Nicotinic acid and nicotinamide are generally termed as niacin. Niacin, however, has a special relationship with the essential amino acid tryptophan in that it can act as a precursor of the vitamin in mammalian tissues. Both energy and protein intakes regulate the efficiency of conversion of tryptophan to niacin and it is generally accepted that in well nourished normal individuals 60 mg of tryptophan should be considered as equivalent to 1 mg of niacin. The allowances (mg/day) for various age groups are as follows: