Which mechanism links CKD with bone health issues?

• A. Decreased calcium absorption due to reduced activation of vitamin D leading to secondary hyperparathyroidism
• B. Increased calcium absorption due to increased vitamin D
• C. No effect on calcium absorption
• D. Bone health is unaffected

Answer: (A)

This question focuses on how chronic kidney disease disrupts mineral metabolism and bone health. In CKD, the kidneys lose the ability to activate vitamin D to its active form, calcitriol. With less calcitriol, the gut absorbs less calcium, so serum calcium tends to drop. The body responds by increasing parathyroid hormone release, causing secondary hyperparathyroidism. The higher PTH level drives bone resorption to raise calcium levels, leading to weakened bones and renal osteodystrophy. Additionally, CKD causes phosphate to accumulate, which further lowers calcium and sustains elevated PTH, worsening bone turnover.

Options suggesting increased calcium absorption, no effect on calcium, or no impact on bone health don’t fit CKD physiology, because impaired vitamin D activation and subsequent secondary hyperparathyroidism directly link kidney disease to bone problems.