Relationship between thyroid hormones, resting energy expenditure and cardiometabolic risk factors in euthyroid subjects

Background & aims: Whereas hypothyroid subjects have a decreased resting energy expenditure (REE), it is unknown whether REE is associated with TSH in euthyroid subjects. It is also uncertain whether there is an association between cardiometabolic risk factors and TSH among euthyroid subjects. The primary aim was to test whether REE and TSH are associated in euthyroid subjects. The second aim was to evaluate the association between TSH and cholesterol, HDL-cholesterol, triglycerides, glucose and blood pressure. Methods: 885 Caucasian euthyroid subjects (75% women) aged 18-79 years and with a median body mass index of 28.6 kg/m2 were consecutively studied at our Research Center. REE was measured using a canopy-equipped indirect calorimeter. Multivariable regression of 25th, 50th and 75th percentiles was used to evaluate the association between the outcomes (REE, cholesterol, HDL-cholesterol, triglycerides, glucose and blood pressure) and the predictors (TSH, FT4 and FT3) controlling by gender, age and body mass index. Results: REE was not associated with TSH, FT4 and FT3 at any percentile. On the contrary, a positive association between TSH and triglycerides was evident at all percentiles. A positive association between FT3 and HDL-cholesterol was also present but only at the 75th percentile. Conclusions: REE is not associated with TSH in euthyroid subjects. It is however positively associated with triglycerides confirming the findings of recent population studies.