Calcium is one of the most ubiquitous elements on the planet and one of the most important for the body. Type the keyword "calcium" into any Web browser and you are likely to find a host of products. Unlike drugs, there is no federal body that evaluates the safety and effectiveness of dietary supplements before they are put on the market, leaving that responsibility to the manufacturers. But the Federal Trade Commission and the Food and Drug Administration has issued warnings about the claims of a type of calcium supplement made from marine coral that its makers say is a cure-all for all sorts of conditions.

Still, experts say it's important to remember that calcium has a vital role to play in reducing risk of the bone condition osteoporosis, and in the function of the heart, nerves and muscle. Dr. Robert P. Heaney, a professor of medicine at the Creighton University in Omaha and the author of Calcium and Common Sense, has been studying calcium for more than 40 years. Below, Dr. Heaney discusses natural and supplemental sources of calcium, and explains how dietary calcium is unrelated to high blood calcium levels and calcium deposits in the body.

What is calcium, and what is its role in the body?
Calcium is one of the elements out of which the universe is made. It's very important for all of life. It's abundant in both fresh and marine waters. In humans, calcium is used by all cells for a variety of purposes, but perhaps most obviously calcium is the stuff that our bones are made of.

How much calcium do people need?
The Food and Nutrition Board publishes estimates of calcium requirements and the most recent ones were published in 1997. They recommend 800 mg per day up to age 8, and then 1300 mg per day through the growth years up to age 18, then 1000 mg per day out to age 50 and then 1200 mg per day thereafter.

That's the least you can get by on without some sort of a bone penalty. But the vast majority of Americans are not getting the recommended intake. Probably more than 80 percent of women, for example, are not getting the currently recommended intakes.

What are some of the primary foods sources for calcium?
The principal food sources in a modern diet, in the industrialized nations, would be dairy products, which are very calcium-rich. With dairy products, particularly milk and yogurt, the low-fat varieties provide all the nutrition of the full-fat varieties, but not the calories.

There are some other sources as well. Collard greens, which were popular in the Southern part of the United States, are a good source. Almonds, hazelnuts and Brazil nuts are pretty good sources of calcium. Certain kinds of shellfish can be good sources of calcium. Sardines and canned salmon, if eaten with the bones, are good sources of calcium. For vegetarians, tofu made with calcium can be a good source.

But as you can tell from the foods that I've cited, it's going to be hard to get enough of the calcium you'd like, because you're not going to eat all those things all the time every day.

We do have some calcium-fortified foods on the U.S. market. These include breads, breakfast cereals and fruit juices. They aren't as nutritious as dairy products but at least they can be high calcium sources.

What is the best way to obtain calcium?

It is preferable to obtain calcium from food. But the principle reason is that people who have a low calcium intake tend to have bad diets generally. In a study we published from our laboratory, a typical calcium-deficient person was also deficient in four out of eight other nutrients.

For example, in addition to providing calcium, the dairy products will give you a large fraction of your daily requirement for protein, phosphorus, vitamin D, magnesium, potassium, vitamin B6 and vitamin B12.

Supplements have an important role to play, but they should be what their name says they are. That is, they should supplement an otherwise good diet rather than try to substitute for a good diet.

When choosing supplements, is one better than another?

The one that's better is the one that you're going to stick with. Some supplements are based on different chemical forms of calcium. Some are based on calcium carbonate; some are based in calcium citrate. For all practical purposes, if made by a reputable manufacturer, they're all about the same.

Is there anything consumers should be wary of?

Consumers should stick to brand names. One of the most important things they should do is to avoid all of the hype and baseless claims. We've read in the news recently of the Federal Trade Commission and the Food and Drug Administration's clamping down on the outrageous and insupportable claims of certain coral calcium marketers. These marketers claimed that coral calcium cured cancer, heart disease, multiple sclerosis. And they claimed it cured both constipation and diarrhea, if you can believe that. They provided an endless list of things that were unsupportable and plainly false, and the quality of coral calcium is at best uncertain.

Calcium is important but it's too important to be given a black eye by unscrupulous promotion. So people should know that calcium is important. But they should also know that it's not a magic bullet and is not going to solve all the health problems of the human race.
What role does vitamin D play in absorption?

Vitamin D is essential for the absorption of calcium. The amount of vitamin D required is one of the most important, still open research questions in the field of nutrition today. It's now becoming clear from studies in a variety of laboratories that the body probably utilizes as much as 4000 International Units of vitamin D per day. Currently, the recommended daily intakes of vitamin D are only one-tenth of that, about 400 International Units per day. And that's what you're likely to get in a multivitamin tablet or capsule.

