Calcium

Calcium is the main structural mineral in the body. About ninety-nine percent of the body's three pounds of calcium is in the skeleton and teeth and is responsible for their hardness and strength. Calcium in the bones and teeth is not permanently stationed there, because the bones and teeth also serve as a reservoir for calcium. There is an almost constant exchange of calcium between the bones and the body fluids and soft tissues, where the rest of the calcium is located. Because the body's homeostatic mechanism maintains relatively constant blood levels of calcium, if dietary intake does not make up for what is lost through excretion, what is taken from the bones will not be replaced.

That one percent of the body's calcium outside the skeleton is also very important. It is essential for the strength of the intracellular membranes and for many important enzyme reactions involved in the clotting of blood and other processes; it regulates the excitability of peripheral nerves and muscles so that irritability is increased when calcium is low. Normal muscular contraction and relaxation, including the rhythm of the heart, depend on calcium.

Naturally, calcium is vitally important for growth and development. During the last trimester of pregnancy, between 200 and 300 mg. of calcium is deposited every day in the skeleton of the fetus. Breast milk contains from 250 to 500 mg. of calcium each day. If a pregnant or lactating mother isn't supplying this calcium in her diet, most of it is going to come out of her bones, and the bone health of both mother and child will suffer.

Since the body maintains fairly constant blood levels of calcium, low levels occur only in very severe deficiencies. When a deficiency is that bad, muscle spasms and convulsions usually occur. Researchers use what is called calcium "balance" to measure a person's calcium status. The total intake of calcium is measured and compared to the total amount excreted through the urine, feces, and sweat. When the amount excreted is about the same as that ingested, calcium balance is zero, or even. When more calcium is excreted than ingested, calcium balance is negative. And when more calcium is ingested than is excreted, balance is positive.

The balance method is far from perfect, especially since many factors can affect calcium retention and excretion. But when researchers are careful to eliminate or account for as many of these factors as possible, and when the tests are done over a fairly long period, calcium balance can be a good indicator of whether a person is getting enough calcium in the diet.

Another method is to actually measure and compare the density of the bones over various lengths of time. This method, of course, is the best way to find out if enough calcium is being supplied in the diet, because if the diet is deficient, the bones lose calcium and become less dense.

Insufficient dietary calcium can be a factor in rickets, osteomalacia, and osteoporosis.

Besides its effects on bone mineralization and nerve and muscle irritability, calcium deficiency can also affect blood and tissue levels of two poisonous metals, lead and cadmium. When dietary calcium is low, the body retains more lead. This has been demonstrated in several experiments with both humans and animals: low dietary calcium causes high blood and tissue levels of lead.

Low dietary calcium actually causes animals to eat more lead. Calcium deficient rats and monkeys voluntarily consume up to forty-four times the amount of lead via lead-containing water than they will under normal circumstances, even when pure water is available. Injecting the animals with toxic levels of lead still does not erase or diminish their preference for lead. Since human studies have demonstrated that children deficient in calcium also have higher blood levels of lead, there appears to be a connection between lead poisoning and calcium deficiency. The real villain in lead poisoning may not be lead in paint, but inadequate diet.

Cadmium, another toxic pollutant, is also retained by the body in higher concentrations when calcium is low.

The RDA for calcium ranges from a low of 360 mg. for infants to a high of 1200 mg. for pregnant and lactating women. The RDA for adults, both men and women, is 800 mg.

For a newborn baby, the best source of calcium is mother's milk, which has a calcium-phosphorus ratio of 2.4:1. Cow's milk, with a ratio of 1.2:1, is a good source for everyone else, but is not the only good natural source of calcium. Egg yolk, fish (eaten with the bones), soybeans, green leafy vegetables such as turnip greens, mustard greens, broccoli, and kale; roots, tubers, and seeds; and stews and soups made with bones can provide considerable calcium. Lactose (the sugar found in milk and milk products) has a positive effect on calcium absorption.

Supplements of calcium are available in many forms (calcium carbonate, calcium gluconate, calcium lactate, etc.). There is no general agreement over which form is the best. It is probably wise to use more than one form in a supplement program. (Don't forget that vitamin D also is necessary for calcium absorption and utilization.) Calcium supplements are available in a wide range of dose levels, from less than 100 mg. to several hundred milligrams.

Where is it found ?

Most dietary calcium comes from dairy products. The myth that calcium from dairy products "doesn't absorb" is not supported by scientific research. Other good sources include sardines, canned salmon, green leafy vegetables, and tofu.

Choosing a form of calcium supplement can be confusing. While fewer pills of the calcium carbonate form are needed, this form doesn't absorb as well as some other forms of calcium. Most, but not aII, studies suggest that calcium citrate is better absorbed than calcium carbonate. Virtually all comparative studies find that calcium citrate/malate (CCM) absorbs somewhat better than calcium carbonate. CCM is increasingly the form of calcium recommended by nutritionally oriented doctors. The microcrystalline hydroxyapatite (MCHC), a variation on the bonemeal form of calcium, has been shown to improve bone mass,  but the absorption of MCHC appears to be poor. Only preliminary research exists regarding the amino acid chelates of calcium, and conclusions, cannot be drawn at this time.

Who is likely to be deficient ?

Severe deficiency of both calcium and vitamin D is called rickets in children and osteomalacia in adults. Vegans (pure vegetarians), people with dark skin, those who live in northern climates, and people who stay indoors almost all the time are more likely to be vitamin D deficient than are other people. Vegans often eat less calcium and vitamin D than do other people. Most people eat well below the recommended amount of calcium. This lack of dietary calcium is thought to contribute to the risk of osteoporosis, particularly in white and Asian women.

How much to take

The National Academy of Sciences has established guidelines for calcium that are 25-50% higher than previous recommendations. For ages 19 to 51, calcium intake is recommended to be 1,000 mg daily; for adults over age 51, the recommendation is 1,200 mg daily. The most common supplemental amount for adults is 800-1,000 mg per day. General recommendations for higher intakes (1,200-1,500 mg) usually include the several hundred milligrams of calcium most people consume from their diets.

Side effects

Constipation, bloating, and gas are sometimes reported with the use of calcium supplements. A very high intake of calcium from dairy taken with calcium carbonate used to cause a condition called "milk alkali syndrome." This toxicity is rarely reported today because most medical doctors no longer tell people with ulcers to take this combination.

People with hyperparathyroidism, or chronic kidney disease should not supplement with calcium without consulting a nutritionally oriented physician. People who have had kidney stones should consult the doctor before considering supplementation. For other adults, the highest amount typically suggested by nutritionally oriented doctors (1,200 mg per day) is considered quite safe.

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