Which concise statement best distinguishes a true vitamin from a vitamin-like (conditionally essential) nutrient?

• A. True vitamins are organic micronutrients that the body can synthesize reliably under all physiological states and therefore never need to be eaten; vitamin-like nutrients are always obtained exclusively from foods and must be eaten daily to avoid deficiency and organ failure.
• B. True vitamins are macronutrients providing calories and structural substrates that must be eaten for energy under all circumstances, whereas vitamin-like nutrients are only used in signaling and are irrelevant to metabolism except under starvation.
• C. True vitamins are required from the diet under all circumstances; vitamin-like nutrients are usually synthesized endogenously and only required from the diet under special conditions.
• D. True vitamins are inorganic mineral elements required for enzyme function and cannot be synthesized, while vitamin-like nutrients are synthetic pharmaceuticals that mimic vitamin action and are required only in therapeutic contexts.

Answer: (C)