Thyroid hormones are associated with poorer cognition in mild cognitive impairment.
BACKGROUND
Alterations in interrelated endocrine axes may be related to the pathogenesis of mild cognitive impairment (MCI) and dementia.


METHODS
Salivary cortisol before and after a 0.5-mg dexamethasone test, and serum levels of thyroid-stimulating hormone, total thyroxine (T(4)), free T(4), total triiodothyronine (TT(3)), estradiol, testosterone and insulin-like growth factor 1 were measured in 43 MCI cases and 26 healthy controls. All participants underwent a comprehensive neuropsychological test battery covering the cognitive domains of speed/attention, memory, visuospatial functions, language and executive functions.


RESULTS
The MCI group did not differ in basal levels of endocrine markers compared to controls. Among those with MCI, TT(3) levels were inversely associated with cognitive performance across all domains. After stratifying MCI cases according to TT(3) levels, those with relatively high TT(3) levels showed impairment in memory as well as in visuospatial and executive functions. Those with TT(3) levels at or below the lower boundary of the normal range performed comparably to healthy controls. Other endocrine markers were not related to cognitive performance.


CONCLUSIONS
Among those with MCI, TT(3) was associated with a neuropsychological profile typical of prodromal Alzheimer's disease. While the mechanisms remain unclear, optimal levels of thyroid hormone under a compromising condition such as MCI and related neuropathology need reconsideration.
Quinlan
Patrick
P
Institute of Neuroscience and Physiology, Department of Psychiatry and Neurochemistry, Sahlgrenska Academy, University of Gothenburg, Mölndal, Sweden. patrick.quinlan@neuro.gu.se
Nordlund
Arto
A
Lind
Karin
K
Gustafson
Deborah
D
Edman
Ake
A
Wallin
Anders
A
D000368:Aged; D000647:Amnesia / Q000097:blood / Q000523:psychology; D001288:Attention / Q000502:physiology; D003072:Cognition Disorders / Q000097:blood* / Q000523:psychology*; D056344:Executive Function / Q000502:physiology; D005260:Female; D012739:Gonadal Steroid Hormones / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D011597:Psychomotor Performance / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012463:Saliva / Q000737:chemistry; D013963:Thyroid Hormones / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood
D012739:Gonadal Steroid Hormones; D013963:Thyroid Hormones; D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I; D006854:Hydrocortisone
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