title: 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 (KLoSHA).
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  Our aim was to investigate the association between thyroid function and the risk of MCI and dementia in euthyroid elderly subjects.
  
  
  METHODS
  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 nondemented 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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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 (nonprogression 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.
  
  
  CONCLUSIONS
  Lower serum TSH level within the reference range was independently associated with the risk of cognitive impairment including MCI and dementia in elderly subjects.
authors.affiliation: Department of Internal Medicine (J.H.M., S.H.C., S.L., H.C.J.) and Neuropsychiatry (T.H.K., J.W.H., K.W.K.), Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam 463-707, Korea; and Department of Internal Medicine (Y.J.P., D.J.P.), Seoul National University Hospital, Seoul National University College of Medicine, Seoul 110-799, Korea.
authors.forename: Jae Hoon
authors.initials: JH
authors.lastname: Moon
authors.forename: Young Joo
authors.initials: YJ
authors.lastname: Park
authors.forename: Tae Hui
authors.initials: TH
authors.lastname: Kim
authors.forename: Ji Won
authors.initials: JW
authors.lastname: Han
authors.forename: Sung Hee
authors.initials: SH
authors.lastname: Choi
authors.forename: Soo
authors.initials: S
authors.lastname: Lim
authors.forename: Do Joon
authors.initials: DJ
authors.lastname: Park
authors.forename: Ki Woong
authors.initials: KW
authors.lastname: Kim
authors.forename: Hak Chul
authors.initials: HC
authors.lastname: Jang
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood*; D044466:Asian People; D003071:Cognition / Q000502:physiology; D003072:Cognition Disorders / Q000097:blood / Q000175:diagnosis* / Q000523:psychology; D003704:Dementia / Q000097:blood / Q000175:diagnosis* / Q000523:psychology; D018450:Disease Progression; D005260:Female; D006306:Health Surveys; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D009483:Neuropsychological Tests; D056910:Republic of Korea; D012307:Risk Factors; D013972:Thyrotropin / Q000097:blood*
chemical_list: D013972:Thyrotropin