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 fact that 90% of the participants reported feeling ill after consuming 48 mg of niacin suggests that this amount is close to the upper intake level (UL) for niacin, which is the maximum daily intake that is unlikely to cause adverse health effects. Additionally, the fact that all participants felt well again after consuming a formula with 16 mg of niacin suggests that this amount was sufficient to meet their needs, and therefore, the human requirement for niacin is likely lower than 48 mg/day. Therefore, the best choice is D, UL for niacin was between 24 and 48 mg/day.

A Group of 50 Adult Male Humans Were in a Clinical