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Lower-But-Normal Serum TSH level Is Associated With the Development or Progression of Cognitive Impairment in Elderly: Korean Longitudinal Study on Health and Aging
Moon JH1, Park YJ, Kim TH, Han JW, Choi SH, Lim S, Park do J, Kim KW, Jang HC.
J Clin Endocrinol Metab. 2014 Feb;99(2):424-32 PMID: 24285689
The association between subclinical hyperthyroidism and the risk of dementia has been validated in several studies. However, the effect of thyroid function within reference range on the risk of cognitive dysfunction including mild cognitive impairment (MCI) and dementia is still unclear.: We conducted a population-based prospective study as a part of the Korean Longitudinal Study on Health and Aging. A total of 313 participants who were euthyroid and non-demented at baseline and completed cognitive function tests at a 5-year follow-up evaluation (mean age 72.5 ± 6.9 y) were analyzed in the present study.: Baseline thyroid function was compared according to the development of MCI or dementia during the study period. Binary logistic regression analysis was performed to investigate the independent association between thyroid function and cognitive impairment.
At baseline evaluation, 237 subjects were cognitively normal, and 76 subjects had MCI. Diagnoses of cognitive function in 259 subjects remained unchanged or improved during the study period (non-progression group), whereas 54 subjects showed progression of cognitive impairment to MCI or dementia (progression group). In the progression group, baseline serum TSH levels were lower than those in nonprogression group. Baseline serum free T4 levels were not significantly different between these two groups. The association between lower baseline serum TSH levels and the development of MCI or dementia was maintained after adjustment for conventional baseline risk factors.
Lower serum TSH level within the reference range was independently associated with the risk of cognitive impairment including MCI and dementia in elderly subjects.
| Comment- Maybe a chicken and/or egg question. SC hyperthyroidism, that is, low TSH with normal range FT4, and now low TSH within the normal range, are associated with developing dementia. Or is it the other way around? It is very possibly that dementia represents one fiorm of the Non-Thyroidal Illness Syndrome, and via altered hypothalamic function, leads to lower TSH levels. This interpretation fits with the observed low TSH levels, but normal thyroid hormone levels.