Vitamin B3, also known as Niacin is the generic term for nicotinic acid and its amide derivative nicotinamide that also exhibits the nutritional activity of nicotinic acid and to which nicotinic acid is converted. Nicotinic acid is a vasodilator and produced flushing which is accompanied by a sensation of itching and burning. When given in large doses, this vitamin produces lower plasma cholesterol and is sometimes used for this purpose although it may cause peptic ulcer disease. Nicotinamide does not possess these properties and is heat stable. These compounds are excreted in the urine.
- Animal sources: Kidney and liver are the richest sources of this vitamin along with meat, fish, egg, milk, tea, and coffee.
- Plant sources: these include whole wheat, dried legumes, unpolished rice, peanuts, leafy vegetables, and tomatoes.
In the body, niacin can be derived from tryptophan 60 mg of tryptophan provides 1 mg of this vitamin B2. In many kinds of cereal such as maize especially, niacin occurs in a bound form which is unavailable to the consumer.
- Niacin is an important vitamin for the metabolism of nutrients such as carbohydrates, fats as well as protein.
- Vitamin B3 is necessary for the performance of normal functions of the skin, intestine and the nervous system.
- This vitamin differs from its other B group vitamin in that an essential amino acid, the tryptophan serves as a precursor.
- Another feature of niacin is that it is not excreted via the urine as such but it is metabolized to at least two major methylated derivatives which are
- N-methyl pyridines.
- Nicotinamide is the part of the structure of the two important coenzymes NAD+ and NADP+ which play important role in biological oxidation.
Vitamin B3 deficiency results in pellagra in humans. This disease is characterized by 3D’s namely diarrhea, dermatitis, and dementia; the fourth D signifying death should also be kept in mind as a severe form of this disease may prove fatal. It is endemic in those areas where maize is the main diet and intake of good quality protein is low. This disease is mostly found in women of childbearing age and in growing children.
Following body organ system are affected due to pellagra.
There are dermatitis, pigmentation, and thickening of the skin. Skin lesions are symmetric and tend to be localized in overexposed areas due to photosensitivity. Pigmentation is specially marked over malar and supraorbital regions. An erythematous eruption resembling sunburn first appears on the back of the hands followed by other regions exposed to the sunlight.
There are inflammation and smooth atrophy of the mucosa of the tongue and mouth showing fissures along with stomatitis, glossitis, and pain on swallowing, anorexia, diarrhea, and proctitis are observed.
This system is involved lately. There occurs myelin degeneration in various regions of the spinal cord and cerebrum which leads to parenthesis and anesthesia. Mental disorders such as general nervousness, confusion, depression, insomnia, delusions, hallucinations, and dementia are seen and these symptoms are may be due to a decreased formation of serotonin from tryptophan. Pellagra is the most serious deficiency disease met within the United States.
Large doses of niacin have been found to result in effects produced by histamine released in large amounts such as flushing, pruritus, aggravation of asthma and gut disturbances. Acanthosis nigricans, a skin condition may also occur. It may lead to even hyperuricemia, hyperglycemia and hepatic toxicity.
The daily requirement of this vitamin is 6.6 mg/1000Kcal of energy intake.