In vitamin D intoxication, a mild hypercalcemia is best explained by which mechanism?

In vitamin D intoxication, a mild hypercalcemia is best explained by which mechanism?

• A. Increased bone resorption
• B. Increased renal calcium excretion
• C. Increased intestinal calcium absorption
• D. Decreased intestinal calcium absorption

Answer: (C)

The main idea is that too much vitamin D boosts how much calcium the gut can absorb. The active form of vitamin D (calcitriol) increases intestinal calcium transport by upregulating enterocyte proteins like TRPV6 and calbindin, so more dietary calcium enters the bloodstream. With vitamin D intoxication, serum calcium rises modestly because this gut absorption is amplified, and PTH is suppressed, so bone resorption isn’t driving the hypercalcemia as much. Increased renal excretion of calcium would tend to lower calcium levels, and decreased intestinal absorption would actually reduce calcium, not raise it. So the mild hypercalcemia is best explained by increased intestinal calcium absorption.

The main idea is that too much vitamin D boosts how much calcium the gut can absorb. The active form of vitamin D (calcitriol) increases intestinal calcium transport by upregulating enterocyte proteins like TRPV6 and calbindin, so more dietary calcium enters the bloodstream. With vitamin D intoxication, serum calcium rises modestly because this gut absorption is amplified, and PTH is suppressed, so bone resorption isn’t driving the hypercalcemia as much. Increased renal excretion of calcium would tend to lower calcium levels, and decreased intestinal absorption would actually reduce calcium, not raise it. So the mild hypercalcemia is best explained by increased intestinal calcium absorption.