Overt thyroid disease means that both the TSH levels and the thyroid hormone levels are abnormal, while subclinical disease is defined by abnormal TSH levels only — the thyroid hormone levels are normal. Overt hypothyroidism and hyperthyroidism has been clearly shown to be associated with a decline in thinking and understanding (cognitive function) and possibly developing early dementia. It is still unclear whether subclinical hypothyroidism and/or hyperthyroidism are similarly associated with worsening cognitive function and early dementia. The aim of this study was to examine published studies to determine whether subclinical hypothyroidism or subclinical hyperthyroidism is associated with increased risk for dementia or impaired thought processes.
THE FULL ARTICLE TITLE:
Rieben C et al Subclinical Thyroid Dysfunction and the Risk of Cognitive Decline: a Meta-Analysis of Prospective Cohort Studies. J Clin Endocrinol Metab. September 30, 2016 [Epub ahead of print].
SUMMARY OF THE STUDY
The authors included studies which involved adults with subclinical hypothyroidism and/or hyperthyroidism as well as people without thyroid disease. An evaluation for early dementia was performed using the Mini Mental State Examination (MMSE) (page 18). A total of 11 studies, including 16,805 participants, were eligible for inclusion. Some reported information on dementia, others reported outcomes from the MMSE and some on both. In most studies the average age of the participants was >70 years and the average follow-up was 44.4 months. Subjects on thyroid hormone or on medications that could change thyroid function were excluded when analyzing the results.