Chalk, eggshells, milk, and bones have something in common. All get their dense white color from calcium—they’re loaded with it. Sharing this natural resource sometimes leads to some strange lend-lease arrangements. Bones and eggshells are often ground up for calcium supplements that go into livestock feed; then, from milk and other dairy products, we pick up some of the calcium that we need for better bones and other body-building biology projects. If we don’t get quite enough, we can turn to supplements that are often made from the basic geological substrata—the same mineral deposits that are sometimes used to make chalk.
We have more calcium than any other mineral in our bodies, and we’re right to associate it with bones because that’s where 99 percent of it is found. It’s vital throughout our lifetimes for building strong bones and teeth.
Calcium is used for much more, however. It’s also dissolved in the fluids in the body, those inside cells and those that bathe cells. There, it helps muscles spring into action and aids proper blood clotting. It assists nerves in transmitting impulses and helps launch hormones and enzymes on their journeys to inner organs.
Usually, the dissolved calcium in our bodies never gets so low that these important functions are impaired, but our bodies sometimes behave like poachers during lean times. Robbing Peter to pay Paul, they take calcium from bones as needed to make sure that the vital functions go on.
Like a Rock.......Not
Bones aren’t the inert, rocklike objects that we might imagine them to be. They are in a constant state of flux, dissolving and forming new bone all the time.
SUPPLEMENTSNAPSHOT
| Calcium Supplement forms: Calcium carbonate, citrate, citrate-malate, lactate, gluconate, and aspartate; dicalcium phosphate; bone meal; oyster shell; and dolomite. May help: Osteoporosis, high blood pressure, insomnia, menstrual cramps, muscle cramps, pregnancy-related high blood pressure, and restless legs syndrome. Daily Value: 1,000 milligrams. Special instructions: Divide your daily dose into two smaller doses, no more than 500 milligrams each. If you use calcium citrate, lactate, or gluconate, you can take it between meals without absorption problems, and it also won’t interfere with absorption of iron and other trace minerals. All other forms of supplemental calcium are best absorbed when taken with food. Avoid taking supplements at the same time as large amounts of wheat bran. To further aid absorption, get 400 international units of vita min D daily from sunlight, fortified foods, or supplements; it’s not necessary to take the supplements together. Who’s at risk for deficiency: People who don’t eat many dairy products, those who don’t get adequate vitamin D, and women who are pregnant or breastfeeding. Good food sources: Milk and milk products, sardines (with bones), kale, and calcium-fortified orange juice. Cautions and possible side effects: If you have had calcium oxalate kidney stones, check with your doctor before taking calcium. The supplements may slightly increase your risk of getting stones again. Supplements from natural sources—oyster shells, dolomite, or bone meal—may be contaminated with lead or other toxic metals; check labels for refined or purified sources. High doses may cause constipation. |
As bones begin to form, calcium salts form crystals on a gridwork of strands of a protein called collagen. These crystals invade the collagen and gradually lend more and more strength and rigidity to the developing bone. This happens with the speed of Federal Express deliveries when bones grow fastest, during childhood and adolescence; when a fractured bone is healing; and, indeed, throughout your lifetime. Bones reach their peak mass—when they’re strongest and most dense—in your late twenties. That’s why it’s so important to get enough calcium early on: The denser your bones are at their peak, the longer they’ll stay strong.
| What’s in the Bottles? Calcium comes in so many forms, even as a supplement, that choosing among the varieties may be confusing. Here’s a clue: When you’re reading labels, look for the “elemental calcium” listing to tell you how much you’re really getting, says Robert E. C. Wildman, Ph.D., professor of nutrition at the University of Delaware in Newark. Most labels include this listing, he adds. If the label does not indicate how much elemental calcium is in each tablet, you can use the table below. If you’re taking a 500-milligram tablet of calcium carbonate, for example, you can see that it contains 40 percent elemental calcium—which translates into 200 milligrams of calcium from each tablet. Here are the typical percentages of actual calcium in supplement products. Supplement Elemental Calcium (%) Calcium carbonate 40 Dicalcium phosphate 38 Bone meal 31 Oyster shell 28 Dolomite 22 Calcium citrate 21 Calcium lactate 13 Calcium gluconate 9 You don’t absorb all of the elemental calcium that’s in a tablet, Dr. Wildman points out—only about 30 to 40 percent (in fact, calcium citrate-malate, which is available mostly in fortified orange juice, is perhaps the best-absorbed form). If you take a supplement with food, a tablet of calcium carbonate is the most efficient way to get what you need. With supplements like calcium citrate, lactate, or gluconate, you’ll need to take more tablets to equal the amount of calcium in a single dose of calcium carbonate. |
The shipments of calcium need to continue well beyond that peak, however. "After that time, continuing to get enough calcium will help to reduce the rate of bone loss that occurs with aging," says Richard Wood, Ph.D., chief of the mineral bioavailability laboratory at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston.
