of low-income elderly people ≥ 65 years-old to evaluate presence of subclinical thyroid disease as a risk factor for dementia. Thyroid function was assessed using thyrotropic hormone and free-thyroxine as well as routine use of thyroid hormones or antithyroid medications. Cases of dementia were assessed using a harmonized one-phase dementia diagnostic procedure by the "10/66 Dementia Research Group" including Alzheimer's disease and vascular dementia. Logistic regression models were used to test a possible association between subclinical hyperthyroidism and dementia.Prevalence of dementia and of subclinical hyperthyroidism were respectively of 4.4% and 3.0%. After age adjustment, we found an association of subclinical hyperthyroidism and any type of dementia and vascular dementia (Odds Ratio, 4.1, 95% Confidence Interval [95% CI] 1.3-13.1, and 5.3 95% CI, 1.1-26.4; respectively). Analyzing data by gender, we found an association of subclinical hyperthyroidism with dementia and Alzheimer's disease only for men (OR, 8.0; 95% CI, 1.5-43.4; OR, 12.4; 95% CI, 1.2-128.4; respectively). No women with subclinical hypothyroidism presented Alzheimer's disease in the sample.The results suggest a consistent association among people with subclinical hyperthyroidism and dementia.Thyroid disease and dementia are relatively common in elderly people. However, the diagnosis is difficult as symptoms can be vague and clinical presentation is confounded by the ageing process. Due to the close association between thyroid function and cognitive performance, the hypothesis thyroid dysfunction may be a risk factor for cognitive impairment has been investigated with conflicting results [1-10]. The Leiden-85 study did not show any association between levels of thyroid stimulating hormone (TSH) and free thyroxine (FT4) [1] with cognitive impairment. However, the Women's Health and Aging Study reported cog