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Subclinical hypothyroidism negatively affects brain volumes, cognitive function
High levels of thyrotropin are linked to a decrease in brain volume, and even subclinical hypothyroidism may lead to reduced hippocampal volume, according to findings published in Thyroid.
“So far, the association between thyroid dysfunction and brain volumes has only been investigated in small patient studies, and it is debatable whether these findings can be extended to the general population,” Hans J. Grabe, MD, head of the department of psychiatry and psychotherapy at University Medicine Greifswald and German Center for Neurodegenerative Diseases, and colleagues wrote. “Against this background, this study aimed to investigate whether high thyrotropin (TSH) levels are associated with lower [gray matter volume], [white matter volume] and [hippocampal volume].”
Grabe and colleagues used data from the Study of Health in Pomerania, a population-based cross-sectional study of German adults, which was made up of three phases from 1997-2001, 2002-2006 and 2008-2012. The researchers examined health records of 2,084 participants younger than 65 years who had undergone whole-body MRI.
The sample size was split into three groups based on TSH levels: the reference group with TSH 0.4 mIU/L to less than 3.29 mIU/L (n = 2,285; median age, 51 years; 53.9% women), the low TSH group with levels less than 0.4 mIU/L (n = 229; median age, 57 years; 56.3% women) and the high TSH group with levels of at least 3.29 mIU/L (n = 70; median age, 49 years; 64.3% women).
The researchers used linear regression models to determine associations between thyroid hormone levels and segmented brain volumes and voxel-based morphometry to determine associations with thyroid hormone levels in the whole brain.
The researchers found that participants in the high TSH group had lower median brain volume than those in the reference group. There were also significant decreases in total brain volume, white matter volume and hippocampal volume among those in the high TSH group (P = .05).
The researchers noted a trend toward lower hippocampal volume in those with low TSH compared with those in the reference group, most notable in adults younger than 50 years, but this did not reach statistical significance.
Voxel-based morphometry analysis revealed that Brodmann area 9 volume was also inversely related to TSH level (P = .032), which the researchers noted could imply that hypothyroidism has a negative effect on cognitive ability, particularly in short-term memory.
“Longitudinal studies are needed to understand better the interaction with age-related parameters and the putative clinical impact of dysregulated thyroid function on brain-related disorders,” the researchers wrote. – by Phil Neuffer
Disclosure: Grabe reports he has received speaker’s honoraria and travel grants from Fresenius Medical Care and Janssen. Please see the study for all other authors’ relevant financial disclosures.