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Niacin or B3

   Niacin exists in two forms, nicotinic acid and nicotinamide. Both forms are readily

absorbed from the stomach and the small intestine.

   Niacin is stored in small amounts in the liver and transported to tissues, where it is

converted to coenzyme forms. Any excess is excreted in urine.

   Niacin is one of the most stable of the B vitamins. It is resistant to heat and light, and to

 both acid and alkali environments.

  The human body is capable of converting the amino acid tryptophan  to niacin when

needed. However, when both tryptophan and niacin are deficient, tryptophan is used for

protein synthesis.

Physiological and biochemical functions:

   Niacin takes part in the metabolism of carbohydrates, proteins, and fats through

enzymatic reactions.

   Nicotinamide is a component of two co-enzymes NAD and NADP which take part in

several enzyme reactions like, dehydrogenation reaction in kreb’s cycle, synthesis of fatty

acid and cholesterol etc.

   Nicotinic acid is essential for the normal functioning of the skin, energy metabolism,

 proper digestion and healthy nervous system. It is also important for the conversion of

food to energy.  In nicotinic acid deficiency, lesions of the skin, intestines and nervous

system develop.

Effects of deficiency

  In mild deficiency state weakness, loss of weight, loss of appetite, lassitude,

irritability, burning tongue and constipation occur.

  Pellagra is the characteristic disease resulting from niacin deficiency.

  Pellagra is otherwise known as 3 ‘D’s disease i.e., Dermatitis, Diarrhoea and

Dementia

Dermatitis

  Occurs mainly on the exposed portions of the body to the sunlight

  Reddish, dark brown lesions are seen on the face, neck, surfaces of hands, elbows, feet

  Skin lesions are symmetrical in shape and always occur on both sides of the body

simultaneously

  Cracked and scaly skin

  Burning sensation and itching

  Mucous membrane of the alimentary canal is affected

  Glossitis, abdomen pain, loss of appetite, nausea, vomiting

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Diarrhoea

  The diarrhea may range from a few to several loose stools a day with blood and mucus.

Dementia

  Delirium is the commonest severe mental disturbance in acute pellagra.

  Dementia is more frequently seen in the chronic cases.

  Milder mental disturbances consisting of irritability, change in disposition, depression,

inability to concentrate and poor memory are more common in the mild cases.

  The symptoms of postero-lateral tract of spinal cord degeneration, ataxia(loss of full

control of bodily movements), spasticity  (altered skeletal muscle performance in muscle

tone) and the involvement of the bladder and rectal sphincters are seen in chronic cases.

Dietary sources:

The important sources of niacin in the average diets are cereals, pulses, meat, fish, milk, eggs,nuts and oilseeds.

  The richest natural sources  of niacin are dried yeast, rice polishings, liver and

groundnut.

  Whole cereals, legumes, meat and fish are good sources. 

  Milled cereals, milk, eggs and vegetables are fair sources. 

Requirements:

Tryptophan present in dietary proteins is converted into niacin in the tissues, a

consideration of niacin requirements should also include the niacin provided by the tryptophan in

addition to free niacin present in the diet.

Specific recommendations depend on age, gender, and other factors (such as pregnancy).

Women who are pregnant or producing breast milk (lactating) need higher amounts.

The Food and Nutrition Board at the Institute of Medicine recommends the following dietary

intake for niacin:

Infants

  0 - 6 months: 2 milligrams per day (mg/day)

  7 - 12 months: 4 mg/day

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Children

  1 - 3 years: 6 mg/day

  4 - 8 years: 8 mg/day

  9 - 13 years: 12 mg/day

Adolescents and Adults

  Males age 14 and older: 16 mg/day

  Females age 14 and older: 14 mg/day

TOXIC EFFECTS:

Large doses of niacin can cause liver damage, peptic ulcers, and skin rashes. Even normal doses

can be associated with skin flushing. It can be prescribed as a treatment for elevated total

cholesterol and other types of lipid disorders, but it should only be used with medical supervisiondue to its potential for severe side effects.