A large body of evidence has accumulated that treatment with riboflavin in excess of nutritional requirements has very little toxicity either for experimental animals or for humans (Rivlin, 1978). There are no reports of riboflavin toxicity studies in swine. Most data from rats suggest that dietary levels between 10 and 20 times the requirement (possibly 100 times) can be tolerated safely (NRC, 1998). Campbell and Combs (1990) fed diets containing up to 0.7% supplemental riboflavin to growing and finishing pigs and observed no effect on performance. When massive amounts of riboflavin are administered orally, only a small fraction of the dose is absorbed, the remainder being excreted in the feces. Lack of toxicity is probably due to the fact that the transport system necessary for the absorption of riboflavin across the gastrointestinal mucosa becomes saturated, limiting riboflavin absorption (Christensen, 1973). Also, capacity of the tissues to store riboflavin and its coenzyme derivatives appears to be limited when excessive amounts are administered.
