Vitamins >> Vitamin B3 Deficiency

Pellagra

The late stage of severe niacin deficiency is known as pellagra. Early records of pellagra followed the widespread cultivation of corn in Europe in the 1700's . The disease was generally associated with the poorer social classes whose chief dietary staple consisted of cereals, like corn or sorghum. Pellagra was also common in the southern United States during the early 1900's where income was low and corn products were a major dietary staple . Interestingly, pellagra was not known in Mexico, where corn was also an important dietary staple and much of the population was also poor. In fact, corn contains appreciable amounts of niacin, but it is present in a bound form that is not nutritionally available to humans. The traditional preparation of corn tortillas in Mexico involves soaking the corn in a lime (calcium oxide) solution, prior to cooking. Heating the corn in an alkaline solution results in the release of bound niacin, increasing its bioavailability.

The most common symptoms of niacin deficiency involve the skin, digestive system, and the nervous system . The symptoms of pellagra were commonly referred to as the four D's: dermatitis, diarrhea, dementia, and death. In the skin, a thick, scaly, darkly pigmented rash develops symmetrically in areas exposed to sunlight. The word "pellagra" comes from the Italian phrase for rough or raw skin. Symptoms related to the digestive system include a bright red tongue, vomiting, and diarrhea. Neurologic symptoms include headache, apathy, fatigue, depression, disorientation, and memory loss. If untreated, pellagra is ultimately fatal.

Nutrient interactions (tryptophan and niacin)

In addition to its synthesis from dietary niacin, NAD may also be synthesized in the liver from the dietary amino acid, tryptophan. The synthesis of niacin from tryptophan also depends on enzymes that require vitamin B₆ and riboflavin, as well as an enzyme containing heme (iron). On average, 1 mg of niacin can be synthesized from the ingestion of 60 mg of tryptophan. Thus, 60 mg of tryptophan are considered to be 1 mg of niacin equivalents (NE). However, studies of pellagra in the southern United States during the early twentieth century indicated that the diets of many individuals who suffered from pellagra contained enough NE to prevent pellagra , challenging the idea that 60 mg of dietary tryptophan are equivalent to 1 mg of niacin. One study, in particular, found that the tryptophan content of the diet had no effect on the decrease in red blood cell niacin content that resulted from decreased dietary niacin in young men.

Causes of niacin deficiency

Niacin deficiency or pellagra may result from inadequate dietary intake of niacin and/or tryptophan. As mentioned above, other nutrient deficiencies may also contribute to the development of niacin deficiency. Patients with Hartnup's disease, a hereditary disorder resulting in defective tryptophan absorption, have developed pellagra . Carcinoid syndrome, a condition of increased secretion of serotonin and other catecholamines by carcinoid tumors, may also result in pellagra due to increased utilization of dietary tryptophan for serotonin rather than niacin synthesis. Prolonged treatment with the anti-tuberculosis drug, Isoniazid, has also resulted in niacin deficiency.

The Recommended Dietary Allowance (RDA)

The RDA for niacin, revised in 1998, was based on the prevention of deficiency. Pellagra can be prevented by about 11 mg NE/day, but 12 mg to16 mg/day has been found to normalize the urinary excretion of niacin metabolites (breakdown products) in healthy young adults. Because pellagra represents severe deficiency, the Food and Nutrition Board (FNB) chose to use the excretion of niacin metabolites as an indicator of niacin nutritional status rather than symptoms of pellagra. However, some researchers feel that cellular NAD and NADP content may be more relevant indicators of niacin nutritional status.

*NE, niacin equivalent: 1 mg NE = 60 mg of tryptophan = 1 mg niacin

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