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FAQ: Calcium Confusion

Posted by Dr. Suzanne Koven  March 13, 2013 07:18 AM

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calcium-rich-foods.jpg Certain questions come up frequently--daily!-- in my medical practice. Often these concern issues that have been reported heavily in the media and/or about which there is controversy. Here is the first in what will be an occasional series on this blog--"FAQ"--addressing some of the questions my patients ask me frequently. Please contact me at if there are medical topics which you think should be covered here in "FAQ."

One of the things about which I'm asked most commonly is calcium. Some of the confusion comes from the fact that our knowledge about calcium and health is evolving. A recent study showing that men who take calcium supplements have an increased risk of heart attacks is just the latest in an avalanche of sometimes conflicting information.

Here are a few of the questions I am most often asked about calcium, along with answers that reflect our knowledge--to date.

Why is calcium important?

Calcium, a mineral element, is a major component of bones and teeth. Smaller amounts are also necessary for normal function of the heart and other organs.

How much calcium do I need?

Here are the current recommendations for daily calcium intake from food and supplements combined. Most people, especially women and children, don't get enough calcium.

Life Stage Recommended Daily Intake

Birth to 6 months 200 mg
Infants 7–12 months 260 mg
Children 1–3 years 700 mg
Children 4–8 years 1,000 mg
Children 9–13 years 1,300 mg
Teens 14–18 years 1,300 mg
Adults 19–50 years 1,000 mg
Adult men 51–70 years 1,000 mg
Adult women 51–70 years 1,200 mg
Adults 71 years and older 1,200 mg
Pregnant and breastfeeding teens 1,300 mg
Pregnant and breastfeeding adults 1,000 mg

What's the best way to get enough calcium?

Various foods, including vegetables, fish, and dairy, are rich in calcium. Omnivores, vegetarians, and vegans can all get enough calcium in food--though it requires some effort and attention. Supplements are also available. Here's some good information on calcium-rich foods and supplements.

My blood calcium level is normal--doesn't that mean I get enough calcium?

No. The level of calcium in the blood is tightly regulated by various hormones (including parathyroid), the kidneys, and other organs. It does not reflect the store of calcium in the bones. In extreme cases, lack or excess of calcium intake can lower or raise blood calcium levels--both are dangerous.

Why are calcium supplements often combined with vitamin D?

Adequate vitamin D is required to absorb calcium in the intestines. Many people who live in northern climates or who don't get outdoors lack adequate vitamin D, since sunlight is necessary to metabolize it. Various foods such as fish, eggs, fortified milk and orange juice and others listed here provide vitamin D. It is a little challenging for vegans to get adequate vitamin D from food alone, but it can be done. Supplements may be necessary, especially for northerners, people who don't go out much, and people of color, who are more likely to be vitamin D deficient.

Does it matter when I take calcium supplements?

Yes, they should be taken with food (except calcium citrate, which is taken on an empty stomach), and not more than 500-600 mg at a time. You should also avoid taking calcium supplements with certain other medications including antibiotics and blood pressure medication (see below).

There are so many kinds of calcium supplements--does it matter which one I take?

Calcium supplements vary in dosage, chemical composition (calcium-carbonate, citrate, gluconate), form (powder, chewable or non-chewable pill, candy, liquid), and source (oyster shell, etc.)--not to mention cost. Here's a nice summary, including a "cheat sheet." If you find a certain product hard to swallow, constipating, too expensive, or unappealing for some other reason--switch.

If I have osteoporosis (bone thinning), will increasing my calcium intake help?

While inadequate calcium (and vitamin D) intake contribute to osteoporosis, supplementing these nutrients may not cure the problem. This landmark study showed that supplementation improved bone density, but didn't significantly lower the risk of fractures--the major complication of osteoporosis. For severe bone thinning, medication, in addition to calcium, vitamin D, and weight-bearing exercise, may be needed.

What's the down side to taking calcium supplements?

First, you can take too much. Excess calcium intake can lead to kidney stones, constipation, and other problems.

Second, calcium supplements can interfere with the metabolism of certain medications and should not be taken at the same time as these.

Third, some data suggests that calcium supplementation in men can cause heart disease (see above) and prostate cancer--though other studies have shown a decreased risk of cancer in those who take calcium.

So what's the bottom line?

Calcium is important for bone and general health--and most of us don't get enough of it. Ideally, we'd get what we need from food. If that's not possible, supplements are available--but we can't say confidently that these are 100% safe for everyone or that they are a fix for fragile bones.

This blog is not written or edited by or the Boston Globe.
The author is solely responsible for the content.

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About the author

Suzanne Koven, M.D. practices internal medicine at Massachusetts General Hospital in Boston. She writes a monthly column for the Globe's G Health section and her essays have appeared in the More »


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