Subclinical Hypothyroidism 101: Causes Brain to Shrink?
- Study looked at 2500 patient’s brain images.
- TSH > 3.3 was considered subclinical hypothyroid.
- These patients had significantly lower brain volume.
- The part of the brain was the Hippocampus and brain white matter.
- What does it mean? Too early to tell but any loss of brain tissue is not good.
- Hippocampus resembles a seahorse and is located on both halves.
- It plays a major part in short and long term memory and spatial memory.
- How many of us need to loose short term or long term memory?
- Subclinical hypothyroidism has reasons for considering thyroid hormone thery to normalize the TSH even iif you are not symptomatically hypothyroid.
Background: Previous patient studies suggest that thyroid dysfunction affects volumes of particular regions of the brain. So far, population-based data related to this topic are lacking. The aim of this study was to investigate associations of serum levels of thyrotropin (TSH), free triiodothyronine, and free thyroxine (fT4) with total brain volume, gray matter volume, white matter volume (WMV), and hippocampal volume (HV) in a population-based study.
Methods: Data on 2557 individuals were pooled from two independent population-based surveys of the Study of Health in Pomerania conducted in Northeast Germany. Brain volumes were determined from images derived from 1.5 T magnetic resonance imaging. Low and high TSH were defined using the cutoffs 0.40 and 3.29 mIU/L, respectively. Associations between thyroid hormone levels and segmented brain volumes were analyzed by linear regression models. Further, voxel-based morphometry was conducted to search for associations with thyroid hormone levels in a hypothesis-free way throughout the whole brain. All models were adjusted for confounders.
Results: Only 9/70 individuals with high TSH had low free triiodothyronine or fT4 levels. Individuals with high TSH had significantly lower total brain volume (β = −26.9 [confidence interval (CI) −49.0 to −4.8]; p = 0.017), WMV (β = −16.1 [CI −29.4 to −2.7]; p = 0.018), and HV (β = −223 [CI −395 to −50]; p = 0.011) than individuals with TSH within the reference range, while low TSH was not significantly associated with any of the brain volumes. Voxel-based morphometry analyses revealed a significant positive association with serum fT4 levels in the left middle frontal gyrus.
Conclusions: In conclusion, the results of this study indicate that the subclinical hypothyroid state may lead to a reduced brain volume affecting particularly HV in younger subjects and WMV, which might correspond to subtle microstructural changes in white matter fiber tracts or myelination of the axones. Gray matter seems not to be affected by subclinical hypothyroid states.