In terms of energy use, what do thyroid hormones primarily increase?

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

Answer: (C)

Thyroid hormones raise how much energy the body uses at rest and overall. T3 and T4 boost metabolic processes by increasing the transcription of genes involved in energy production, enhancing mitochondrial activity, and stimulating enzymes such as Na+/K+-ATPase. This leads to higher oxygen consumption and more heat being produced, which is the calorigenic effect. Because energy expenditure includes basal metabolic rate plus heat production and activity-related costs, thyroid hormones elevate all of these components. That’s why the best answer is the one that states increases basal metabolic rate, heat production, and energy expenditure. The other options either imply a decrease, only a partial effect, or no change, which doesn’t fit the broad metabolic stimulation caused by thyroid hormones.