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Hyperthyroidism increased brown fat metabolism
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Hyperthyroidism increased glucose uptake in brown adipose tissue independent of brown adipose tissue perfusion, according to follow-up study results published in the Journal of Clinical Endocrinology and Metabolism.
Researchers wrote that previous reports showed brown adipose tissue metabolism is upregulated by thyroid hormones in rats. Therefore, researchers carried out a study to measure glucose uptake and perfusion of brown adipose tissue, white adipose tissue, skeletal muscle and thyroid glands using PET imaging in 10 human patients with overt hyperthyroidism and eight healthy controls.
Patients with hyperthyroidism displayed a threefold greater amount of brown adipose tissue glucose uptake compared with healthy patients (2.7 mcmol/100 g/min vs. 0.9 mcmol/100 g/min; P=.0013), 90% higher skeletal muscle glucose uptake (P<.005), 45% higher energy expenditure (P<.005) and 70% higher lipid oxidation rate (P=.001), according to data.
However, the changes were reversible after restoration of euthyroidism, researchers wrote. During hyperthyroidism, serum free thyroxine and triiodothyronine were strongly associated with energy expenditure and lipid oxidation rates (P<.001). Thyroid-stimulating hormone had an inverse correlation with brown adipose tissue and skeletal muscle glucose metabolism (P<.001), according to data.
Hyperthyroidism had no effect on brown adipose tissue perfusion. However, it stimulated skeletal muscle perfusion (P=.04), researchers wrote. Thyroid gland glucose uptake did not differ between patients with hyperthyroidism and euthyroidism.
“These metabolic changes are similar to what is seen in response to insulin. During hyperthyroidism, activation of [brown adipose tissue] and skeletal muscle by thyroid hormones and simultaneous [sympathetic nervous system] activation may explain increased energy expenditure and higher use of lipids as energy substrate,” researchers wrote.
Disclosure: The researchers report no relevant financial disclosures.
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