Of all the essential minerals, calcium's role in our diet-to build strong bones and teeth-may be most well known. Less well known is that it's also critical for the functioning of our heart, nerves, muscles and other bodily systems. According to the experts, insufficient calcium not only contributes to osteoporosis but has also been associated with obesity, precancerous colon polyps and cognitive decline in people 65 and over. Despite playing such vital roles, only one American in five consumes an adequate amount. Knowing how much we need and why, along with where to get it from are the first steps in closing this gap.

According to the daily Dietary Reference Intakes (DRIs) for calcium, children one to three years old need 500 milligrams (mg); children four to eight years old need 800 mg; preteens and teenagers need a significant amount of 1,300 mg per day; those 19 to 50 need 1,000 mg; after age 50, the recommendation rises to 1,200 mg. The National Institutes of Health recommend an even higher amount, 1,500 mg, for people over 65. As an upper limit, experts advise taking no more than 2,500 mg, as calcium toxicity, although extremely rare, can occur with excessive long-term consumption (over 3,000 mg/day).

While it’s true that you store calcium and build bone most efficiently into your early 30s, it’s never too late to increase your calcium intake to improve bone health and meet your other critical needs. Because bone is living tissue that becomes stronger with exercise, increasing your physical activity while consuming adequate amounts of calcium can help you to build stronger bones at any age. The best bone-building exercises are those that are weight-bearing such as walking, dancing, jogging, stair-climbing, racquet sports and hiking.

While bone loss accelerates with age in both men and women, bone loss is particularly common in post-menopausal women, when the ovaries stop producing estrogen, the hormone that protects against bone loss. If too much calcium is lost, osteoporosis, or porous bone, may develop. Characterized by low bone mass and structural deterioration of bone tissue, osteoporosis can lead to bone fragility and an increased susceptibility to fractures, especially of the hip, spine and wrist. According to the National Osteoporosis Foundation, women are four times as likely to have the disease as men and can lose up to 20 percent of their bone mass in the five to seven years following menopause. A bone mineral density (BMD) test is the only way to diagnose osteoporosis and determine your risk for future fracture. Since osteoporosis can develop undetected for decades until a fracture occurs, early diagnosis is important.

The Coop is a great place to find many different sources of calcium. While dairy products may be the best known sources of calcium, many vegetables contain calcium too. However, the calcium in vegetables is not absorbed equally. The best vegetable sources of calcium include broccoli, bok choy, Chinese/Napa cabbage, okra and leafy greens like kale, collards, and turnip greens. Less well absorbed is the calcium in spinach, chard and beet greens. For those who choose not to consume dairy products and eat few of the vegetable sources, there is a plethora of calcium-fortified soy products, juices, cereal and bread products. Lactose-intolerant individuals who wish to include dairy products in their diets can find lactose-reduced dairy products and lactase enzyme capsules.

Calcium supplements are available in a wide range of preparations and strengths, and can easily be found in the Coop’s well-stocked supplement section. The two main types of calcium supplements are calcium carbonate and calcium citrate, depending on the compound that is combined with the calcium. Since the actual amount of calcium is referred to as "elemental calcium," it is important to read the label carefully to determine how many doses or pills to take. While calcium carbonate is relatively inexpensive, widely available, and contains twice as much calcium as a comparable amount of calcium citrate, it can be difficult to digest and should be taken with food. Calcium citrate, on the other hand, can be taken anytime and may be more easily digested. Other supplements include calcium lactate, calcium gluconate and calcium phosphate.

Calcium is also commonly combined with other vitamins and minerals such as vitamin D, which is necessary for calcium absorption, and magnesium, which is also important for bone health. Protein also plays a role in calcium absorption. Recent studies have shown that with adequate calcium and vitamin D intake, protein consumption can enhance absorption; but without them, protein may actually reduce absorption. However, the exact amount of protein consumed to cause these effects is not well understood yet.

When choosing a brand, experts advise choosing supplements with labels that state "purified" or have the USP (United States Pharmacopoeia) symbol. These products have met national voluntary quality standards of purity and dissolution, so are less likely to contain harmful contaminants and are more likely to dissolve in your stomach. Experts particularly warn against choosing brands without the USP symbol when the calcium is from unrefined oyster shell, bone meal or dolomite, as these historically have contained higher lead levels or other toxic metals.

In terms of absorption, chewable, liquid and powder calcium supplements dissolve best, because they are broken down before they enter the stomach. Although most people don't experience side effects, calcium supplements may cause gas or constipation, which can be resolved with increased fluids and fiber intake. Finally, whether from the diet or supplements, calcium is best absorbed by the body when it is taken several times a day in amounts of 500 mg or less; but consuming it all at once is better than not taking it at all.

In the end, the "best" supplement is the one that meets an individual's needs. It is also important to talk with a physician or pharmacist about possible interactions between prescription or over-the-counter medications and calcium supplements.

References

American Dietetic Association. 1997. "Nation's Nutritionists Help Americans Understand New Intake Recommendations." Online at www.eatright.org/Public/SearchResults.cfm .

Barbara Eisenhaure. 2003. "Calcium Debate: How much is enough?" Online at www.nutrition.tufts.edu/magazine/2003spring/calcium.html .

National Osteoporosis Foundation. Online at www.nof.org .

Sara Ivry. 2003. "When it comes to calcium, the advice is to keep eating." New York Times (June 22).

Calcium Content of Selected Vegan Foods

 Food Amount Calcium (mg) 

* Read the label on your tofu container to see if it is processed with calcium sulfate or nigari.

Note: Oxalic acid, which is found in spinach, rhubarb, chard, and beet greens is often said to bind with calcium and reduce absorption. These foods should not be considered good sources of calcium. Calcium in other green vegetables, like kale, collard greens, Chinese mustard greens, and Chinese cabbage flower leaves is well absorbed. Fiber appears to have little effect on calcium absorption, except for the fiber in wheat bran, which does have a small effect.