A compound X is present in certain vegetables and is necessary for DNA maintenance. Laboratory studies show humans can produce small amounts of X, but not enough when dietary intake is absent, and deficiency causes a disease that resolves when X is added to the diet. According to the definition used in class, how should X be classified?

• A. An essential nutrient because it must be obtained from diet in adequate amounts
• B. A semi-essential or conditionally essential nutrient because endogenous synthesis is insufficient in absence of dietary intake
• C. A phytochemical with no nutritional relevance to human growth and maintenance
• D. A nonessential dietary component because the body can synthesize it in trace amounts under basal conditions

Answer: (A)