Clinical and subclinical hypothyroidism as well as overt hyperthyroidism in middle-aged and elderly adults are both associated with decreased cognitive functioning as memory, reaction time, and visuospatial organization. Subclinical hyperthyroidism (SH) or low serum concentrations of TSH concentrations have been associated with dementia in previous epidemiological studies, but the association in the elderly has not been established. There is little or no consensus regarding how thyroid function is associated with cognitive performance in the elderly. In this focused review, we have performed an examination between eleven studies from the last five years examining the association between thyroid function and cognitive performance in elderly people, a group who is overrepresented among individuals with minor abnormalities in serum TSH and thyroid hormone concentration. Six of the studies showed a consistent finding of an association between SH with cognitive impairment or dementia. In general, taking into account the largest and most powerfully designed studies, there is a strong body of evidence supporting the association between SH and cognitive impairment. The scarce number of publications on these topics indicates the need of more research especially regarding longitudinal and interventional studies thus hopefully enabling confirmation or rejection of causality between TSH abnormalities and dementia. 1. Background Dementia is a clinical syndrome that is characterized by progressive loss of cognitive capabilities and functional impairment. The population prevalence of dementia is about 1% in individuals aged 60–64 years and increases up to 45% in the most advanced ages of 95 and above [1]. Cognitive performance among older people is complex and dependent of many factors, and in spite of the known effects of clinical thyroid disorders on cognitive function, little is known about the relationship between thyroid hormone (TH) levels and cognitive performance among older people with levels of TH within the normal reference range. Since thyroid hormone concentrations change with age and since cognitive decline is often concomitant with aging, physiological changes in thyroid function might be casually related to changes in cognition during normal aging. A lot of studies have investigated the association between dementia, particularly Alzheimer’s disease (AD), and thyroid function, but the findings are inconsistent [2–9]. Subclinical hyperthyroidism (SH) is a term used to define a clinical condition with reduced serum thyroid stimulating hormone (TSH) level
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