Vitamin B3 (Niacin). Vitamin B1 (Thiamine). Vitamin B2 (Riboflavin). Vitamin B7 (Biotin). Niacin is the only B vitamin that can be synthesized in the liver from the amino acid tryptophan — on average, 1 mg of niacin can be synthesized from the ingestion of 60 mg of tryptophan.