calcium
Meaning of calcium: Bone acts as the bank: when blood levels dip, hormones withdraw calcium from the skeleton rather than let the level drift.
Definition of calcium
Calcium is a mineral the body needs both as a building material and as a signal. Almost all of it is locked into bone and teeth as a hard mineral salt that gives the skeleton its strength. The small fraction circulating in blood and inside cells triggers muscle contraction, carries nerve signals across junctions, and drives the cascade that clots blood.
How does the body hold the level steady?
| Signal | What it does |
|---|---|
| Parathyroid hormone | Released when blood calcium falls; frees calcium from bone, makes the kidney hold on to more, and switches on vitamin D |
| Active vitamin D | Increases how much calcium is absorbed from food in the intestine |
| Calcitonin | Released when calcium is high and lowers it modestly, with only a minor role in adults |
The tolerance is tight, because nerve and muscle cells misfire when the level strays far. Too little brings tingling around the mouth and fingers, cramps and, at the extreme, sustained muscle spasm. Too much brings thirst, constipation, confusion and kidney stones. The skeleton absorbs the shortfall when intake is low, which is why blood calcium can look perfectly normal while bone is quietly being spent to keep it that way.
Why can a blood calcium result mislead?
A large share of the calcium in blood is bound to proteins, mainly albumin, and only the free portion is biologically active. When albumin is low, as it often is in serious illness, the total measured calcium falls with it although the active fraction is unchanged. Laboratories either correct the total for the albumin level or measure the free portion directly. This is one of the standard traps in reading a report, and it explains results that appear alarming in someone with no symptoms at all.
What do calcium deposits outside bone mean?
Calcium salts can settle in tissue where they do not belong. Tiny deposits in the breast show up as bright specks on imaging; the great majority are harmless, but their shape and grouping occasionally suggest an underlying change worth sampling. Deposits build in the walls of arteries as atherosclerosis advances, in damaged heart valves, in tendons around the shoulder, and in the kidneys as stones. A deposit is a record of past injury or of a disturbance in mineral handling rather than a sign of eating too much calcium.
Also known as
Used in a sentence
A blood test was ordered to check the patient's calcium level as part of the metabolic panel.
Good to know
An abnormal blood calcium level more often reflects a problem with the parathyroid glands, vitamin D or the binding proteins in blood than with how much calcium is eaten.
Word origin
Where “calcium” comes from
From Latin calx, meaning lime, the material the element was first obtained from.