- Niacin, also known as vitamin B3, is a water-soluble B-complex vitamin essential for energy metabolism, DNA repair, and overall cellular function.
- It exists in two main forms: nicotinic acid and nicotinamide (niacinamide), both of which are precursors to the coenzymes NAD⁺ (nicotinamide adenine dinucleotide) and NADP⁺ (nicotinamide adenine dinucleotide phosphate). These coenzymes are involved in more than 400 enzymatic reactions in the body, playing critical roles in converting carbohydrates, fats, and proteins into usable energy. Niacin is also vital for maintaining the health of the skin, digestive tract, and nervous system.
- Niacin is unique among vitamins in that it can be synthesized in the human body from the amino acid tryptophan, although this conversion is relatively inefficient and depends on adequate availability of other nutrients such as vitamin B6 and riboflavin. Dietary sources of niacin include poultry, red meat, fish, whole grains, legumes, seeds, and fortified foods. In populations that rely heavily on corn-based diets without proper processing (such as nixtamalization), niacin deficiency can become prevalent because corn contains niacin in a bound form that is not readily bioavailable.
- Severe niacin deficiency leads to pellagra, a disease historically associated with poverty and malnutrition. Pellagra is characterized by the “three Ds”: dermatitis, diarrhea, and dementia. If left untreated, it can progress to a fourth “D”—death. The skin symptoms typically appear as symmetrical, sun-sensitive rashes, while gastrointestinal disturbances include nausea, vomiting, and inflammation of the mouth and tongue. Neurological effects range from irritability and poor concentration to severe cognitive impairment and psychosis.
- In modern clinical settings, niacin is sometimes prescribed in pharmacological doses (far higher than dietary requirements) to treat high cholesterol. Nicotinic acid, in particular, has been shown to significantly raise HDL (good) cholesterol and lower LDL (bad) cholesterol and triglycerides. However, high-dose niacin therapy can cause side effects, the most common of which is flushing—a temporary reddening of the skin due to vasodilation. Other possible side effects include liver toxicity, gastrointestinal issues, increased blood sugar levels, and, in rare cases, muscle damage, especially when combined with statins.
- The recommended daily allowance (RDA) for niacin varies by age, sex, and physiological status but generally ranges from 14 to 16 mg NE (niacin equivalents) per day for adults. One niacin equivalent equals 1 mg of niacin or 60 mg of tryptophan. Because niacin is water-soluble, excess amounts from food are typically excreted in the urine, though sustained high doses from supplements can lead to toxicity.
