Maushart CI, Senn JR, Loeliger RC, et al. - According to this prospective cohort study, in patients with overt hyperthyroidism, cold-induced thermogenesis (CIT) is not elevated.

• Participants in the study were 18 patients with overt hyperthyroidism.

• The levels of free T4 (fT4) and free T3 (fT3) declined significantly with time (fT4, p = 0.0003; fT3, p = 0.0001).

• Resting energy expenditure (REE) corrected for lean body mass (LBM) dropped from 42 ± 6.7 kcal/24h/kg LBM in the hyperthyroid to 33±4.4 kcal/24h/kg LBM in the euthyroid state and 3 months later to 33 ± 5.2 kcal/24h/kg LBM.

• REE was predicted by free T4 and free T3.

• CIT did not go from being hyperthyroid to being euthyroid.

• Hyperthyroidism increased skin temperature in warm environments but had no effect on core body temperature or skin temperature after cold exposure.

• During the hyperthyroid state, REE and CIT had no effect on weight regain or body composition.