Just the calcium facts.

How much? What kind? With meals? At bedtime? Here are the answers to some of the more common questions about calcium.

Q: Do I need a calcium supplement?

A: It depends on who you are (see "How Much is Enough?" p.6) and how much calcium you get from foods (see "The Calcium Counter,"p.9).

A rule of thumb: If you're a postmenopausal woman and don't eat at least four daily servings of high-calcium foods--like milk, yogurt, or calcium-fortified bread or juice--consider a supplement. For teens, make that at least three servings. For everyone else, two daily servings is enough.

Q: Which kind is best?

A: If you take it with meals, you're best off trying a factory-made calcium carbonate like Tums.

When calcium is paired with carbonate--rather than lactate, citrate, gluconate, or phosphate--you get the most calcium per tablet--as much as 500 or 600 mg. You usually also get the mostcalcium for your buck.

What's more, on average, calcium carbonate that's made in a factory-rather than natural carbonate from bone meal, oyster shell, or dolomite--has the least lead of any calcium supplement.(1) Bone meal has the most.

Q: What if I don't take it with meals?

A: On an empty stomach, calcium citrate is better absorbed than calcium carbonate. Older people especially may have trouble digesting calcium carbonate if they take it between meals. Apparently, their stomachs produce enough acid to break down the carbonate only during meals.

Calcium citrate may have another advantage: Some people say that calcium carbonate causes constipation or gas though neither problem is well-documented. And citrate is almost as low in lead as factory-made carbonate.

The downside is that calcium citrate contains only about 200 mg per tablet, so you'll have to take more tablets.

Q: Does it hurt my stomach to keep taking antacids?

A: Some, like Tums, have calcium carbonate as their only active ingredient, so they're no different than a calcium supplement. Others contain only magnesium hydroxide or aluminum hydroxide, so they're not good sources of calcium.

Some researchers used to worry that taking antacids all your life could cause "acid rebound"--that is, an increase in stomach acid between doses. In fact, there is little evidence that acid rebound is a problem in healthy people.(2)

Q: Do some supplements fail to dissolve?

A: That was true in the 1980s. But according to the researcher who discovered the problem, Ralph Shangraw, chair of the Department of Pharmacology at the University of Maryland, "the marketplace has changed in the last couple of years. We aren't finding bad tablets any more.

The only exceptions are calcium-magnesium combinations that occasionally don't break down, he adds.

Despite Shangraw's reassurance, there are things you can do to make sure your supplement breaks down:

* Look for a claim that mentions "USP" on the label. The U.S Pharmacopeia--which is charged with making sure that drugs are well-made--recently tightened its voluntary dissolution standards for calcium, and more companies are following them. The absence of a USP claim doesn't mean the supplement would fail the test, though. Many companies are simply waiting for new labeling regulations before changing their labels.

* Look for a supplement that mentions osteoporosis on the label. The FDA won't let supplements make claims about calcium and osteoporosis unless the tablets meet USP standards.

* If it's a chewable, make sure you chew it. "We've seen intestinal blockages in people who don't chew chewable antacids," says Shangraw.

Q: How often should I take a supplement?

A: While you absorb more if you take smaller amounts (like several 200-mg tablets throughout the day), it doesn't matter that much. So if you're the forgetful type, stick with one large dose. And whenever possible, take it with meals (or with a snack if you take it before bedtime).

Q: My Tums label says "1,250 mg calcium carbonate provides 500 mg elemental calcium." What does that mean?

A: The "elemental" tells you how much calcium--rather than carbonate, lactate, etc-- you're getting. It's the only number that means anything.

"I still get patients who come in taking 1,000 milligrams of calcium gluconate and think they're getting 1,000 milligrams of calcium," said John Eisman of the Garvan Institute of Medical Research in Sydney, Australia, at a recent conference on osteoporosis. "They're only getting 90 milligrams."

Q: Does the oxalic acid in chocolate or spinach keep me from absorbing calcium?

A: Only about five percent of the calcium in spinach is absorbed, compared to about 40 percent of the calcium in milk or in a vegetable like

But researchers think that something else in spinach compounds the problem, because pure oxalic acid doesn't impair absorption as much as spinach. The calcium in chocolate milk is well-absorbed, even though cocoa powder contains some oxalic acid.

Q: Does soda leach calcium from bones?

A: High levels of phosphorus in foods can keep the body from using calcium. That's why the FDA won't allow high-phosphorus foods to make claims about calcium reducing the risk of osteoporosis. That includes low-fat processed cheeses that are made with sodium phosphate.

