Which of the following is a listed cause of hypercalcemia related to vitamin D activity?

• A. Vitamin D deficiency
• B. Vitamin D excess
• C. Thiamine deficiency
• D. Vitamin C excess

Answer: (B)

Excess vitamin D activity raises calcium levels in the blood by increasing how much calcium is absorbed from the gut and by promoting calcium release from bone. When there’s too much active vitamin D, the normal mechanisms that keep calcium in balance get overwhelmed, leading to hypercalcemia. This is why vitamin D excess is a listed cause of hypercalcemia.

In contrast, vitamin D deficiency reduces calcium absorption and tends to cause low calcium levels, not high. Thiamine deficiency and vitamin C excess aren’t driven by vitamin D activity and don’t typically cause hypercalcemia.