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Updated: Jan 19, 2026

Author Spotlight: In Vivo Assessment of Thyroid Hormone Disruption Using the THAI Mouse Model
Published on: October 6, 2023
Plasma concentrations of free triiodothyronine predict weight change in euthyroid persons
Emilio Ortega1, Nicola Pannacciulli, Clifton Bogardus
1Phoenix Epidemiological Clinical and Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Department of Health and Human Services, Phoenix, AZ 85016, USA. emilioo@mail.nih.gov
Background:
Factors that influence energy metabolism and substrate oxidation, such as thyroid hormones (THs), may be important regulators of body weight.
Objective:
We investigated associations of THs cross-sectionally with obesity, energy expenditure, and substrate oxidation and prospectively with weight change.
Design:
Euthyroid, nondiabetic, healthy, adult Pima Indians (n = 89; 47 M, 42 F) were studied. Percentage body fat (%BF) was measured by using dual-energy X-ray absorptiometry; sleeping metabolic rate (SMR), respiratory quotient, and substrate oxidation rates were measured in a respiratory chamber. Thyroid-stimulating hormone (TSH), free thyroxine (T(4)), free triiodothyronine (T(3)), and leptin concentrations were measured in fasting plasma samples.
Results:
TSH, but neither free T(3) nor free T(4), was associated with %BF and leptin concentrations (r = 0.27 and 0.29, respectively; both: P
Conclusions:
In euthyroid Pima Indians, lower free T(3) but not free T(4) concentrations were an independent predictor of SMR and lipid oxidation and a predictor of weight gain. This finding indicates that control of T(4)-to-T(3) conversion may play a role in body weight regulation.
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