Keep Up Your Calcium
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
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
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
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
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
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
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.