Calcium, an Essential Element in the Diet
The Metal that Controls Many of the Processes that Keep Us Alive
Dec 9, 2008
As Blake observed, “Great things are done when men and mountains meet.” What the poet did not add, though he might just have been able to, as the metal was first isolated during his lifetime, was that without calcium, neither the men nor a significant number of the mountains would stand, let alone meet.
Calcium in the Body
The average human body contains about 1.2 kg of calcium. Approximately 1% of this is employed for tasks such as control of blood acidity, cell division, hormone release and in the electrical activity of nerves. The other 99% is present as calcium phosphate in the bones, teeth and finger nails. As well as providing the body’s support structure, bones act as a reservoir of calcium, from which the metal can be released into the blood to maintain the levels needed for these necessary functions to continue.
Despite their strength and durability, bones consist of living tissue in which, just like the rest of the body, material is being built up and broken down continually. Cells known as osteoblasts extract calcium from the blood and deposit it onto bone surfaces. At the same time, other cells, osteoclasts dissolve bone and return the calcium to the blood. This recycling is essential for preserving the balance of the metal throughout the body. The daily deposition of calcium onto new bone is about 400 mg, and an intake of 800 mg per day in the adult diet is recommended, with about 1200 mg for teenagers, in whom bone growth is more rapid. Milk, cheese and eggs are rich sources of calcium, as are broccoli and the bones present in canned fish.
Osteoporosis
From middle age onwards, calcium deposition slows down, leading to the bone weakening condition known as osteoporosis. Though this is more serious in women, it also affects men. Diet, exercise and in some cases drugs, can be used to slow down the process. In particular, hormone replacement therapy for women who have passed the menopause helps to minimise loss of calcium.
Osteoporosis is a progressive and serious problem faced by astronauts, the longer the time spent in space, the greater is the bone loss. If future astronauts are to spend long periods travelling, for example, to Mars or the outer planets, some way of solving this problem will need to be found. This makes research into the condition, by scientists working on the international space station, relevant not just to the tiny number of interplanetary travellers of the future, but to the vast majority of people who will forever remain earthbound.
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