Fundamentals of Human Nutrition/Niacin

< Fundamentals of Human Nutrition

8.3 NiacinEdit

Niacin, also known as Vitamin B3, is one of the eight, water-soluble B vitamins that is involved in the metabolism of glucose, fat, and alcohol to produce energy. Niacin serves this role as an intermediate of nicotinamide adenine dinucleotide (NAD), and the phosphate form of NAD, NADP; these compounds function in helping oxidation-reduction reactions occur in the body (Higdon 2013).

8.3.1 SourcesEdit

Food sources of niacin include:





-Whole-grain and enriched breads and cereals




-Instead of dietary niacin, the human body is also able to convert dietary tryptophan into niacin. In this case, 60 mg of tryptophan is equal to 1 mg of niacin (Meštrović, 2014).

In terms of supplements, niacin exists as nicotinamide or nicotinic acid. Reasons to take niacin supplements would be to better control cholesterol levels, as well as reduce cardiovascular risks.

8.3.2 FunctionsEdit

Niacin functions as an intermediate for nicotinamide adenine dinucleotide (NAD) and a phosphate form of NAD, NADP. These coenzymes are required by hundreds of enzymes in the body to move electrons and help undergo oxidation-reduction reactions. These redox reactions are involved in catabolizing glucose, fat, and alcohol to ultimately produce energy (Higdon, 2013). In general, B-vitamins help maintain a healthy liver, skin, hair, eyes, and a properly working nervous system. Also, niacin aids in increasing amounts of HDL (high-density lipoproteins), in the body; this augmentation helps in lowering levels of bad, LDL (low-density lipoproteins) in the bloodstream (Ehrlich, 2015). This is especially important in reducing risks of coronary heart disease.

8.3.3 RequirementsEdit

Niacin (vitamin B₃) deficiency is generally uncommon in developed countries, but tends to reside in the homeless or impoverished populations. These populations tend to have poor diet and high alcohol consumption, which impact niacin absorption.[1] Many processed foods, such as bread and cereal, found in the United States are fortified with niacin as well as other B-vitamins to prevent dietary inadequacies. If niacin is not available, tryptophan can be synthesized in small amounts to produce niacin for the body.[2]

Inadequate niacin and/or tryptophan dietary intake can create a dietary deficiency. General causes of inadequate levels of B₃ include diarrhea, alcoholism, obesity, eating disorders, and malnutrition. Niacin deficiency typically accompanies other B-vitamin deficiencies, such as B₆ or B₁₂. This makes it difficult to determine the exact cause of symptoms and thus makes it more difficult to treat. Inadequate intake of niacin is more common among those with corn-based diets. This is because the niacin present in corn is not available for humans to utilize unless it is alkalized first. People who live in Mexico generally do not have issues with niacin deficiency because corn tortillas, which are treated with alkali (soaked), are a dietary staple. Once the corn tortillas are treated with alkali, the niacin becomes biologically available to humans. Corn proteins are also very low in tryptophan thus increasing the risk of niacin deficiency.[3]

The symptoms of B₃ deficiency range in severity, but generally impact the stomach and skin first. The disease associated with severe niacin deficiency is called Pellagra and is characterized by the three D’s: dermatitis, diarrhea, and dementia. Pellagra changes the texture and appearance of skin and causes lesions to develop. Skin may become cracked, scaly, and sometimes darkened if exposed to the sun. Skin conditions may or may not appear in conjunction with other symptoms, or even at all. The gastrointestinal tract can also be impacted by a lack of niacin.[4] Primarily, Pellagra causes stomach pain, nausea, and diarrhea. Pain in the mouth can also result and may even lead to a swollen and reddened tongue. Low levels of B₃ can impact the nervous system if left untreated. Problems such as dizziness, headaches, anxiety, depression, and Dementia (which is mental degradation) can result. If these problems persist and are not supplemented with niacin and/or tryptophan, death could be the ultimate result. Treatment of mild niacin deficiency usually just entails regular doses of niacin, within the RDA (see section 8.3.3). Severe deficiency, called Pellagra, is often treated with nicotinamide. Nicotinamide is used because it can be taken in higher doses without the risk of niacin toxicity (see section 8.3.5). Niacin deficiencies are usually treating with a multi-complex B-vitamin. This is done to help treat deficiencies in all of the B-vitamins, which commonly accompany B₃ deficiency.[5]

8.3.5 ToxicityEdit

The intake of too much niacin could result in a niacin flush, which leads to the dilation of the capillaries and could be painful. Symptoms may include: painful flush and rash, itching, nausea, excessive sweating, blurred vision, liver damage, and impaired glucose tolerance. If taken in large doses, hepatotoxicity may occur, which is where liver cells are damaged. Jaundice has also been known to be a result in too much niacin. Dry skin, skin rashes, low blood pressure, and headaches are also common occurrences when niacin is taken in large amounts. Other than hepatotoxicity, extremely large amounts of niacin in the body can cause gout, an irregular heartbeat, and ulcers in the digestive tract (Higdon, 2013). Also, a study found that those who consume high levels of niacin are twice as susceptible to a stroke. With all these side effects and risks, the upper level of 35 mg of niacin each day is recommended; not surpassing this amount is likely to result in no health risks.


  1. Mestrovic, T. (2010, August 16). Niacin Deficiency. Retrieved September 26, 2015, from
  2. Johnson, L. (2014, October 1). Niacin - Nutritional Disorders. Retrieved September 26, 2015.
  3. Higdon, J. (2000). Micronutrient Information Center: Niacin. Retrieved September 26, 2015, from
  4. Seal, A. (2007). The American Journal of Clinical Nutrition. Retrieved September 26, 2015, from
  5. Ehrlich, S. (2015, August 6). Vitamin B3 (Niacin). Retrieved September 26, 2015, from

Ehrlich, S. (August 6, 2015). Vitamin B3 (Niacin). Retrieved from (Links to an external site.)

Higdon, J., Drake, V., Delage, B., Jacobson, E. (July 2013). Niacin. Retrieved from (Links to an external site.)

Meštrović, T. (November 17, 2014). Niacin Food Sources. Retrieved from (Links to an external site.)