Children need calcium to build  bone tissue, but too much calcium can be harmful. Excess blood calcium,  or hypercalcemia, causes the kidneys to work extra hard to remove the  overload. Such high levels lead to the formation of kidney stones. Diet  alone is not always the culprit of high calcium levels.  Sometimes, high  body calcium is caused by genetics, cancer or diseases.
Calcium Requirements
Calcium  is an important mineral that the human body needs to build healthy  bones, form blood clots, contract muscles and help nerves send messages.  It is only available in nature and cannot be created by the body.  Vitamin D assists in calcium absorption. Food is the best source of  calcium, but calcium supplementation offers an alternative. The amount  of calcium needed by the body increases as a child grows. Children 1 to 3  years of age need 500 mg per day, while 9 to 18 year olds need 1,300  mg. Excessive supplementation increases the chance of health problems in  children.
Calcium Supplements
Calcium  supplements contain variable amounts of elemental calcium within  calcium carbonate or calcium citrate. Foods supplemented with other  calcium forms contain gluconate, lactate and phosphate. Fortified juices  contain calcium citrate malate. The amount of calcium absorbed by the  body depends on the amount of elemental calcium consumed. Hypercalcemia  rarely results from dietary or supplemental calcium but tolerable levels  should be measured in elemental calcium.
Relationship to Hormones
The  primary regulators of blood calcium are parathyroid hormone and  calcitonin. As blood calcium levels decrease, the parathyroid glands  produce more parathyroid hormone. The parathyroid hormone stimulates  bones to release calcium, and the digestive tract to absorb more  calcium. As the levels of calcium rise, the thyroid gland produces  calcitonin, which counteracts the calcium release and absorption. The  primary cause of high calcium levels in children is hyperparathyroidism,  or an overactive parathyroid gland. Also, certain medications, such as  lithium and diuretics, may increase the release of parathyroid hormone.
Cancer and Other Diseases
Some  cancerous tumors produce proteins that mimic parathyroid hormone, thus  stimulating calcium release. Also, cancer within bone tissue may cause  increased calcium release. Inflammatory diseases that raise levels of  vitamin D in blood can stimulate excess calcium absorption and a  genetically inherited disease called hypocalciuric hypercalcemia causes  increased blood calcium from faulty calcium receptors. Secondary effects  of diseases causing immobility increase bone calcium release because of  the lack of weight-bearing exercise.
Complications
Untreated  hypercalcemia causes various body system complications. Bones releasing  excess calcium becomes thinner and prone to fractures. Growing children  with hypercalcemia may develop spinal curvature and short stature.  Calcium crystals may accumulate in kidneys and cause kidney stones.  Excessive calcium damages the kidneys' ability to filter blood properly,  resulting in renal disease. Even the nervous and cardiac systems are  affected when showing signs of dementia, confusion and irregular  heartbeats.
Treatment Options
The  first treatment option is hydration. Increasing the fluid flow through  the kidneys will dilute blood calcium, making it less likely to damage  the kidneys. Treatment with diuretics functions in the same way, by  increasing fluid flow through the kidneys. Bisphosphate drugs will  inhibit bone breakdown and adding calcitonin reduces calcium absorption.  Treating high levels of vitamin D with glucocorticoids decreases  calcium absorption as well. If kidneys are impaired, hemodialysis will  remove excess toxins and calcium from the blood. Once blood calcium  levels return to normal, underlying causes must be investigated.
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