Niacin (nicotinic acid)
Niacin is required for the release of energy from food (it is the precursor to the coezymes NAD and NADP which are fundamental to key reactions in carbohydrate metabolism). As a result niacin requirement is related to the amount of energy consumed. Niacin is also required for the normal function of the skin and mucous membranes and for normal functioning of the nervous system.
Niacin can be synthesised from the essential amino acid tryptophan to meet daily requirements and dietary intake is only necessary when tryptophan metabolism is disturbed or intake of this amino acid is inadequate.
Deficiency of niacin results in the disease pellagra. It is characterized by sun-sensitive skin producing effects similar to severe sunburn. Advanced pellagra also results in dementia and if untreated is fatal. Pellagra is now rare but was a major public health problem in the early part of the last century up until the 1980s in some parts of the world. It was usually seen in communities where maize forms the staple diet as maize contains little tryptophan and the niacin that is present is in an unavailable form.
Reports of niacin/nicotinic acid toxicity in humans have been observed from its use as a treatment of hyperlipidaemia (high blood lipid levels). Adverse effects are dose related and generally subside with a reduction in dose or the cessation of treatment. Acute toxic symptoms include flushing, itching of the skin, nausea and gastrointestinal disturbances.
Meat, wheat and maize flour, eggs, dairy products and yeast are all dietary sources of niacin.