Thyroid Hormone Homeostasis in Levothyroxine-treated Patients: Findings From ELSA-Brasil
Authors' conclusion
The present results challenge the dogma that treatment with LT4 for hypothyroidism restores TH homeostasis in all patients. A substantial number of LT4-treated patients exhibit repeated FT4 and FT3 levels outside the normal reference range, despite normal TSH levels. Further studies are needed to define the clinical implications of these findings.
Study context
- Population
- Adult Brazilians aged 35–74 years in ELSA-Brasil, followed over 8.2 years (2008–2019)ELSA-Brasil cohort 15,105
- Participants
- 186 vs 243
- Exposure
- Levothyroxine (LT4) initiation vs Continuously treated with LT4
- LT4 initiationn = 186
- Continuously treated with LT4n = 243
- Outcome
- Thyroid hormone (TH) homeostasis (serum TSH, FT4, FT3) in LT4-treated individuals
Methodological detailslongitudinal, 3 observation points
- Longitudinal
- 3 observation points
Main finding
As reported in the abstract
- LT4 initiation: decrease in TSH
- 11% to 19%
- LT4 initiation: increase in free T4 (FT4)
- ≈19%
- LT4 initiation: reduction in free T3 (FT3)
- 7%
- LT4 initiation: FT3 dropped >10%
- ∼40% of patients
- Continuous LT4: ≥1 FT4 above reference range (>1.52 ng/dL)
- 115 (47.3%)
- Continuous LT4: ≥1 FT3 below reference range (<0.23 ng/dL)
- 38 (15.6%)
Observational data: associations, not effects.
Further findings
Metabolic changes after LT4 initiation
- Associated with increase in TG and use of hypolipidemic and antidiabetic medications
Original publication
Thyroid Hormone Homeostasis in Levothyroxine-treated Patients: Findings From ELSA-Brasil. J Clin Endocrinol Metab. Published 20 March 2024. doi:10.
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