Health

One thing is certain — the word is out about the importance of calcium. Thanks in part to the high-profile "Got Milk?" campaign, in which celebrities like Britney Spears and the cast of Everybody Loves Raymond model their milk mustaches and tout the bone-building power of dairy products, most Americans are aware of the value of calcium. Now, more foods than ever are fortified with calcium, including some cereals, orange juice, and certain kinds of margarine.

Still, most people aren't consuming enough of it. According to the National Osteoporosis Foundation, many women — young and old — get less than half the amount of calcium they need each day. (See "Getting the calcium you need" to find out how much calcium you should include in your diet.)

Most experts believe that it's best to get vitamins and minerals from food, rather than supplements, although scientists don't yet have a complete understanding of all the nutrients in food or how they work together. For example, the National Institutes of Health–sponsored Dietary Approaches to Stop Hypertension (DASH) study demonstrated that a high-calcium diet rich in fruits, vegetables, and low-fat dairy products can substantially lower blood pressure. But calcium supplements seem to have no effect on blood pressure, and they can increase the likelihood of developing kidney stones in people who are susceptible to them.

Dietary calcium

Luckily, if you want to increase your dietary calcium intake, you have plenty of calcium-rich foods from which to choose. Table 3 shows how much calcium is found in common foods. You may be surprised at how much you can accomplish by making a few substitutions, such as opting for firm versus regular tofu, or choosing ricotta instead of cottage cheese.

Calcium-rich dairy products Dairy products are rich in calcium.

As the table reveals, dairy products provide the most concentrated sources of calcium. Moreover, they're often fortified with vitamin D, supplying the daily requirement of that nutrient in one serving. For these reasons, many osteoporosis experts favor dairy products as a source of calcium. But dairy products have their detractors. Critics argue that many dairy products are high in unhealthy saturated fats and that they can cause gas, bloating, and diarrhea in people with lactose intolerance. They also cite research suggesting that people who consume a large amount of dairy products may be at greater risk for prostate or ovarian cancer.

In response, proponents of milk and other dairy products point out that an increasing array of reduced-fat milks, yogurts, and cheeses makes it possible to cut fat and calories without skimping on calcium. In fact, many of these products contain slightly more calcium than their high-fat counterparts do. It's also true that if you're lactose intolerant and have trouble digesting dairy products, lactase — either taken as a pill or in liquid form — can help you enjoy these foods without worrying about unpleasant side effects. You can even find some dairy products on your grocer's shelves that already have lactase added. And both sides of this debate acknowledge that more research is needed before it's clear whether dairy products affect the risk for prostate or ovarian cancer.

While milk and other dairy products are certainly a rich source of calcium, other foods can also help you meet your daily requirements. Just a cup of fortified orange juice supplies about 300 mg of calcium, and a cup of some fortified cereals, such as Whole Grain Total, offers 250 mg of calcium. The plant kingdom is also calcium-rich, with spinach, dried beans, and nuts among the best sources. However, the calcium content can't always be accepted at face value; some vegetables and grains contain substances that undermine calcium absorption. For example, the oxalic acid in spinach and rhubarb combines with the calcium in these plants so that it isn't readily absorbed. Insoluble fiber, such as that in wheat bran, also reduces calcium absorption, but soluble fiber, such as that in fruit pectins, does not affect calcium absorption. To further complicate matters, there is no easy equation for determining how much of the calcium content of a fruit or vegetable is actually absorbed.

Food labels, although helpful, often require translating. Packaged foods list calcium content not in grams per serving, but as a percentage of the FDA's Daily Value, which is 1,000 mg for all adults. (However, if you are trying to fill the daily calcium requirement recommended by the National Academy of Sciences, you may need 1,200–1,300 mg a day.) To determine how many milligrams of calcium per serving a product contains, multiply the percentage figure on the package by 10. So, for example, if a product's food label says that one serving provides 20% of your daily calcium requirement, that means it contains 200 mg of calcium.

Calcium supplements

While experts recommend getting your nutrients from foods instead of supplements, you may find that it just isn't practical or possible for you to get all the calcium you need from your diet. In that case, a supplement can shore up your calcium intake and your bones. In fact, a 2002 analysis of several studies of postmenopausal women found that the women who took calcium and vitamin D supplements for at least two years were 23% less likely to suffer a spinal fracture.

A dizzying array of calcium supplements is available — so many, in fact, that choosing one can be tricky. You can choose from flavored chews, pills, chewable tablets, and liquids. When making a decision, it's wise to consider cost, convenience, and how well your body tolerates the supplement (see Table 4).

