Calcium

What it does

Calcium is the most abundant mineral in the body, and about 99% of it is locked into the skeleton and teeth, where it forms the hard mineral that gives them strength. Bone is not static, though — it is constantly being broken down and rebuilt, and a steady supply of calcium is needed throughout life to build a strong skeleton in youth and to slow its loss in later years, reducing the risk of osteoporosis and fractures.

The remaining 1% of the body's calcium, circulating in the blood and inside cells, is just as vital. It is essential for muscle contraction — including the steady beating of the heart — for the transmission of nerve signals, for the release of hormones, and for blood to clot. These functions are so important that the body keeps blood calcium within a very tight range, drawing it from the bones if the diet falls short. This is why a poor calcium intake harms the skeleton over time even when blood tests look normal.

Getting enough calcium depends partly on vitamin D, which is needed to absorb it efficiently from food. Dairy products are the richest common source, with useful amounts also in fortified plant drinks, tinned fish eaten with the bones, tofu set with calcium, and some green vegetables. Because calcium and its regulation are tightly controlled, both too little over the long term and very high supplement doses can cause problems.