Thyroid hormones, dementia, and atrophy of the medial temporal lobe.
BACKGROUND
Thyroid function has been related to Alzheimer disease (AD), but it remains unclear whether thyroid dysfunction results from or contributes to developing AD.


OBJECTIVE
The objective of the study was to determine the association between thyroid function and both medial temporal lobe atrophy on brain magnetic resonance imaging (MRI) as putative early sign of AD and risk of dementia.


METHODS
This was a population-based cohort study among 1077 elderly subjects aged 60-90 yr and dementia free at baseline (1995-1996).


METHODS
Nonfasting serum levels of TSH, free T(4) (fT(4)), T(3), and rT(3) were available in 1025 subjects followed up for incident dementia until 2005. In a subset of 489 nondemented elderly, we assessed volumes of the hippocampus and amygdala on brain MRI. Subjects using thyroid medication were excluded.


RESULTS
During 5657 person-years of follow-up (mean 5.5 yr), 63 subjects were diagnosed with dementia (46 with AD). TSH and thyroid hormones were not associated with risk of dementia or AD. TSH and T(3) were also not related to brain atrophy, whereas nondemented subjects with higher fT(4) levels had more hippocampal and amygdalar atrophy on MRI. Similar associations were found for rT(3). Excluding subjects with thyroid disorders or incipient AD did not change the results.


CONCLUSIONS
In our study, TSH was related neither to risk of AD nor with early MRI markers thereof, arguing against an important role of thyroid function in the development of AD. Whether the association of higher fT(4) and rT(3) levels with brain atrophy on MRI has functional significance remains to be elucidated.
de Jong
Frank Jan
FJ
Department of Epidemiology and Biostatistics, Erasmus Medical Center, 3000 DR Rotterdam, The Netherlands.
den Heijer
Tom
T
Visser
Theo J
TJ
de Rijke
Yolanda B
YB
Drexhage
Hemmo A
HA
Hofman
Albert
A
Breteler
Monique M B
MM
D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000150:complications / Q000453:epidemiology; D000679:Amygdala / Q000473:pathology; D001284:Atrophy; D015331:Cohort Studies; D003704:Dementia / Q000453:epidemiology*; D005500:Follow-Up Studies; D006624:Hippocampus / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D012307:Risk Factors; D013702:Temporal Lobe / Q000473:pathology*; D013959:Thyroid Diseases / Q000150:complications / Q000503:physiopathology; D013961:Thyroid Gland / Q000503:physiopathology; D013963:Thyroid Hormones / Q000097:blood*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D014285:Triiodothyronine, Reverse / Q000097:blood
D013963:Thyroid Hormones; D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D013972:Thyrotropin; D013974:Thyroxine