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Calcium is a nutrient that is essential for strong bones and for supporting your body's critical functions such as controlling your blood pressure and maintaining your heart beat. Ninety-nine percent of your body's calcium is stored in your bones and teeth. This calcium makes up your bone bank. Throughout your lifetime, calcium is "deposited" in and "withdrawn" from your bone bank depending on your needs. When your dietary calcium intake is too low, your body will "withdraw" the calcium it needs from your bones. Over time, if more calcium is taken out of your bones than is put in, the result may be thin, weak bones that may break more easily.

Deficiency and Toxicity

Because bone stores of calcium can be used to maintain adequate blood calcium levels, short-term dietary deficiency of calcium generally does not result in significantly low blood calcium levels. But, over the long term, dietary deficiency eventually depletes bone stores, rendering the bones weak and prone to fracture. A low blood calcium level is more often the result of a disturbance in the body's calcium regulating mechanisms, such as insufficient PTH or vitamin D, rather than dietary deficiency. When calcium levels fall too low, nerve and muscle impairments can result. Skeletal muscles can spasm and the heart can beat abnormally—it can even cease functioning.

Toxicity from calcium is not common because the gastrointestinal tract normally limits the amount of calcium absorbed. Therefore, short-term intake of large amounts of calcium does not generally produce any ill effects aside from constipation and an increased risk of kidney stones. However, more severe toxicity can occur when excess calcium is ingested over long periods, or when calcium is combined with increased amounts of vitamin D, which increases calcium absorption. Calcium toxicity is also sometimes found after excessive intravenous administration of calcium. Toxicity is manifested by abnormal deposition of calcium in tissues and by elevated blood calcium levels (hypercalcemia). However, hypercalcemia is often due to other causes, such as abnormally high amounts of PTH. Usually, under these circumstances, bone density is lost and the resulting hypercalcemia can cause kidney stones and abdominal pain. Some cancers can also cause hypercalcemia, either by secreting abnormal proteins that act like PTH or by invading and killing bone cells causing them to release calcium. Very high levels of calcium can result in appetite loss, nausea, vomiting, abdominal pain, confusion, seizures, and even coma.

Dietary calcium supplements

Calcium supplements are used to prevent and to treat calcium deficiencies. There are conflicting recommendations about when to take calcium supplements. However, most experts agree that no more than 500 mg should be taken at a time because the percent of calcium absorbed decreases as the amount of calcium in the supplement increases. It is recommended to spread doses throughout the day, with the last dose near bedtime. Recommended calcium daily value intake varies from 1000 to 1500 mg, depending upon the stage of life.

Calcium supplements are widely used in the treatment and prevention of osteoporosis. Supplements are also recommended, or are being investigated, for a number of conditions, including hypertension, colon cancer, cardiovascular disease, premenstrual syndrome, obesity, stroke, and preeclampsia (a complication of pregnancy). There are several forms of calcium salts used as supplements. They vary in their content of elemental calcium, the amount effectively absorbed by the body, and cost. Whatever the specific form, the supplement should be taken with meals to maximize absorption.

Calcium carbonate is the most common and least expensive calcium supplement. It can be difficult to digest and causes gas in some people. Taking magnesium with it can help to prevent constipation. Calcium carbonate is 40% elemental calcium. 1000 mg will provide 400 mg of calcium. It is recommended to take this supplement with food to aid in absorption. In some calcium supplements based on calcium carbonate, vitamin D is added to aid in absorption. Vitamin D is needed for the absorption of calcium from the stomach and for the functioning of calcium in the body.

Coral Calcium is a salt of calcium derived from fossilized coral reefs. Coral calcium is comprised of calcium carbonate and trace minerals.

Calcium citrate is more easily absorbed (bioavailability is 2.5 times higher than calcium carbonate), easier to digest and less likely to cause constipation and gas than calcium carbonate. It also has a lower risk of contributing to the formation of kidney stones. Calcium citrate is about 21% elemental calcium. 1000 mg will provide 210 mg of calcium. It is more expensive than calcium carbonate and more of it must be taken to get the same amount of calcium.

Calcium phosphate costs more than calcium carbonate, but less than calcium citrate. It is easily absorbed and is less likely to cause constipation and gas than either.

Calcium lactate and calcium aspartate are both more difficult to digest and are more expensive than calcium carbonate

Calcium chelates have been chemically bonded with an agent that the body recognizes as food. This form is generally known to be better absorbed by the human body than all other forms of calcium due to the bond.

Buying Calcium supplements

The key factor to consider when buying calcium supplements is the amount of elemental calcium they contain. The term "elemental calcium" refers to the amount of calcium in a supplement that's available for your body to absorb. Most calcium supplements list the amount of elemental calcium on the label. But some brands list only the total weight — in milligrams (mg) — of each tablet. This is the weight of the calcium, plus whatever it's bound to — such as carbonate, citrate, lactate or gluconate.

The simplest way to determine how much elemental calcium is in a supplement is to look at the Nutrition Facts label. For calcium, the Percent Daily Value (% DV) is based on 1,000 mg of elemental calcium, so every 10 percent in the Daily Value column represents 100 mg of elemental calcium (0.10 x 1,000 mg = 100 mg). For example, if a calcium supplement has 60 percent of the Daily Value, it contains 600 mg of elemental calcium (0.60 x 1,000 mg = 600 mg).

When choosing a calcium supplement, you should also:

Note the serving size. This will tell you the number of tablets you must take to get the % DV listed on the label.

Check the label for the abbreviation "USP." The best supplements meet the voluntary standards of the U.S. Pharmacopeia (USP) for quality, purity and tablet disintegration or dissolution.

