What effect does thyroid hormone have on metabolism?

Thyroid hormone plays a pivotal role in regulating metabolism. It primarily acts to accelerate metabolic processes, which is crucial for various physiological functions. This acceleration occurs because thyroid hormones, mainly thyroxine (T4) and triiodothyronine (T3), enhance the basal metabolic rate by increasing the rate of oxygen consumption and heat production in tissues. They promote the metabolism of carbohydrates, fats, and proteins, thus elevating the overall energy expenditure of the body.

Thyroid hormones stimulate metabolic pathways such as glycolysis, gluconeogenesis, lipolysis, and protein synthesis. This stimulation leads to increased levels of key enzymes involved in these pathways, highlighting their significant impact on both the synthesis and breakdown of various substrates in the body.

Because of this direct effect on metabolic processes, the notion that thyroid hormone inhibits, has no effect at all, or merely registers slight decreases in metabolic activity does not hold true. Rather, the correct understanding is that thyroid hormones are essential for proper metabolic functioning and energy homeostasis, making the acceleration of metabolic processes their primary effect.