Resting Energy Expenditure and Cold-induced Thermogenesis in Patients With Overt Hyperthyroidism

Abstract

Context Thyroid hormone is crucial for the adaptation to cold. Objective To evaluate the effect of hyperthyroidism on resting energy expenditure (REE), cold-induced thermogenesis (CIT) and changes in body composition and weight. Design Prospective cohort study. Setting Endocrine outpatient clinic at tertiary referral center. Patients Eighteen patients with overt hyperthyroidism. Main Outcome Measures We measured REE during hyperthyroidism, after restoring euthyroid TH levels and after 3 months of normal thyroid function. In fourteen patients energy expenditure (EE) was measured before and after a mild cold exposure of two hours and CIT was the difference between EEcold and EEwarm. Skin temperatures at eight positions were recorded during the study visits. Body composition was assessed by dual X-ray absorption. Results Free T4 (fT4) and free T3 (fT3) decreased significantly over time (fT4, p=0.0003; fT3, p=0.0001). REE corrected for lean body mass (LBM) decreased from 42 ± 6.7 kcal/24h/kg LBM in the hyperthyroid to 33±4.4 kcal/24h/kg LBM (-21%, p<0.0001 vs hyperthyroid) in the euthyroid state and three months later to 33 ± 5.2 kcal/24h/kg LBM (-21%, p=0.0022 vs. hyperthyroid, overall p<0.0001). Free T4 (p=0.0001) and free T3 (p<0.0001) were predictors of REE. CIT did not change from the hyperthyroid to the euthyroid state (p=0.96). Hyperthyroidism led to increased skin temperature at warm ambient conditions but did not alter core body temperature, nor skin temperature after cold exposure. Weight regain and body composition were not influenced by REE and CIT during the hyperthyroid state. Conclusions CIT is not increased in patients with overt hyperthyroidism.

Acute effect of propranolol on resting energy expenditure in hyperthyroid patients

“…It is known, that hyperthyroidism increases core body temperature in rodents ( 20 ). In hyperthyroid humans core body temperature is often markedly elevated in the setting of thyroid storm ( 21 ) but usually normal in clinically stable hyperthyroid outpatients ( 18 ). We wondered whether the acute dose of propranolol affected body temperature.…”

“…The study visits and examinations took place in the morning, after a fasting period of at least 6 hours. The study comprised also an observational part in which the effect of hyperthyroidism on cold-induced thermogenesis (CIT) and body composition were evaluated and which has been published previously ( 18 ).…”

The Role of Thyroid Hormones on Skeletal Muscle Thermogenesis

“…They also observed that the contents of these pumps correlate to plasma thyroid hormone levels and resting EE. In the Maushert et al study, CIT was shown to not increase in overt hyperthyroid patients as the skin temperatures of both hyperthyroid and euthyroid individuals were not different after mild cold exposure [79]. The authors suggest that according to the data collected, the lack of CIT in these patients is due to high resting EE in a hyperthyroid state, making further thermogenesis during cold exposure needless.…”

Influence of propranolol plus methimazole on curative efficacy and thyroid function of patients with hyperthyroidism

“…Hyperthyroidism (HT) is a common endocrine disorder characterized by aberrantly elevated thyroid hormone levels in the body, often manifesting as palpitations, sweating, and increased food intake but weight loss [1][2][3]. According to relevant epidemiological data, HT affects 0.2-1.3% of people in the world's iodine-sufficient areas [4].…”