Thyroid hormone triiodothyronine (T3) is found to boost fat accumulation

A double whammy for fat loss

The so-called activated thyroid hormone triiodothyronine (T3) (the metabolite of the relative inactive T4/thyroxine) has been found to boost fat accumulation in fat cells by increasing fatty acid synthase/FAS and at by inhibiting hormone sensitive lipase/HSL the same time.

Thyroid hormone is well-known to help with weight loss, but as this study shows it actually has an anabolic role on fat tissue. This means that thyroid hormone exerts it's slimming effect by boosting metabolism in muscles and organs, not by acting on fat cells directly.



  • Paper: Triiodothyronine enhances accumulation of intracellular lipids in adipocytes through thyroid hormone receptor α via direct and indirect mechanisms.
  • Abstract: Triiodothyronine (T3) enhanced the expression of adipogenic and lipogenic genes with elevation of the intracellular lipids through thyroid hormone receptor (TR) α in mouse 3T3-L1 cells. However, the transcription of the SREBP-1c and HSL genes was decreased by T3. Such T3-mediated alterations were negated by TRα siRNA. Chromatin immunoprecipitation assay showed that the binding of TRα to the TR-responsive element (TRE) of the FAS promoter was elevated by T3. In contrast, the ability of TRα to bind to the TRE of the SREBP-1c promoter was decreased by T3. In addition, the binding of SREBP-1c to the SRE of the HSL promoter was lowered by T3. These results indicate that T3 increased the accumulation of intracellular lipids by enhancing the expression of the FAS gene through direct binding of TRα to the FAS promoter and simultaneously lowered the amount of lipolysis via reduced binding of T3-decreased SREBP-1c to the HSL promoter.