Endocrinology
Is thyroid hormone level linked to macular degeneration?
Open access · cc by · source: Europe PMC
Older adults with higher levels of free thyroid hormone, even within the normal range, were more likely to develop age-related macular degeneration over the following years.
Study at a glance
- Design
- Cohort — Prospective population-based cohort (Rotterdam Study cohorts I and II); baseline TSH and free T4 related to incident AMD graded from repeated fundus photographs using Cox models, plus a bidirectional GWAS look-up for shared genetic variants.
- N
- N=5573 · 5,573 participants aged 55 and over without AMD at baseline who had thyroid measurements and follow-up eye exams; 805 developed AMD. The genetic sub-analysis used 4,646 participants with genotype data.
- Population
- Mainly Caucasian adults aged 55 years and older living in Ommoord, a suburb of Rotterdam, the Netherlands.
- Outcome
- Incident early or late age-related macular degeneration (AMD) and specific AMD lesions (retinal pigment alterations, large drusen).
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Of 5,573 participants followed for a median of 6.9 years, 805 developed AMD. TSH was not related to AMD risk (HR 0.99), but higher FT4 was: people in the highest normal-range FT4 quintile had a higher risk than those in the middle quintile (HR 1.34). This held after adjusting for vascular risk factors, when restricted to people with fully normal thyroid function, and after excluding thyroid medication users. Higher FT4 was also linked to retinal pigment changes, an early AMD lesion, and the only shared genetic variant (in VEGF-A) did not explain the association.
Methodology
The researchers used a long-running Dutch population cohort of people aged 55 and over. They measured thyroid-stimulating hormone (TSH) and free thyroxine (FT4) in blood at baseline, excluded anyone who already had macular degeneration, and then graded retinal photographs at repeated follow-up visits. They estimated the risk of developing AMD across levels of each hormone, adjusting for age, sex, smoking, blood pressure, cholesterol, diabetes and BMI, and checked whether genetic variants for thyroid function and AMD overlapped.
Limitations
Thyroid hormones were measured only once at baseline, so the study cannot tell whether changes over time matter, and residual confounding is possible despite adjustment. It shows an association rather than proof that thyroid hormone damages the retina; the proposed mechanisms come mainly from mouse studies. The cohort was mostly white Europeans aged 55 and over, so results may not generalise, and the p-value for the overall quintile trend was not significant, making the size of the effect uncertain.
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.
Where you sit inside the normal range can still matter for risk.
In a prospective Rotterdam cohort of 5,573 adults aged 55+, higher FT4 even within the normal range predicted incident age-related macular degeneration (highest vs middle quintile HR 1.34), while TSH did not.
Evidence for the claim as stated.
Where you sit inside the normal range can still matter for risk.
In a prospective Rotterdam cohort of 5,573 adults aged 55+, higher FT4 even within the normal range predicted incident age-related macular degeneration (highest vs middle quintile HR 1.34), while TSH did not.
Scope note — Single baseline measurement, mostly white Europeans, and the overall quintile trend was not significant.
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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