Calcium
Calcium (Ca) is essential to almost every function of the body. Most of these require only trace amounts.
| Link to a discussion of the many ways that tiny increases in the concentration of Ca2+ within cells alter their activity. |
Large amounts of calcium are needed to make bones (which are 18% calcium), so substantial amounts of calcium are needed in the diet during infancy and childhood.
The level of calcium (as its ion Ca2+) circulating in the blood is tightly controlled by:
Working together, they regulate how much is absorbed from food and how much spills over into the urine. Should the vertebrate body be faced with inadequate calcium in the blood, it can draw on the huge stores in the bones to make up the deficit.
Aging humans lose calcium from their bones so that in time they become fragile, a condition known as osteoporosis.
Osteoporosis is estimated to cause some 1.5 million fractures each year in the U.S. One in every three women who survive to age 81 will have suffered a hip fracture because of osteoporosis. (The rate for men of the same age is half that, presumably because men have sturdier bones to begin with.)
Avoiding Osteoporosis
- If you are older than 18 years (and younger than 71 years), get your recommended daily allowance (RDA) of 1000 mg of calcium, preferably in a soluble form (milk, milk products, or supplements containing calcium gluconate or calcium lactate).
- Be sure that your vitamin D intake meets the currently recommended daily allowance of 600 IU (international units).
- Exercise. It might help develop bone mass and even if it doesn't, it will be rewarding in other ways.
- For women after menopause, treatment with estrogen (or estrogen plus a progestin) seems to be an effective way to avoid osteoporosis. Many physicians feel that any risks of estrogen therapy (e.g., a possible increase in the risk of uterine cancer) are less than the clear hazards of osteoporosis. Time should tell.
- There are several non-hormonal drugs (e.g., alendronate) that slow bone loss by suppressing the activity of osteoclasts.
- Daily injections of a synthetic version of the parathyroid hormone, called teriparatide (Forteo®), build new bone by increasing the number and activity of bone-forming osteoblasts.
17 June 2011