Assertion (A) : The deficiency of Vitamin D causes rickets. Reason (R) : The deficiency of Vitamin D leads to the increased loss of Ca++ in urine.

Assertion (A) is true as vitamin D deficiency is the primary cause of nutritional rickets, a condition characterized by impaired bone mineralization and skeletal deformities [c3][t1][t6]. Vitamin D, specifically its active form calcitriol, is essential for maintaining calcium homeostasis by promoting intestinal calcium absorption and renal reabsorption [t8]. Reason (R) is false because vitamin D deficiency actually leads to decreased calcium absorption, resulting in hypocalcemia. This triggers secondary hyperparathyroidism, where parathyroid hormone (PTH) levels rise to maintain serum calcium by increasing bone resorption and enhancing renal calcium reabsorption while increasing phosphate excretion [t1][t3]. Consequently, in vitamin D deficiency, the body attempts to conserve calcium at the renal level rather than increasing its loss in urine. Hypercalciuria (increased calcium in urine) is typically associated with vitamin D toxicity or hypercalcemia, not rickets-inducing deficiency.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > The effects of smog > p. 65
2. [2] https://www.ncbi.nlm.nih.gov/books/NBK562285/
3. [3] https://pmc.ncbi.nlm.nih.gov/articles/PMC3257679/
4. [4] https://www.sciencedirect.com/science/article/abs/pii/S1521690X15000627