Uses in the body: the several forms of B3 - nicotinic acid (also known as niacin) and nicotinamide - assist with the function of the digestive and nervous systems. They play a role in food metabolism and energy release, as well as the formation of red blood cells and healthy skin.

Signs of deficiency: irritability, fatigue, poor memory, headache, dry skin, poor appetite, mouth ulcers, emotional instability, mental changes. Severe deficiency (now rarely seen) leads to a condition known as pellagra, which is characterised by very dry, cracked skin.

Therapeutic uses: dizziness, PMS, tinnitus, arthritis and in the treatment of burns, alcohol addiction, high cholesterol, mental problems and hyperthyroid (this requires medical supervision). Useful for athletes, the elderly and people suffering from stress.

Dietary sources: meat, fish, dairy produce, fish, fortified cereals, wholemeal bread, brewer's yeast, yeast extract, nuts, seeds, soya beans, potatoes, dried fruit, tomatoes, peas.

Dosage:
Recommended daily allowance: 18mg
Typical therapeutic daily dose: 100mg to 500mg
Daily intake shouldn't exceed: 150mg

Cautions: take under supervision if pregnant or breastfeeding. Don't take if suffering from kidney disease or if a child under 12. Intakes of 150mg and above can lead to facial flushing, which is harmless but annoying. Intakes of more than 3,000mg can cause liver problems.

Best taken: in a yeast-free form with breakfast. Usually found in supplements in the form of nicotinamide.