We probably need a lot more than we're getting by mouth, though most of our requirement is met when our skin is exposed to the sun when we go outdoors. That's because vitamin D precursors produced in the skin are acted on by the sun's ultraviolet rays to make vitamin D.

What can inhibit calcium supplement absorption?

If you take calcium supplements with food, not very much. Some foods such as spinach contain substances that block calcium absorption, but they block only the calcium that's in the spinach.

Caffeine interferes very slightly with calcium absorption. And that's more than offset with a little bit of milk. For example, if you have your coffee as a latté, you're actually coming out ahead of the game.

In general, most of the studies that have looked at alcohol consumption have found that people who have an average of maybe one to two servings of alcohol per day, may have better bones and seem to live longer than people who don't. So at least there isn't any evidence that that kind of mild drinking produces any harm.

Do calcium supplements interfere with absorption?

Calcium interferes with iron absorption. So, if you've had a major hemorrhage and you're trying to recover that blood loss by taking iron tablets, it would make good sense to separate your iron dose from your calcium supplements.

Calcium has a very slight interference with certain antibiotics such as tetracycline, which is used to treat acne. It's been shown that high doses of calcium can reduce the absorption of thyroid hormone. Again, it's a small effect, maybe 10 percent or 20 percent less absorption. I'm sure there are a few other drugs that would fall under the same category, but nobody has reported any major effects.

How does a low calcium intake result in lower bone mass?

Because calcium is so abundant in the environment, the human physiology evolved without having to learn how to conserve calcium because you always were going to get plenty with your next day's meal. And as a result, we don't hang onto calcium very well. We leak it out in the urine and in sweat. It comes out in sloughed, dried skin, hair, nails, etc.

Now all that calcium has to be replaced. Normally it would be replaced by the calcium in the food we eat. But when that's not true, then the body begins to tear down the bones in order to scavenge the calcium they contain. The body doesn't take the calcium out of the bones. It actually takes out units of bone itself, throws away the protein part and then uses the calcium.

Why do calcium deposits sometimes appear on X-rays?

Calcium gets deposited in essentially all dead or damaged tissue. For instance, if you've torn a shoulder ligament, you end with some scar tissue there. If you take X-rays, you may see some calcium deposits at the site of the tear.

The same is true of cancers. Now, of course, most of the cells in a cancer's growth are dying. They don't have the ability to continue to grow, and so you've got all this dead tissue and that's what gets calcified. That's what you're able to see on a mammogram. It really has nothing to do with the fact that it's cancerous. It's simply damaged or destroyed tissue.

What does it mean when someone has a high blood calcium level?

That means they have a disorder of the system that regulates blood calcium called hypercalcemia. It has nothing to do with their diet or the calcium intake.

We have a marvelous body regulatory system that controls that level of calcium very tightly. If we eat more calcium than we need, the body simply throws it away. It does not accumulate in the blood.

What is the role of calcium in people with kidney stones?

We now understand that kidney stones are actually better prevented with a high calcium intake than they are with a low calcium intake. And so, for somebody who has had kidney stones, cutting down on calcium intake is precisely the wrong thing to do. That will guarantee that they'll double their chances of having another kidney stone.

Does calcium reduce risk of any conditions other than osteoporosis?

Yes, though the effects are relatively small and it depends upon your sensitivity to those other conditions. Besides reducing risk of kidney stone formation, high calcium intake may reduce the risk of colon cancer.

A high calcium intake may also helps you lose weight if you're on a weight reduction regimen. Low calcium intakes force the body to secrete hormones that help conserve calcium. Some of the effects of these hormones cause the body's fat cells to go into storage mode. As a result, during dieting a low calcium intake tells the cells to hang onto the fat they have and try to get more. By contrast, a high calcium intake, by shutting down those adaptive hormones, switches the fat cells to a fat breakdown mode, and helps the body lose more weight. But calcium is not a magic bullet here. You still have to cut down on calories or you won't lose weight.

Other protective benefits probably include high blood pressure and the insulin resistance syndrome, and the so-called metabolic syndrome, which is associated with overweight.

What advice would you give to people about their calcium intake?
My recommendation is that the easiest thing to do is for everybody to get about 1200 to 1500 mg of calcium per day after childhood.

If you're not going to consume three to four servings of dairy products per day, then get it in some other form. But you need that much calcium to optimize your total body health, not just your bones.