For Muscles and Nerves
Calcium is also vitally important when it comes to properly functioning muscles, explains Lisa Ruml, M.D., a physician in Wharton, New Jersey. To contract and then relax, a muscle depends on the presence of calcium. "Calcium ions in the cell move from one spot to another very quickly, and that changes the electrical charge of certain proteins in the muscle cell so that the proteins change shape," she explains. These proteins tighten up and, in effect, pass along the tightening action to increase the tension.
As proteins shorten the muscle cells, the muscle contracts. When the calcium ions move back to their former positions, the proteins ratchet down from their state of peak tension, and the muscle relaxes. If you have too little calcium in your cells, however, the muscle cells tend to stay in the tightened position. You’ll become more prone to muscle cramps.
Along with other electrically aggressive minerals like potassium, calcium also allows our nerves to transmit messages. Because the electrically charged calcium ions in cells rapidly shift position, an electrical charge is handed along the chain of nerve cells. The result is that a small electrical current travels along the nerve. Once the current reaches the end of the nerve, it triggers the release of a neurotransmitter, a chemical that allows the message to be relayed to another cell.
In the heart, calcium’s role in both muscle contraction and nerve transmission comes into play. Calcium interacts with potassium and sodium over and over again in a carefully orchestrated sequence to produce a heartbeat. You would have to be seriously ill to be so low on calcium that it affects your heart, but it does happen. Doctors sometimes use drugs called calcium channel blockers to slow down and regulate heartbeat in people with high blood pressure, Dr. Ruml says. "These drugs temper the shift of calcium in and out of cells," she explains. Normally, however, getting more calcium isn’t going to help—or hurt—your heart.
Bowel Binder
In the intestines, calcium can combine with other nutrients and foods—such as saturated fat—to create compounds that cannot be absorbed into the body. In one study, a group of people getting 1,000 milligrams or so of calcium a day from fortified foods and 1,000 milligrams from supplements excreted twice as much saturated fat as people getting normal amounts of calcium. They also had an 11 percent drop in harmful LDL cholesterol.
| Calculate Your Calcium Needs Although calcium calculations may seem like higher math, there’s a simple way to figure out what you need. As a starting point, let’s say you get about 500 milligrams, which is the equivalent of about two cups of milk, and you’re aiming for the 1,200 milligrams that are recommended for many people. You’ll need to make up the shortfall with 700 milligrams of supplemental calcium each day, says Robert E. C. Wildman, Ph.D., professor of nutrition at the University of Delaware in Newark. If you know that your intake isn’t average—or you just like to play with figures—take the custom-tailored route. 1. Add up your daily servings of calcium champs—foods that you eat every day that supply substantial calcium. The champs most likely to be consumed daily (in single-serving amounts) are eight ounces (one cup) of 1 percent or fat-free milk, eight ounces of low-fat or nonfat yogurt, eight ounces of calcium-fortified orange juice, eight ounces of low-fat or nonfat calcium-fortified soy or rice milk, and two one-ounce slices of reduced-fat or fat-free cheese. After you’ve determined which of these you eat regularly, count 300 milligrams of calcium for each serving (or check labels, since calcium content can vary by brand). 2. To this number, add 200 milligrams for women and 300 milligrams for men, which is an estimated calcium total for all the other foods you eat throughout the day. 3. If you take a multivitamin/mineral supplement, add the amount of calcium that you get from that. (Don’t assume that a multi will cover your needs; most have too little calcium to make up average shortfalls.) 4. Subtract the total of steps 1, 2, and 3 from your daily requirement, 1,200 milligrams. Anything over zero is your daily shortfall and is the amount you should take in a supplement, says Dr. Wildman. |
Calcium may also play a role in preventing colon cancer by binding with cancer-promoting fats and bile acids, the digestive fluids secreted by the liver, says Dr. Wood. This neutralizes the toxic effects of the fats and acids, and if all goes well, they are excreted more rapidly, along with intestinal cells that might be cancer generators. But don’t count on miracles, he says. "The effects are fairly modest and occur only at amounts well above normal intake."
Calcium also helps to prevent the absorption of toxic minerals such as lead by interfering with cellular transport, says Dr. Wood. Unfortunately, it can interfere with minerals that we may need more of, such as iron, zinc, copper, and manganese. That’s why some doctors recommend that you not take calcium supplements with meals.
Coming Up Short
Women in the United States average between 700 and 800 milligrams a day of calcium. Men get nearly 1,000 milligrams, which is the DV. Some experts recommend higher amounts to protect against a deficiency, which results in more calcium being withdrawn from bones than is deposited.
Usually, you don’t know how frail your bones have become until you develop a condition called osteoporosis (the term means "porous bones"). At worst, your bones can become as riddled with holes as a termite-infested log and so fragile that simply bearing your own weight causes them to break.
Even if it’s not that bad, invisible damage can take its toll, eventually producing evidence that your bone skeleton has been starved of calcium. If you develop tiny fractures in your spine, you also end up with the bent-over stance called dowager’s hump, which many women accept as a sign of old age. Moreover, with osteoporosis, one fall can produce complicated and serious fractures. These are all good reasons to take calcium seriously and make sure that you’re getting enough.
