Overview
Vitamin B3 includes niacin and nicotinamide, precursors of NAD and NADP. These cofactors support energy metabolism, DNA repair, redox balance, and signaling. See Vitamin B3 and B-complex vitamins.
Mechanism
NAD and NADP shuttle electrons and support enzymes such as dehydrogenases, sirtuins, and PARP proteins. Niacin can also activate the G-protein-coupled receptor GPR109A at pharmacologic exposures.
Uses
Niacin prevents pellagra and treats deficiency. Prescription niacin has lipid effects, but modern cardiovascular practice weighs limited outcome benefit against adverse effects and usually favors other therapies.
Dosage
Adult niacin-equivalent reference intake is about 14–16 mg/day. The tolerable upper intake level for supplemental nicotinic acid in adults is commonly 35 mg/day because of flushing; therapeutic doses require prescription supervision and laboratory monitoring.
Adverse effects
Nicotinic acid may cause flushing, itching, headache, gastrointestinal symptoms, elevated glucose, liver injury, and uric-acid elevation. Extended-release products can be particularly hepatotoxic. Do not combine high doses with lipid medicines without medical oversight.
Claims and evidence
Niacin reliably corrects deficiency and changes lipid measurements, but improving a laboratory value does not guarantee fewer cardiovascular events. Over-the-counter products are not equivalent to prescribed formulations.
Research
Research addresses NAD biology, aging, metabolic disease, pellagra prevention, and safer lipid-modifying agents. Clinical relevance of NAD-boosting strategies remains under investigation.