The bioavailability for humans of bound niacin from wheat bran

Ethanolic wheat bran extracts were dialyzed and dried on starch. One portion [bound niacin (BN)] was cooked in steam; another [alkali-treated bound niacin (ABN)] was made alkaline with calcium oxide and then cooked. The niacin in BN was bound to large molecules (gel filtration); in ABN it was free. Three subjects each consumed a standard daily diet containing approximately 20 mg niacin equivalents. Urine was collected throughout. From day 14, each received three doses in random order at 8-day intervals. The doses, each spread over 2 days, were of BN and ABN, containing 35 mg niacin and 24 mg pure nicotinic acid. The above base-line response in urinary metabolites (N1-methylnicotinamide + N1-methyl-2-pyridone-5-carboxamide) over the 6 days from the beginning of each dose was equivalent to 24% of ingested niacin after BN, 62% after ABN and 89% after nicotinic acid. The niacin in BN appeared mostly unavailable.