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Published on: October 6, 2023
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Association Between Subclinical Thyroid Dysfunction and Cognitive Decline: Findings From the ELSA-Brasil Study
Natalia Gomes Gonçalves1, Claudia Szlejf2, Paulo Andrade Lotufo2
1Division of Geriatrics, Faculdade de Medicina, Universidade de São Paulo, São Paulo, São Paulo, Brazil.
Summary
Subtle changes in free thyroxine (FT4) levels over time, even without overt thyroid dysfunction, were linked to accelerated cognitive decline in adults. Both increases and decreases in FT4 were associated with faster declines in memory, verbal fluency, and executive function.
Area of Science:
- Endocrinology
- Neuroscience
- Gerontology
Background:
- Thyroid dysfunction is a known factor in cognitive decline and dementia.
- The specific impact of subtle thyroid hormone variations on cognition remains unclear.
- This study investigates the longitudinal relationship between thyroid hormones and cognitive function in individuals without overt thyroid disease.
Purpose of the Study:
- To examine the association between baseline and changes in thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) levels and cognitive decline.
- To assess cognitive performance over time in a cohort of middle-aged and older adults without overt thyroid dysfunction.
- To determine if subtle thyroid hormone alterations predict cognitive decline.
Main Methods:
- Longitudinal study with 9,524 participants aged 35-74 years, evaluated over three waves (2008-2019).
- Assessed baseline TSH, FT4, and FT3 levels.
- Cognitive function evaluated every 4 years using tests for memory, verbal fluency, executive function, and word recognition, with a global composite z-score derived.
- Linear mixed-effect models were used to analyze associations, adjusting for relevant covariates.
Main Results:
- No association was found between baseline TSH, FT4, or FT3 levels and cognitive decline.
- An increase in FT4 levels over time correlated with faster decline in memory, verbal fluency, executive function, and global cognition.
- A decrease in FT4 levels over time was associated with faster decline in verbal fluency and executive function.
Conclusions:
- Changes in free thyroxine (FT4) levels over time, not just baseline levels, are associated with cognitive decline.
- Both increasing and decreasing FT4 levels were linked to accelerated cognitive decline in middle-aged and older adults without overt thyroid dysfunction.
- These findings highlight the importance of monitoring FT4 levels for cognitive health in aging populations.
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