Calcium is an essential mineral. It is the most abundant mineral in the body, is found in some foods, added to others, is available as a dietary supplement, and present in some medicines (such as antacids). Calcium is required for vascular contraction and vasodilation, muscle function, nerve transmission, intracellular signaling and hormonal secretion, though less than 1% of total body calcium is needed to support these critical metabolic functions. Serum calcium is very tightly regulated and does not fluctuate with changes in dietary intakes; the body uses bone tissue as a reservoir for, and source of calcium, to maintain constant concentrations of calcium in blood, muscle, and intercellular fluids.
Dietary calcium is generally safe, but more isn't necessarily better, and excessive calcium doesn't provide extra bone protection.
If you take calcium supplements and eat calcium-fortified foods, you may be getting more calcium than you realize. Check food and supplement labels to monitor how much total calcium you're getting a day and whether you're achieving the RDA but not exceeding the recommended upper limit. Be sure to tell your doctor if you're taking calcium supplements.
For more information on the Mayo Clinic's recommendation about calcium supplementation, check Calcium and calcium supplements: Achieving the right balance - Mayo Clinic
Hypercalcemia is a condition that is defined by having too high of calcium levels in the blood. It is certainly possible to experience hypercalcemia by consuming too many calcium supplements, and certain diseases can also lead to high calcium levels in the blood, but the vast majority of the time, hypercalcemia is the result of thyroid dysfunction, specifically of hyperparathyroidism. The parathyroid gland produces the hormones that regulate calcium in the body.
Mild hypercalcemia may be asymptomatic or manifest as constipation, anorexia, nausea, and vomiting, with mental changes such as confusion, delirium, stupor, and coma becoming evident as the degree of hypercalcemia increases. Mild hypercalcemia usually is readily controlled by reducing calcium intake (e.g., decreasing the dose of or avoiding supplemental calcium); more severe hypercalcemia may require specific management (e.g., hemodialysis).
Medical tests can determine if a parathyroid disorder is the cause of high blood calcium.
In the presence of certain conditions, intravenous application of calcium-containing medication can lead to calcium overload. This abstract of the research paper listed below reminds us that calcium ion has long been known to play an important role in cell death regulation. Necrotic cell death was early associated with intracellular Ca2+ overload, leading to mitochondrial permeabilitytransition and functional collapse. Subsequent characterization of the signaling pathways in apoptosis revealed that Ca2+/calpain was critically involved in the processing of the mitochondrially localized, Apoptosis Inducing Factor. More recently, the calcium ion has been demonstrated to play important regulatory roles also in other cell death modalities, notably autophagic cell death and anoikis. In this review, we summarize current knowledge about the mechanisms involved in Ca2+ regulation of these various modes of cell death with a focus on the importance of the mitochondria.