Hypercalciuria, or high urine calcium, occurs when the mechanisms for calcium reabsorption in the kidneys are disrupted. Vitamin D facilitates the balance of calcium in the blood but excess vitamin D activity may result in increased urine calcium. Conditions that result in hypercalciuria in relation to vitamin D include hereditary hypophosphatemic rickets with hypercalciuria, familial hypercalciuria and hypoparathyroidism therapy.
Vitamin D and Blood Calcium Regulation
Most of the calcium in the body is contained in bones and only a small fraction circulates in the blood. Blood calcium is regulated by the thyroid gland, parathyroid glands and vitamin D. When blood calcium is low, the parathyroid glands produce parathyroid hormone, which breaks down bone to release calcium into the blood; vitamin D also helps increase blood calcium by facilitating calcium absorption in the intestines. When blood calcium is high, the thyroid glands produce calcitonin, which removes calcium from the blood. Calcium excretion through the kidneys is also regulated by parathyroid hormone; low parathyroid hormone results in increased calcium excretion.
Hereditary Hypophosphatemic Rickets
Hereditary hypophosphatemic rickets is a rare genetic disease involving a dysfunction of the kidneys that results in the increased loss of phosphates in the urine; low phosphates in the blood inhibits parathyroid hormone secretion, which results in hypercalciuria. Vitamin D production increases as well to counteract the loss of calcium in the urine.
Familial Hypercalciuria
Familial hypercalciuria is an inherited disease that results from the increased activity of vitamin D in the intestines; as a result, calcium is absorbed in excess, leading to high blood calcium. High blood calcium in turn inhibits parathyroid hormone secretion and results in hypercalciuria. According to a 1993 study published by the "Journal of Clinical Investigation," the increased activity of vitamin D in familial hypercalciuria is likely due to an increased amount of vitamin D receptors in the intestines.
Hypoparathyroidism Therapy
Hypoparathyroidism results when the parathyroid gland produces insufficient amounts of parathyroid hormone. Hypercalciuria may result as a consequence of treating a person with hypoparathyroidism. According to the "Manual of Endocrinology and Metabolism," hypercalciuria is observed at higher doses of dihydrotachysterol -- a synthetic form of vitamin D used in treating hypoparathyroidism.
References
- "Principles and Practice of Endocrinology and Metabolism"; Calcium and Bone Metabolism; Kenneth L. Becker; 2001
- "The Journal of Clinical Investigation"; Increased Intestinal Vitamin D Receptor in Genetic Hypercalciuric Rats; X Q Li et. al.; 1993
- Manual of Endocrinology and Metabolism"; Disorders of Calciotropic Hormones in Adults; Norman Larvin; 2009
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