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What is Niacin + Food and Supplement Sources of Niacin and Roles in the Body + Deficiency and Toxicity + Tryptophan Conversion

What is niacin?

Niacin is more commonly recognized as vitamin B3 and is part of the B-complex vitamins. Niacin in its two forms, nicotinic acid and nicotinamide and is active in the body as part of co-enzyme structures that participate in many bodily activities. In addition to niacin’s fundamental role in nutrition, higher levels of niacin can be used therapeutically to lower blood cholesterol levels.


What foods contain niacin and what is the supplemented form?

Niacin is found well distributed throughout most foods. Brewer’s yeast and most fish, pork, beef, poultry, mushrooms, and potatoes offer higher niacin content (see Niacin in Foods Table). Niacin in foods appears to be stable in most forms of cooking and storage while some losses may occur during the boiling of foods as well as during the thaw drip. In these cases some niacin can dissolve into the water that eventually is drained from the food. Both nicotinamide or nicotinic acid are used in formulating nutrition supplements, however nicotinamide is the form typically used as well as in food fortification.

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How much niacin do we need?

The adult RDA is 14 and 16 mg for women and men to prevent deficiency and provide for good status, thus is a minimum intake level. Meanwhile during pregnancy and lactation the recommendation increases for women to 18 and 17 NE respectively. Because niacin is important in energy operations it is more appropriate to express recommendations for more athletic people based on level of additional calories burned during exercise and sport training/competition. Here recommendations 6.6 mg of niacin would be recommended for every 1000 calories expended daily. Thus athletes expending 3000 to 5000 calories daily would have a recommendation of 20 to 35 mg. The DRI Tables provides minimum recommended levels for children and teens.


Where is niacin found in our body?

Niacin in foods is well absorbed from our small intestine and is found in all of our cells. Like riboflavin we can expect to find higher concentrations of niacin in more metabolically active tissue. Said differently, niacin in found in higher levels in tissues with higher energy demands such as the heart, brain, liver, and skeletal muscle.Niacin will be lost from the body mostly as part of our urine.


What does niacin do in the body?

Like riboflavin, niacin imparts coenzyme activity to our cells. In fact, hundreds of chemical reactions depend upon niacin to proceed. Like riboflavin in the form of FAD, niacin in the form of NAD (nicotinamide dinucleotide) is a carrier of electrons from energy pathways to the electron-transport chain during aerobic energy metabolism (see Niacin Function Figure). Niacin is also part of another electron-transferring molecule called NADP (nicotinamide dinucleotide phosphate). NADP also transfers electrons between molecules and is vitally important in making cholesterol and fatty acids.


Can we make niacin in our body?

Some niacin can be made in the body starting with the essential amino acid tryptophan. However, the conversion is very inefficient and it requires about 60 mg of tryptophan to produce 1 mg of niacin. Since daily niacin needs are 13 to 20 mg for adults, it is unrealistic to rely upon the conversion of tryptophan to niacin, especially since tryptophan is not one of the most abundant amino acids in our diet and serves critical roles beyond protein production. Nevertheless, since some niacin can be made from tryptophan, the RDA is stated as niacin equivalents (NE) where 1 NE is equal to 1 mg of niacin or 60 mg of tryptophan.


What happens if too much niacin is consumed?

Ingesting more than 100 mg of niacin as nicotinic acid can result in an uncomfortable feeling. Headache and itching are common accompanied by an increased blood flow to our skin ( “flushing ”). On the other hand, physicians often prescribe niacin (2 to 5 g/day) as a means of reducing blood cholesterol. Because gram doses of niacin can have a pharmaceutical effect, this practice is not suggested unless under medical supervision. Furthermore a Tolerable Upper Limit is set at 35 mg day.


What happens in niacin deficiency?

Based on the many roles of niacin in energy processes poor niacin status can reduce the efficiency of energy systems. Some of the earlier symptoms of a niacin deficiency include a decreased appetite, weight loss, and a general feeling of weakness. More severe niacin deficiency can result in a severe disease syndrome called pellagra which is characterized by the three “D’s” (dermatitis, diarrhea, dementia) possibly leading to the fourth “D” (death). 




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