Thyroid Hormone Activates Brown Adipose Tissue and Increases Non-Shivering Thermogenesis--A Cohort Study in a Group of Thyroid Carcinoma Patients.
Level 3 - non-randomized controlled study
Prospective within-subject non-randomized longitudinal cohort study
PubMed 26784028 · doi:10.1371/journal.pone.0145049
What was done
Ten patients with well-differentiated thyroid carcinoma undergoing surgical resection and radioactive iodine ablation were evaluated in a longitudinal cohort study over 6 months. Patients were measured in two states: an overt hypothyroid state following thyroidectomy, and a subclinical hyperthyroid state achieved via TSH-suppressive doses of synthetic levothyroxine. Measured outcomes included basal metabolic rate (BMR), non-shivering thermogenesis (NST), and brown adipose tissue (BAT) activity assessed by standard uptake value (SUVMean), analyzed using paired two-tailed t-tests and linear regression.
What was found
Synthetic thyroid hormone treatment significantly increased energy expenditure and BAT activation compared to the hypothyroid state. BMR was significantly higher with levothyroxine than in the hypothyroid state (4.4 ± 0.6 kJ/min versus 3.8 ± 0.5 kJ/min, P = 0.012). Non-shivering thermogenesis increased from 15 ± 10% to 25 ± 6% (P = 0.009). Mean BAT activity (SUVMean) was higher in the subclinical hyperthyroid state than in the hypothyroid state (4.0 ± 2.9 versus 2.4 ± 1.8, P = 0.039).
Why it matters
This study provides human in vivo evidence that thyroid hormone levels directly regulate brown adipose tissue activity and cold-activated non-shivering thermogenesis.
Limits
The sample size is very small (n = 10), limiting statistical power and generalizability. The study lacked a non-cancer control group, was non-randomized, and examined extreme hormonal shifts between post-surgical hypothyroidism and TSH-suppressive subclinical hyperthyroidism rather than normal physiological variations.
Cited by
- contradicts Non-shivering thermogenesis can produce a 300% to 500% increase in metabolic rate.