Which statement correctly summarizes the metabolic consequences of thyroid hormones?

Which statement correctly summarizes the metabolic consequences of thyroid hormones?

• A. Increase energy expenditure only.
• B. Decrease basal metabolic rate, heat production, and energy expenditure.
• C. No change in basal metabolic rate, heat production, or energy expenditure.
• D. Increase basal metabolic rate, heat production, and energy expenditure.

Answer: (D)

Thyroid hormones elevate metabolism throughout the body. They raise the basal metabolic rate, increase heat production, and boost overall energy expenditure. This happens because T3 and T4 enhance mitochondrial activity and the enzymes that drive energy production, raise Na+/K+ ATPase activity, and amplify thermogenic responses, including sympathetic stimulation and, in brown adipose tissue, uncoupling processes that release energy as heat. So the statement that basal metabolic rate, heat production, and energy expenditure all increase best captures the metabolic consequences of thyroid hormones. The other options conflict with this broad stimulatory effect: one suggests a decrease, one suggests no change, and one implies only energy expenditure rises while omitting the changes in resting heat production and BMR.