Questions: Minerals and Trace Elements in Human Nutrition

Question 1

Which dietary factor enhances the absorption of non-heme iron from plant sources?

• A. Phytic acid from whole grains
• B. Calcium from dairy consumed in the same meal
• C. Vitamin C (ascorbic acid) from fruits or vegetables
• D. Tannins from tea or coffee consumed with the meal

Answer: (C)

Vitamin C reduces ferric iron (Fe³⁺) to ferrous iron (Fe²⁺), the form that intestinal transporters (DMT1) can absorb. It also chelates iron in a way that keeps it soluble in the alkaline intestinal environment. Phytic acid, tannins, and calcium are all inhibitors of non-heme iron absorption — which is why tea with meals and dairy-heavy diets can worsen iron status in people already at risk.

Question 2

Because zinc and selenium support immune function, supplementing these minerals above recommended daily intake will enhance immune response beyond the baseline level.

• T. True
• F. False

Answer: False

Both zinc and selenium follow U-shaped dose-response curves: deficiency impairs immune function, but excess is also immunosuppressive and can be toxic. High-dose selenium supplementation has been associated with increased risk of type 2 diabetes and adverse cardiac outcomes. Zinc toxicity causes nausea, suppresses copper absorption, and paradoxically impairs immune function. Optimal intake is near the recommended level, not above it.

Question 3

What distinguishes macrominerals from trace elements, and why does this classification matter for dietary planning?

Model answer: Macrominerals are required in amounts greater than 100 mg per day (e.g., calcium at ~1000 mg/day, sodium, potassium, magnesium), while trace elements are required in amounts under 100 mg per day (e.g., iron at ~8–18 mg/day, zinc, iodine, selenium). The classification matters because macrominerals often need deliberate dietary emphasis (especially calcium and potassium), while trace element needs are typically met by varied diets — but deficiencies are harder to detect and toxicities can occur at doses not far above requirements.

The distinction is quantitative, not about importance — iodine is needed only in micrograms per day but iodine deficiency is the leading preventable cause of intellectual disability worldwide. The practical relevance is that macrominerals show up on nutrition labels and are tracked in dietary assessment, while trace elements often require specialized testing to identify deficiencies.