A child presents with symptoms of vitamin D deficiency. What is the probable serum finding associated with low vitamin D?

• A. Increased serum calcium
• B. Decreased parathyroid hormone
• C. Decreased serum phosphorus
• D. Normal serum calcium

Answer: (C)

When a child presents with symptoms of vitamin D deficiency, one of the notable serum findings is decreased serum phosphorus levels. Vitamin D plays a crucial role in phosphorus metabolism, aiding in its intestinal absorption. Insufficient levels of vitamin D typically lead to impaired absorption of phosphorus, resulting in lower serum phosphate levels.

In vitamin D deficiency, the body may attempt to compensate for low calcium levels, which can lead to secondary hyperparathyroidism. This condition often results in the elevation of parathyroid hormone, which mobilizes calcium from bones but may still not resolve the phosphorus deficiency caused by impaired absorption. Consequently, the overall serum phosphorus level can drop, leading to a deficiency which can subsequently affect bone health and development.

Thus, the statement about decreased serum phosphorus aligns with the physiological impact of vitamin D deficiency, underscoring its importance in maintaining balanced mineral levels in the body.