- A water-soluble vitamin which occurs in three forms, niacin, nicotinic acid and nicotinamide. The first two can cause skin flushing and should only be taken by diabetics and persons with peptic ulcers under strict medical supervision. Both niacin and nicotinamide forms are essential for bodily health. They are widely distributed in foodstuffs. meat, fish, wholemeal flour and peanuts are major sources. maize contains the vitamin in a non-absorbable form and it is for this reason that it is treated with lime which makes the vitamin available as well as improving the taste. Lack of the vitamin causes pellagra summarized as diarrhoea, dermatitis and dementia. It can also cause severe lesions when the skin is exposed to light.