Calcium

6 October 2007

Calcium is vital for the development of healthy bones and teeth

The mineral calcium is vital for the development of healthy bones and teeth - 99 per cent of the calcium in our bodies is found in these places (a long-term shortage of calcium can lead to osteoporosis, when the bones become brittle and break easily).

It's also needed for muscle contraction, regulation of the heartbeat and is involved in the formation of blood clots.

Vitamin D is needed to help the body absorb calcium. It's made under the skin in response to sunlight and can also be found in foods such as cod liver oil, mackerel, canned salmon, eggs and milk.

The four pea-sized parathyroid glands are responsible for regulating the body's calcium levels. These small glands, which are embedded in the tissue of the thyroid gland, detect fluctuations in the level of calcium in the blood.

When the levels drop, they secrete parathyroid hormone (PTH). This causes calcium to be released from the bones, more to be reabsorbed through the kidneys and more to be absorbed from food in the intestines. If levels rise too much, PTH secretion is decreased and calcium levels return to normal again.

Too little calcium (hypocalcaemia) There are times when this delicate balance is upset and levels of calcium fall too low. This may be caused by chronic kidney failure, pancreatitis or problems with the parathyroid glands, which mean they don't produce enough PTH.

This last condition, called hypoparathyroidism, often occurs after damage to the parathyroid glands during surgery on the thyroid gland. Sometimes, however, it develops because of an autoimmune reaction where the body attacks itself.

When calcium levels are too low, calcium and vitamin D supplements are often required.

Occasionally, too much calcium enters the blood, most often as a result of cancer

Occasionally, too much calcium enters the blood, most often as a result of cancer that has spread to the bones. An overproduction of PTH may also responsible; this is often caused by a tumour in one or more of the parathyroid glands.

Excess production of PTH may occur to compensate for a malfunction in one of the body's other calcium-balancing mechanisms, for example, when the kidneys aren't working properly or when there's a deficiency of vitamin D.

Hypercalcaemia can also cause more serious problems such as depression, dehydration, bone fractures, kidney stones and sudden heart attacks.

Treatment depends on how high the levels of calcium are, symptoms and suspected underlying cause. Sometimes no treatment is necessary; at other times, intravenous drugs will be given to lower the calcium levels. Surgery may also be needed to remove the parathyroid glands if they're the source of the problem.