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American Journal of Clinical Nutrition, Vol. 85, No. 2, 440-445, February 2007
© 2007 American Society for Nutrition

ORIGINAL RESEARCH COMMUNICATION

Plasma concentrations of free triiodothyronine predict weight change in euthyroid persons1,2,3,4

Emilio Ortega, Nicola Pannacciulli, Clifton Bogardus and Jonathan Krakoff

1 From the Obesity and Diabetes Clinical Research Section, Phoenix 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

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 (T4), free triiodothyronine (T3), and leptin concentrations were measured in fasting plasma samples.

Results: TSH, but neither free T3 nor free T4, was associated with %BF and leptin concentrations (r = 0.27 and 0.29, respectively; both: P ≤ 0.01). In multiple regression analyses adjusted for age, sex, fat mass, and fat-free mass, free T3 was a positive predictor of SMR (P = 0.02). After adjustment for age, sex, %BF, and energy balance, free T3 was a negative predictor of 24-h respiratory quotient (P < 0.05) and a positive predictor of 24-h lipid oxidation rate (P = 0.006). Prospectively, after an average follow-up of 4 ± 2 y, the mean increase in weight was 3 ± 9 kg. Baseline T3 concentrations were associated with absolute and annual percentage of changes in weight (r = –0.27, P = 0.02, and r = –0.28, P = 0.009, for the age- and sex-adjusted associations, respectively).

Conclusions: In euthyroid Pima Indians, lower free T3 but not free T4 concentrations were an independent predictor of SMR and lipid oxidation and a predictor of weight gain. This finding indicates that control of T4-to-T3 conversion may play a role in body weight regulation.

Key Words: Thyroid hormones • energy expenditure • lipid oxidation • obesity • respiratory chamber






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