A group of 50 adult male humans were in a clinical study to determine how much niacin is toxic. During the first two weeks of the study, members of the group consumed only a formula diet that was nutritionally complete, except it contained 24 mg niacin, which is 1.5 times the RDA for niacin (males). At that point in the study, all members reported feeling fine, and they could function normally. During the next week, they were given a formula that contained 48 mg niacin. Within a few days of consuming this formula, 90% of the participants reported feeling ill, and they complained of having upset stomachs and reddened facial skin. At that point, researchers gave the subjects a formula that contain 16 mg niacin. After a week of consuming the new formula, all participants reported feeling well again. Based on this information, the researchers concluded that the

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The study showed that consuming 48 mg niacin caused symptoms of toxicity in 90% of the participants, while reducing the intake to 16 mg niacin resulted in symptom resolution. Based on this, the researchers concluded that the UL (tolerable upper intake level) for niacin is between 24 and 48 mg/day. This means that consuming more than 24 mg/day could increase the risk of toxicity, while exceeding 48 mg/day could cause adverse effects for most people.

A Group of 50 Adult Male Humans Were in a Clinical