Why does triiodothyronine affect metabolism and body temperature?

Triiodothyronine (T3) is a biologically active hormone containing iodine that plays a central role in regulating metabolism and body temperature by influencing cellular activity.12

Once inside a cell, triiodothyronine enters the nucleus and binds to receptors, which alters the transcription of specific DNA sequences. This process increases the production of various enzymes and proteins that regulate how cells utilize nutrients and consume oxygen.21

Specifically, triiodothyronine affects energy balance through the mitochondria, the sites where cells produce adenosine triphosphate (ATP) or dissipate energy as heat. By activating substances that increase the proportion of energy released as heat, the hormone directly influences body temperature. Additionally, it stimulates carbohydrate utilization and lipid metabolism, further driving the body's metabolic rate. Through these mechanisms, triiodothyronine ensures that cells maintain the necessary energy levels and thermal regulation required for normal physiological function.12