A single soft drink isn't that high in phosphorus. But people who drink three to four 12-ounce cans a day do get enough to threaten their bones. Meat, fish, and poultry also add a lot of phosphorus.

Q: Are high-calcium supplements dangerous?

A: They appear to be quite safe. But if you or a member of your immediate family has had kidney stones, check with a doctor before taking any calcium supplement.

People who eat calcium-rich foods (not supplements) actually have a lower risk of kidney stones.(4) One explanation: Many stones are made of oxalate, and the calcium in foods may bind the oxalate before it can be deposited in the stone.

Despite calcium's apparent safety, there's no reason to consume more than 1,500 mg a day.

Q: Are vegans--vegetarians who eat no dairy products--at increased risk of osteoporosis?

A: Because most vegans eat less protein, they may lose less calcium in their urine. So it's possible that they need less calcium from their food. But so far, the evidence is shaky. In China, for example, bone density is higher in regions where milk products are consumed than in areas where people eat mostly rice and vegetables.(5)

Q: Do I need a vitamin D supplement to help me absorb calcium?

A: It depends on what you eat, your age, where you live, and how much you're outdoors.

The only foods with much vitamin D are fortified milk (but not yogurt, cheese, or other dairy foods) and fortified cereals. A glass of milk has 25 percent of the Daily Value, which is 400 IU. Most fortified breakfast cereals have ten percent. Fortunately, most of us get our vitamin D from the sun. The exceptions are:

* People who don't get out much. That's especially true for older folks, whose skin is less efficient at making vitamin D from the sun's rays.

* Northern residents in winter. Unless you live below 34 degrees north latitude--that is, in Southern California, Arizona, New Mexico, Oklahoma, Arkansas, Tennessee, North Carolina, or points south--the winter sun isn't strong enough to make sufficient vitamin D.

Q: Do magnesium or other nutrients reduce the risk of osteoporosis?

A: "No good evidence" is the refrain we heard from most researchers. That goes for boron, vitamin A, manganese, copper, iron--everything but vitamin D...and fluoride. Sodium fluoride taken with calcium does appear to prevent fractures, but fluoride is a drug that has to be carefully administered to avoid toxicity.(6)

(1)American Journal of Public Health 83: 1155, 1993.

(2)hepato-gastroenterology 29: 135, 1982.

(3)American Journal of Clinical Nutrition 51: 655, 1990.

(4)New England Journal of Medicine 328: 833, 1993.

(5)American Journal of clinical Nutrition 58: 219, 1993. (6) Annals of Internal Medicine 120: 625, 1994.

The Calcium Counter

Want a quick fix on your calcium intake? Start by giving yourself 300 mg for all the less-obvious sources combined, like bread, vegetables, and water. Then check the chart below for dairy, fortified foods, and other sources. It may be a crude estimate, but it's better than nothing.

Food                                                Calcium
                                                     (mg)
Wonder Calcium Enriched Bread (2 slices)              580
Lactaid Calcium Fortified Nonfat Milk (1 cup)         500
Yogurt, non-fat, plain (1 cup)                        452
Milk, skim, protein-fortified (1 cup)                 352
Tropicana Season's Best Orange
Juice Plus Calcium (1 cup)                            333
Milk, skim, regular (1 cup)                           302
Minute Maid Calcium Enriched Orange Juice (1 cup)     293
Swiss cheese (1 oz.)                                  272
Total cereal (3/4 cup)                                250
Cheddar cheese (1 oz.)                                204
Sardines, canned in water, drained (2 oz.)            185(1)
Collards, frozen (1/2 cup cooked)                     179
Ricotta cheese, part skim (1/4 cup)                   169
Ice cream or ice milk (1 cup)                         164
Tofu (3 oz.)                                          150(2)
Sherbet, orange (1 cup)                               103
Turnip greens (1/2 cup cooked, chopped)                99
Kale, frozen (1/2 cup cooked)                          90
Soybeans (1/2 cup cooked)                              88
Bok choy (1/2 cup cooked)                              79
Lowfat (2%) cottage cheese (1/2 cup)                   77
Parmesan cheese, grated (1 Tbs.)                       69
Orange (1 medium)                                      52
Swiss chard or kale (1/2 cup cooked, chopped)          49
Bread, white or whole wheat (2 slices)                 47
Pinto beans (1/2 cup cooked)                           41
Broccoli (1/2 cup cooked, chopped)                     36
Sweet potato, baked (1 medium)                         32

(1)Average of major brands.

(2)CSPI estimate of brands that use calcium sulfate or gypsum as a coagulant.

Sources: USDA handbook 8, Bowes and Church's Food Values of Portions Commonly Used, and manufactures.