Upper Intake Limit For Niacin
Chester J. Zelasko, Ph.D. | July 27, 2004

Recently, a national magazine published an article referring to Tolerable Upper Limits (UL) of certain vitamins and minerals. Since then, Better Life Unlimited has been deluged with e-mails and phone calls asking about the safety of dietary supplements that may exceed the UL for niacin. This Newsletter will examine a single nutrient--niacin--and explain what the UL means and doesn't mean.

Niacin is essential for its role as a coenzyme. Simply stated, it carries ions back and forth between molecules to help the body produce energy--that's why niacin is often recommended to increase a person's energy level. It's also used in the production of fatty acids and in DNA replication. Of the several types of niacin, nicotinamide and nicotinic acid are the most common forms. The breakdown of the amino acid tryptophan can also result in the formation of nicotinamide.

The rate at which niacin is absorbed from food depends on the type of food. It's poorly absorbed from cereal grains but readily absorbed from beans and liver and from foods enriched with niacin. However, the UL concerns only the niacin added to fortify foods, as a dietary supplement, or at pharmaceutical strength to treat a disease.

The current Dietary Reference Intake (DRI) for niacin is 14 mg per day for adult women and 16 mg per day for adult men. The UL was set at 35 mg for all adults.

Who set the UL? DRIs and ULs are set by a committee of the Institutes of Medicine in the U.S. National Academy of Sciences. The committee examines the research to find what problems can occur when taking too much of a vitamin or mineral and then determines the lowest observed adverse effect level (LOAEL).

The initial adverse effect of taking too much niacin is a temporary flushing of the skin that may lead to a slight itching. The other effects of excessive niacin intake apply only to pharmaceutical use of niacin to lower cholesterol at amounts that exceed 3 grams (3,000 mg) per day. That wasn't stated in the magazine article.

So what does this mean if your multivitamin or B-complex exceeds the UL--up to 50, 100, or even 200 mg per day? Probably nothing, because there is more to consider. The form of niacin is important. If nicotinamide or niacinamide is used in the supplement, flushing is not as likely to occur as it would with nicotinic acid, based on the DRI recommendations (1). Most supplements use a blend of niacin sources which reduces the probability of flushing.

Bottom line: nutrition is complicated. Setting standards for an entire society requires the most conservative estimates be used to limit any potential adverse effects. The problem is that strategy may limit beneficial nutrients for most people because of potential adverse effects for a very few.

What should you do? That's up to you--discuss it with your healthcare provider or dietician. In this case, because the adverse effect is relatively benign and temporary, you might try the supplement to see how it affects you; if your skin flushes and itches, reduce your intake. While government standards can protect a society, they do not reveal how exceeding the standard will affect a single individual.

Reference:

  1. Standing Committee on the Scientific Evaluation of Dietary Reference Intakes. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. Food and Nutrition Board, Institute of Medicine, NATIONAL ACADEMY PRESS. Washington, D.C. 2000.
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