Provide an example of a nutrient interaction in which one nutrient enhances the absorption or effectiveness of another.

• A. Vitamin C enhances non-heme iron absorption.
• B. Vitamin D enhances calcium absorption.
• C. Vitamin B12 enhances iron absorption.
• D. Calcium enhances magnesium absorption.

Answer: (A)

Think about how a nutrient can change the way another nutrient behaves in the gut. A classic example is vitamin C and non-heme iron. Non-heme iron, found in plant foods, isn’t absorbed very well on its own because it tends to be less soluble after meals. Vitamin C acts as a reducing agent, converting ferric iron (Fe3+) to the more soluble ferrous form (Fe2+). It also forms a soluble complex with iron, helping it stay dissolved at the pH of the intestine and making it easier to take up by the intestinal cells. This combination of keeping iron soluble and enhancing its transport into enterocytes explains why vitamin C boosts non-heme iron absorption, especially from plant-based meals.

For context, other interactions exist—such as vitamin D improving calcium absorption by increasing the intestinal transport of calcium—but the vitamin C and non-heme iron interaction is a straightforward, well-established example of one nutrient directly enhancing the absorption of another.