Which of the following is a consequence of decreased vitamin D binding to VDRs?

• A. Decreased lipid levels
• B. Reduced bone density
• C. Improved muscle strength
• D. Hyperparathyroidism

Answer: (D)

When vitamin D binds to its receptor, it activates genes that boost intestinal calcium absorption, support bone mineralization, and help keep serum calcium balanced. If binding to the receptor is reduced, calcium absorption from the gut falls and serum calcium can drop. In response, the parathyroid glands release more parathyroid hormone to raise calcium levels. This rise in PTH is called secondary hyperparathyroidism, and it drives bone resorption to restore calcium, which over time can lead to lower bone density. So, decreased vitamin D receptor signaling mainly hooks to increased PTH secretion, i.e., hyperparathyroidism, rather than the other options.