Vitamin B3 is one of the eight essential B complex vitamins. It is also known as niacin. It encompasses two pyridine derivatives, nicotinic acid and nicotinamide. These are both heat and stable to acid and alkali and can withstand enzymatic hydrolysis. Niacin in humans is synthesized from tryptophan extracted from dietary sources. As such disruptions in tryptophan metabolism or low consumption can result in niacin deficiency. Additionally, the conversion of tryptophan to niacin is dependent on an enzyme known as kynureninase which is a vitamin B6 dependent enzyme. Therefore, vitamin B6 deficiency can also cause niacin deficiency. Nicotimide is the active form of niacin. It participates in various metabolic processes courtesy of its two main substrates NAD and NADP that are involved in oxidation-reduction reactions.
Niacin is essential in the maintenance of a healthy cardiovascular system. It helps balance the blood cholesterol and tricyglyceride levels. Niacin is used to lower the elevated levels of low density cholesterol (LDL) and boost the levels of high density cholesterol (HDL). This is significant in vascular health as it helps prevent the hardening of arteries. Besides, niacin is involved in the production of histamine that has the ability to dilate blood vessels and hence improve circulation. Unfortunately, niacin has also been shown to increase the levels of homocysteine in blood that may impair with normal cardiac function.
Niacin forms part of coenzymes for instance, nicotinamide is a component of two coenzymes Nicotinamide Adenine Dinucleotide ( NAD) and Nicotinamide Adenine Dinucleotide Phosphate(NADP). These two play significant metabolic roles in living cells. Through these coenzymes, niacin is involved in various biological oxidation-reduction reactions that are essential to electron transport and other cellular respiratory reactions. Specifically, NAD functions as an electron carrier for intracellular respiration to facilitate energy production.
Niacin is also involved in the metabolism of fats, proteins carbohydrates and alcohol as a cofactor to produce energy. On the other hand, NADP functions as a hydrogen donor in processes involving reductive biosynthesis such as fatty acid and steroid synthesis. Also, the niacin derived coenzymes NAD and NADP function as soluble electron carriers between proteins. Therefore, niacin is important for the conversion of food to energy. In addition, NAD molecules are not only essential for energy production and storage but also synthesis of DNA in cells. As such, it enables the normal growth and development especially in growing children.
Aside from energy production, niacin plays a significant role in curbing inflammation. As such, it can be used to reduce inflammatory signs such edema, swelling, redness. Its anti-inflammatory property is also useful in relieving joint pain and swelling. Niacin also enhances muscle strength. Anti-inflammation function also helps niacin maintain a healthy skin. It is responsible for the repair of damaged DNA in exposed areas of the skin that have been damaged by ultra-violet light. Areas of the skin especially exposed areas develop sunburns which then advance to pigmentation and ulceration. The most affected body parts are the neck, forearms and fingers. Additionally, its function as a vasodilator also helps improve blood flow in the skin. This is also crucial for proper brain function since it improves blood flow to the brain.
Typically, the intake of niacin is dependent on the levels of tryptophan in the diet. Niacin deficiency affects the skin, gastrointestinal and nervous system. This is characterized by dermatitis, diarrhea and dementia. The diarrhea is as a result of the inflammation of the mucous membranes in the gastrointestinal tract. Good dietary sources of niacin include whole grains, legumes, peanuts, liver, fish and meat. Milk and egg, although poor sources of niacin are rich in tryptophan.