Not all water-soluble vitamins are strictly required in the diet since the human body has the capacity to synthesize at least one of this class of vitamin. However, the ability to do so is limiting and not of sufficient capacity to provide all the necessary coenzyme required for normal metabolic processes. Which of the following is this vitamin?

Question

Quizplus · Accepted Answer

The human body can synthesize niacin from the amino acid tryptophan, but this synthesis is not sufficient to meet the body's full requirements, so dietary intake is still necessary. Niacin is not a true vitamin in the strictest definition since it can be derived from the amino acid tryptophan. However, the ability to utilize tryptophan for niacin synthesis is insufficient (60 mg of tryptophan are required to synthesize 1 mg of niacin). Also, synthesis of niacin from tryptophan requires vitamins B₁, B₂, and B₆ which would also likely be limiting on a marginal diet.

Not All Water-Soluble Vitamins Are Strictly Required in the Diet