Endocrinology
Is a mildly overactive thyroid linked to dementia in older adults?
Open access · cc by · source: Europe PMC
Older Brazilians whose blood tests showed a mildly overactive thyroid were about four times as likely to have dementia, mainly vascular dementia, as those with normal thyroid function.
Study at a glance
- Design
- Cross-sectional — Cross-sectional analysis of the baseline wave of a door-to-door population cohort, with logistic regression of dementia on thyroid status and TSH/FT4 quintiles, adjusted for age and BMI.
- N
- N=1276 · 1,276 participants aged 65+ with thyroid tests and no overt thyroid disease or thyroid medication; of these, 33 had subclinical hyperthyroidism and 49 had dementia.
- Population
- Adults aged 65 and over living in deprived census areas (shantytowns and Family Health Program households) of Butantan, Sao Paulo, Brazil
- Outcome
- Presence of dementia (any type), Alzheimer's disease and vascular dementia diagnosed with the 10/66 Dementia Research Group protocol
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Of the 1,276 participants, 33 had subclinical hyperthyroidism and 49 had dementia. After age adjustment, subclinical hyperthyroidism was associated with dementia of any type (odds ratio 4.1, 95% CI 1.3-13.1) and with vascular dementia (OR 5.3), but not with Alzheimer's disease overall; results held after adding BMI. In men only, it was linked to dementia (OR 8.0) and Alzheimer's disease (OR 12.4). Subclinical hypothyroidism showed no association, and the lowest TSH quintile carried higher dementia odds (OR 3.6) only when values below the normal range were included.
Methodology
The researchers used baseline data from the Sao Paulo Ageing & Health Study, which recruited people aged 65 and over by knocking on doors in a poor area of the city. After excluding people without thyroid tests or with overt thyroid disease or thyroid medication, 1,276 participants remained. Fasting blood was tested for TSH and free thyroxine, and dementia and its subtype were diagnosed with a standardized one-phase protocol designed for low- and middle-income countries. Logistic regression compared dementia odds in people with subclinical hyperthyroidism against those with normal thyroid function, adjusting for age and BMI.
Limitations
Because thyroid status and dementia were measured at the same time, the study cannot tell whether thyroid changes came first or whether dementia or its causes altered thyroid function. The key exposure group had only 33 people and there were 49 dementia cases, so the confidence intervals are very wide (the Alzheimer's estimate in men runs from 1.2 to 128.4) and the authors say chance cannot be excluded. Adjustment was limited to age and BMI, lifetime iodine intake was unknown, and about a third of the original cohort had no thyroid data because testing started after recruitment began.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
A mildly overactive thyroid goes with dementia in older people, but the direction is unknown.
Among 1,276 older adults in deprived areas of Sao Paulo, subclinical hyperthyroidism (low TSH, normal FT4) was associated with about four times the odds of dementia (OR 4.1, 95% CI 1.3-13.1), mainly vascular dementia; subclinical hypothyroidism showed no association.
Evidence for the claim as stated.
A mildly overactive thyroid goes with dementia in older people, but the direction is unknown.
Among 1,276 older adults in deprived areas of Sao Paulo, subclinical hyperthyroidism (low TSH, normal FT4) was associated with about four times the odds of dementia (OR 4.1, 95% CI 1.3-13.1), mainly vascular dementia; subclinical hypothyroidism showed no association.
Scope note — Cross-sectional, only 33 exposed people and 49 dementia cases, adjusted only for age and BMI.
Limits the claim's scope: a different population, assay, or outcome.
Which thyroid measure carries the signal differs by outcome and design: in the Rotterdam cohort FT4 predicted macular degeneration while TSH did not, whereas in Sao Paulo the dementia association was defined by low TSH (with the lowest TSH quintile relevant only when below-range values were included). These are different outcomes, populations and designs, so they mark limits rather than a contradiction.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Which thyroid measure carries the signal differs by outcome and design: in the Rotterdam cohort FT4 predicted macular degeneration while TSH did not, whereas in Sao Paulo the dementia association was defined by low TSH (with the lowest TSH quintile relevant only when below-range values were included). These are different outcomes, populations and designs, so they mark limits rather than a contradiction.
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