Be aware of generic brands. While generic calcium supplements are often cheaper than name brands, they may not meet voluntary standards for tablet disintegration. In other words, they may dissolve more slowly, which decreases their effectiveness.

Avoid calcium supplements that contain unrefined oyster shell, bone meal or dolomite. These products may also contain toxic substances, such as lead, mercury and arsenic.

Don't bother with chelated calcium tablets. They're more expensive and have no advantage over other types of calcium.

Recommended intake for calcium

The recommended intake for calcium is listed as an Adequate Intake (AI), which is a recommended average intake level based on observed or experimentally determined levels. Table 1 contains the current recommendations for calcium for infants, children and adults.

Know your daily recommended calcium intake

Age (years)	Calcium (mg*/day)
1-3	500
4-8	800
9-18	1300
19-50	1000
51 or older	1200
*mg=milligram Dietary Reference Intakes, National Academy of Sciences, 1997

Most individuals can easily get at least half of the calcium they need from food. If your typical calcium intake is too low, first try to increase the calcium in your diet. There are many calcium-rich foods to help you meet your calcium needs through diet alone.

If you are unable to modify your diet to get enough calcium on a daily basis, speak to your healthcare provider about taking a calcium supplement.

If you need a supplement, it is important to select one that contains the proper amount of calcium. Your daily recommended calcium intake minus the estimated daily calcium in your diet will determine how much calcium to take from a supplement.

Calcium Content of Selected Foods

Dairy	Calcium
Instant Breakfast	1 packet = 500mg
Milk, calcium fortifed	8 ounces = 400mg
Frozen yogurt, calcium fortifed	1/2 cup = 450mg
Yogurt	1 cup = 200-400mg
Ricotta cheese	1/4 cup = 250-300mg
Milk, cow's	8 ounces= 300mg
Buttermilk	8 ounces= 300mg
Mixed cheese dishes (1 serving = 1 slice pizza, 1 cup macaroni and cheese or 1 cup lasagna)	1 serving = 200mg
Cheese, sliced or shredded	1 ounce = 175-270mg
Creamed soup, made with milk	1 cup = 165-190mg
Cheese, string	1 ounce = 150-200mg
Cream cheese, fat free	2 Tablespoons= 150mg
Pudding	1/2 cup = 150mg
Cottage cheese, calcium added	1/2 cup = 120-200mg
Frozen yogurt	1/2 cup = 100-200mg
Ice cream, light	1/2 cup = 80-150mg
Ice pop (fudge, yogurt)	1 = 100mg
Cottage cheese	1/2 cup = 60-100mg
Parmesan cheese	1 Tablespoon = 40-60mg
Non-Dairy Alternatives (calcium fortified)	Calcium
Soy yogurt	6 ounces = 500mg
Soy or rice milk, calcium fortifed	8 ounces = 200-300mg
Soy cheese, calcium fortifed	1 slice = 200mg
Sour cream alternative	1 ounce = 100mg
Vegetable	Calcium
Vegetable juice, fortifed	8 ounces = 300mg
Amaranth, cooked	1 cup = 240mg
Turnip greens, cooked	1 cup = 200mg
Bok choy, cooked	1 cup = 160mg
Dandelion greens, cooked	1 cup = 140mg
Artichoke, boiled	1 medium = 135mg
Mustard greens, cooked	1 cup = 105mg
Kale, cooked	1 cup = 100mg
Broccoli, cooked	1 cup = 70mg
Broccoli, raw	1 cup = 40mg
Bread, Cereal, Rice and Pasta Group	Calcium
Ready-to-eat Cereal, calcium fort.	1 serving = 100-1000mg
Hot cereal, calcium fortifed (with water)	1 packet = 100-350mg
Waffes, calcium fortifed	2 = 300mg
Cheese crackers, calcium fortifed	1 serving = 100-250mg
Pancakes	1/3 cup batter = 100-200mg
Graham crackers, calcium fortifed	2 = 100mg
Bread, calcium fortifed	1 slice = 50mg
Tortilla, flour or corn	1-6 inch = 45mg
Fats, Oils and Sweets (use sparingly)	Calcium
Juice Drinks, calcium fortifed (10% juice)	8 ounces = 100-350mg
Cereal bars, highly sweetened, calcium fortifed	1 bar = 200-250mg
Cereal, highly sweetened, calcium fortifed	1 serving = 100-200mg
Milk chocolate granola bars, calcium fortifed	1 serving = 200mg
Molasses, blackstrap	1 Tablespoon = 170mg
Cookies, calcium fortifed	1 serving = 100mg
Meats, Poultry, Fish, Dry Beans, Eggs and Nuts Group	Calcium
Sardines, canned with bones	4 ounces = 350mg
Tofu, enriched with calcium	1/5 block = 300mg
Soy nuts, dry roasted	1/2 cup = 230mg
Salmon, canned with bones	3 ounces = 200mg
Cheeseburger	3 ounce = 100-150mg
Tahini	2 Tablespoons = 130mg
Egg substitute	1/2 cup = 130mg
Baked beans	1 cup = 130mg
Soybeans, green, boiled	1/2 cup = 130mg
Other beans, canned	1/2 cup = 40-60mg
Almonds	1 ounce = 80mg
Hummus	1/2 cup = 60mg
Fruit Group	Calcium
Juice, citrus varieties, calcium fortifed	8 ounces = 350mg
Figs, dried	5 = 135mg
Cherimoya	1 medium = 125mg
Juice, non-citrus varieties, calcium fortifed	8 ounces = 100-200mg
Juice box, calcium fortifed	8 ounces = 100-200mg
Papaya	1 raw = 75mg
Raisins, golden	2/3 cup = 50mg
Orange	1 medium = 50mg

See also: Iron in diet