What is the role of brown adipose tissue in adult humans, and how is it activated?

• A. Brown adipose tissue contributes to non-shivering thermogenesis; activated by cold exposure via sympathetic nerves and norepinephrine increasing UCP1 activity
• B. Brown fat stores calories
• C. Brown fat causes shivering
• D. Brown fat only in infants, not adults

Answer: (A)

Brown adipose tissue in adults serves to generate heat without shivering. When you’re exposed to cold, the body’s sympathetic nerves release norepinephrine, which acts on brown fat cells. This triggers a cascade that increases cyclic AMP and activates protein kinase A, promoting the breakdown of fats and providing fuel for heat production. The key step is the action of UCP1 (uncoupling protein 1) in the mitochondria: it uncouples the usual workflow of oxidative phosphorylation from ATP production, causing the energy from the proton gradient to be released as heat instead. This non-shivering thermogenesis helps maintain body temperature in the cold.

In adults, brown fat is present but less abundant than in infancy and is located in regions like the neck and around the shoulders. It can be recruited and activated by cold exposure, which raises energy expenditure and contributes to thermoregulation. Diet and hormonal signals can also influence its activity to a lesser extent.

It’s not a store of calories like white fat, and it doesn’t cause shivering (shivering is muscle-based heat production). Also, brown fat is present in adults, not confined to infancy.