The calcium in supplements is found in combination with another substance, typically carbonate or citrate. (Some products combine calcium with phosphate, lactate, and gluconate, but these are less common and tend to be more expensive.)

Calcium carbonate tends to be the best value, because it has the highest amount of elemental calcium. Elemental calcium is the actual amount of calcium in each supplement. The compound calcium carbonate contains 40% calcium by weight, while calcium citrate is 21% calcium. This means that you may need to take more tablets of a calcium citrate product in order to meet your daily needs.

Because calcium carbonate requires stomach acid for absorption, it's best to take this product with food. Most people tolerate calcium carbonate well. However, some people complain of mild constipation or feeling bloated. Some well-known calcium carbonate products include Caltrate, Viactiv Calcium Chews, Os-Cal, Tums, Rolaids Calcium Rich, and Liquid-Cal.

On the other hand, calcium citrate is absorbed more easily than calcium carbonate and can be taken on an empty stomach. But as mentioned above, you may need to take more tablets to get your daily requirement. Calcium citrate products include Citracal and GNC Calcimate Plus 800.

In weighing your options, check the labels of products to see what the serving size is and what the "% Daily Value" for calcium is. The "% Daily Value" reflects how much elemental calcium is in the product. The Daily Value is set by FDA regulations and is not the same as the Recommended Dietary Allowance (RDA). Currently, the Daily Value for calcium is 1,000 mg — the RDA for people ages 19–50, not the 1,200 mg RDA for older adults. Since the "% Daily Value" for all calcium supplements is 1,000 mg, simply multiply the percentage listed by 10 to find out how much elemental calcium the product contains. For example, if the label says the product contains 40% of the Daily Value, it has 400 mg of elemental calcium.

You'll find that the serving size and % Daily Value vary from product to product. For example, one Viactiv Soft Calcium Chew for Women contains 500 mg of calcium, while two Tums E-X antacids provide 600 mg. The same company may offer several different supplements, with varying amounts of calcium. For instance, with Citracal Calcium Citrate Tablets, you'll need to take two tablets to get 400 mg of calcium, while another Citracal formula, Citracal Calcium Citrate Plus Vitamin D, yields 630 mg of calcium in two caplets. In addition, some supplements may include vitamin D while others don't.

Reading the labels with an eye toward cost and convenience may help you sift through your options. Would you find it inconvenient to take several tablets at a time? How many tablets or chews does the package contain, how many must you take at a time, and what is your cost per serving? While products that yield a high amount of calcium may seem to be the best bet at first blush, they may not serve you best. Because your body has difficulty absorbing more than 500 mg of calcium at a time, more may go to waste. So while you may think that you've met your daily requirements by taking that 1,000-mg calcium pill, you may actually be only halfway to your target.

Your taste is another factor. You may find that you're more likely to remember to take your calcium if it comes in a soft caramel square, rather than a flavorless pill. Of course, preferences vary from person to person. Some people enjoy tropical fruit or berry-flavored antacids, while others find them chalky.

Here are a few other things to keep in mind when choosing and taking a calcium supplement:

• Generally, calcium pills are better choices than multivitamins, which tend to have small amounts of elemental calcium.
• The National Osteoporosis Foundation recommends avoiding calcium products from unrefined oyster shell, bone meal, or dolomite that don't have the United States Pharmacopeia (USP) symbol on them, since these products have tended to contain higher levels of lead, a toxic metal.
• Because calcium, iron, and zinc supplements interfere with each other, take them several hours apart.
• Delay consuming calcium (either from food or supplements) for two to four hours after taking tetracycline antibiotics, as calcium can decrease their effectiveness. Also, ask your doctor or pharmacist whether a supplement will interact with any prescription medications you're taking.

• Don't exceed the daily dose recommended by the manufacturer, since that increases the risk for side effects.
• Vitamin D helps your body absorb calcium, but it's not necessary to take vitamin D and calcium at the same time. However, if you aren't getting enough vitamin D from sunlight, your diet, or your multivitamin, you may want to choose a calcium supplement that contains this ingredient.
• To test how well the calcium in a supplement will be absorbed, put a tablet in 4 ounces of white vinegar and stir occasionally. If it doesn't dissolve in 30 minutes, it's not likely to dissolve in your stomach, which means it will simply pass through your body without being used.

Source: from Harvard Health Publications, Copyright © 2008 Harvard University. All rights reserved. Harvard Medical School does not endorse products.
Used with permission of StayWell.
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