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Eating Smart

Boning Up on Calcium-Supplement Facts

September 11, 2000|SHELDON MARGEN and DALE A. OGAR | Dr. Sheldon Margen is a professor of public health at UC Berkeley; Dale A. Ogar is managing editor of the UC Berkeley Wellness Letter. Send questions to Dale Ogar, School of Public Health, UC Berkeley, Berkeley, CA 94720-7360, or e-mail to

The list of foods naturally high in calcium is a familiar one by now: dairy products (especially nonfat), most dark green, leafy vegetables, and a few you might not think of such as figs, canned sardines and molasses.

But many people just do not get enough calcium from the food they eat. In fact, the average American consumes less than 800 milligrams of calcium per day. This is approximately the same as the recommended daily intake for a child age 4 to 8.

From about age 9 to young adulthood, a person's intake should be about 1,200 to 1,300 milligrams per day to account for growing bones. Adults need to be consuming at least 1,000 milligrams per day and older adults up to about 1,500 milligrams per day.

This calcium gap has left the door open to the manufacturers of calcium supplements, media hype and a lot of questions from consumers. There's not much we can do about the media hype, but maybe answering a few of the questions we have received about supplements will make it easier to ignore.

Question: How do I know which supplement is best?

Answer: Calcium supplements are available in a dizzying array of products. Every manufacturer tries to get your attention by making their product sound like the most complete and the best. Some of the claims made on the labels (like "all natural," "yeast free," "high potency") are just meaningless and tend to drive up the price. Remember the old adage--keep it simple.

Calcium as an element is not found uncombined, but as a compound. So the supplements always contain something else: carbonate, citrate, lactate, phosphate or gluconate. The dosage on the label is per pill, but the actual amount of calcium in each pill varies considerably, depending on the type of calcium in the product.

For example, calcium carbonate and calcium phosphate have the largest concentration of elemental calcium, about 40%. By contrast, calcium citrate has 21% calcium, calcium lactate has about 13% and calcium gluconate, only about 9%. This means that if you are taking a 500-milligram tablet of calcium carbonate you will be getting about 200 milligrams of actual calcium. In a 500-milligram calcium gluconate pill, you would only get 65 milligrams of calcium. To get the same 200 milligrams of calcium in the calcium carbonate pill, you'd have to take three tablets of the calcium gluconate. It's important to read the labels carefully.

There is very little evidence that any one form of calcium supplement is significantly more effective than another in preventing osteoporosis. Calcium carbonate is probably the cheapest, especially in the form of antacids, but oddly enough, at the doses needed to provide calcium supplementation, it may cause more gastrointestinal upset than the others. Calcium citrate, on the other hand, may be better absorbed.

Look for the "USP" marking on your calcium supplements. It means the product meets the U.S. Pharmacopeia's standard for dissolving and for dosage. The marking is most likely to be found on generic products that will cost significantly less than well-advertised brands.

Q: When is the best time to take calcium supplements?

A: In order to absorb calcium from supplements, it has to be dissolved into your bloodstream. Most of the time, only 20% to 30% of the calcium you consume is actually absorbed. Absorption rates differ depending on how much vitamin D is present and how old you are. After puberty, the rate goes down.

One way to increase the absorption of calcium is to take supplements with food and in doses of no more than 500 milligrams at each meal. If you are taking more than 500 milligrams of supplementation, spread it around with breakfast, lunch and/or dinner.

One of nature's dirty tricks is that many foods that are high in calcium also contain oxalic or phytic acid (spinach, rhubarb and wheat bran are examples) which inhibit calcium absorption.

Q: How much calcium is too much?

A: It appears that up to 2,500 milligrams a day is safe (at least from what we know so far). But the upper limit usually advised is 1,500. Whatever the body does not absorb is excreted. The most frequently reported side effects are constipation, intestinal bloating and excess gas. If you have any of these problems, you might want to switch the type of calcium you take or increase your fluid intake.

One cautionary note: People who are prone to forming calcium-containing stones in the urinary tract should probably not take supplements, but consuming too little calcium can also put some people at risk for stones. Calcium may also interfere with the absorption of other minerals and some drugs, so it's always a good idea to run the idea of supplementation past your health-care provider.

Q: What about calcium-fortified foods?

A: Be sure to read the labels of any foods fortified with calcium. The particular form of calcium (calcium malate) used to fortify some prepared foods may be slightly better absorbed, and it is important to add this source of calcium to the equation before you start supplementing with pills.


Eating Smart appears the second and fourth Mondays of the month.

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