Thyroid Status Inversely Related To Brown Fat Activity

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Specially Haidut's comment on brown fat made it interesting for me Fat Loss Through Topical Thyroid Or Thyroid Injections?

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Presence of brown adipose tissue in an adolescent with severe primary hypothyroidism. - PubMed - NCBI

Context:

Brown adipose tissue (BAT) generates heat during adaptive thermogenesis in response to cold temperature. Thyroid hormone (TH) receptors, type 2 deiodinase, and TSH receptors are present on brown adipocytes, indicating that the thyroid axis regulates BAT. It is unknown whether absent TH in humans would down-regulate development of BAT and its thermogenic function.
Objective:

The objective of the study was to examine BAT by magnetic resonance imaging (MRI) and infrared thermal imaging (IRT) in a pediatric patient with severe primary hypothyroidism before and after TH treatment.
Design/Setting:

This study was a case report with longitudinal follow-up in a tertiary center.
Main Outcome Measures:

BAT fat fraction (FF) by MRI and skin temperature by IRT were measured.
Results:

An 11.5-year-old female was severely hypothyroid (TSH, 989 μIU/mL; free T4, 0.10 ng/dL; low thyroglobulin, 3.0 ng/mL). Low MRI measures of FF (56.1% ± 3.7%) indicated that BAT was abundantly present in the supraclavicular fossa. IRT showed higher supraclavicular temperature (36.0°C ±0.16°C) than the suprasternal area (34.3°C ± 0.19°C). After 2 months of TH replacement, she was euthyroid (TSH, 4.3 μIU/mL; free T4, 1.49 ng/dL; T3, 102 ng/dL) at which time supraclavicular BAT decreased (increased FF 60.7% ± 3.8%). IRT showed a higher, more homogeneous skin temperature throughout the upper thorax (supraclavicular, 37.1°C ± 0.23°C; suprasternal, 36.4°C ± 0.13°C). The overall size of the supraclavicular fat depot decreased from 84.79 cm3 to 41.21 cm3.
Conclusions:

These findings document the presence of BAT and thermogenesis in profound hypothyroidism and suggest a role for TSH and/or TRH as a potential regulator of BAT.

.At diagnosis, our patient presented with very high serum concentrations of TSH, without negative feedback of TH on either TSH or TRH. After TH replacement, TSH normalized, accompanied by substantial decreases in volume of the supraclavicular fat depot and the amount of BAT at this site. These clinical observations raise the possibility that TSH, and possibly TRH, stimulates BAT thermogenesis to protect a further decrease in body temperature in the hypothyroid state