Marc was a participant in a clinical study to determine how much niacin cures pellagra, the niacin deficiency disease. During the study, he consumed only a formula diet that was deficient in niacin. After developing pellagra, he was given 2 mg of niacin a day for 2 weeks, but he still suffered from the disease, so the scientists added 2 mg of the vitamin to Marc's formula. By the beginning of the 5th week of the study, the researchers noticed that Marc's signs and symptoms were greatly improved. At the end of the 5th week, he was feeling fine. The researchers concluded that: