Thyroid function and cognitive health: rethinking the relationship between “suboptimal” TSH/FT4 levels and cognitive decline
Bibliographic record
Abstract
INTRODUCTION: Controversial hypotheses suggest that "suboptimal" thyroid function - defined as higher-normal thyroid-stimulating hormone (TSH) (2.0 to 4.5 μIU/mL) or low-normal free thyroxine (FT4) - may increase risk of cognitive decline and dementia in older patients. METHODS: We examined this claim using data from the Canadian Comprehensive Assessment of Neurodegeneration and Dementia cohort (ages 50 to 91; cognitive statuses from unimpaired to dementia, rarer subtypes of dementia excluded). Thyroid function was categorized as "optimal" (TSH < 2.0 μIU/mL or FT4 ≥ 16.74 pmol/L) or "suboptimal." Six hundred eighty-eight participants had TSH data, and 476 participants had FT4 data. RESULTS: = 0.0027, p = 0.96). True hypothyroidism was rare; 98.6% of those with elevated TSH had normal FT4. DISCUSSION: These findings do not support claims that higher-normal TSH or low-normal FT4 contribute to cognitive impairment. Caution is warranted against advocating unproven thyroid supplementation for cognitive health. HIGHLIGHTS: No link was found between "suboptimal" thyroid function and cognitive impairment. Higher-normal TSH levels do not indicate dementia risk or hypothyroidism. Among participants with elevated TSH, 98.6% had normal FT4 levels. Redefining TSH cutoffs to 2.0 μIU/mL lacks clinical justification. Findings question the functional medicine approach of thyroid supplementation for cognitive health.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.007 | 0.023 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".