Which best describes the function of niacin?

• A. Energy metabolism
• B. Calcium regulation
• C. Antioxidant enzyme activity
• D. Collagen synthesis

Answer: (A)

Niacin is essential because it forms the coenzymes NAD+ and NADP+, which act as carriers of electrons in many energy-yielding reactions. These coenzymes are required for redox steps throughout glucose breakdown, the pyruvate dehydrogenase complex, the TCA cycle, and beta-oxidation, ultimately supporting ATP production. NADP+ and NADPH also support biosynthetic processes and antioxidant defenses, but the primary description that fits niacin’s role is its central part in energy metabolism.

Calcium regulation is governed mainly by vitamin D and related hormones, not niacin. Antioxidant enzyme activity is carried out by enzymes like SOD and glutathione peroxidase that rely on reducing equivalents, including NADPH, but niacin’s best-described function is providing those coenzymes for energy metabolism. Collagen synthesis relies on vitamin C for collagen hydroxylation.