About Calcium
Blood calcium is tightly regulated by the parathyroid glands, kidneys, and vitamin D — and abnormal levels are almost never about how much calcium you eat. High blood calcium (hypercalcemia) is most commonly caused by overactive parathyroid glands or, less commonly, certain cancers; both require prompt medical investigation. Low calcium (hypocalcemia) can point to vitamin D deficiency, kidney disease, or parathyroid insufficiency and can cause muscle cramps, tingling, and in severe cases cardiac arrhythmias.