Calcium is the most abundant mineral in the body. It is essential for the development and maintenance of strong bones and teeth; roughly 99% of calcium in the body is deposited in these two places. Calcium also helps the heart, nerves, muscles, and other body systems work properly. To function correctly, calcium must be accompanied by several other nutrients including magnesium, phosphorous, and vitamins A, C, D, and K.

The best sources of calcium are foods (see Dietary Sources), but supplements may be necessary for those who cannot meet their calcium needs through diet alone. In fact, according to the National Institutes of Health, many Americans consume less than half the amount of calcium recommended to build and maintain healthy bones. Heavy use of caffeine can diminish calcium levels; therefore, higher amounts of calcium may be needed if you drink a lot of coffee. Also, a diet high in protein can increase loss of calcium through the urine. Excessive intake of sodium, phosphates (from carbonated beverages) and alcohol, as well as the use of aluminum-containing antacids also contribute to increased excretion of calcium.

Calcium deficiency can be found in people with malabsorption problems, such as Crohn's disease, celiac disease, and surgical intestinal resection. Prolonged bed rest causes loss of calcium from the bones and the elderly are less able to absorb calcium.

Symptoms of calcium deficiency include muscle spasm or cramping, typically in hands or feet; hair loss (alopecia); dry skin and nails which may also become misshapen; numbness, tingling, or burning sensation around the mouth and fingers; nausea and vomiting; headaches; yeast infections (candidiasis); anxiety; convulsions/seizures; and poor tooth and bone development.

Obtaining adequate calcium can help prevent and/or treat the following conditions:

Osteoporosis

An inadequate supply of calcium over the lifetime is thought to play a significant role in contributing to the development of osteoporosis. Calcium is necessary to help build and maintain healthy bones and strong teeth. Studies have shown that calcium, particularly in combination with vitamin D, can help prevent bone loss associated with menopause, as well as the bone loss experienced by elderly men. If adequate amounts of calcium are not being obtained through the diet, calcium supplements are necessary.

Hypoparathyroidism

This condition, which represents under active parathyroid glands, requires lifelong treatment with calcium along with vitamin D. The parathyroids are four small glands that sit on the four corners of the thyroid in the neck and produce a hormone that regulates calcium, phosphorous, and vitamin D levels in the body. People with this condition should follow a high calcium, low phosphorous diet. Therefore, milk and cheese should not be the sources of calcium used since dairy foods contain phosphorous as well. Most often, supplementation is needed in addition to dietary sources of calcium for this condition.

Premenstrual Syndrome (PMS)

Calcium levels often measure lower the week prior to one's menstrual period compared to the week after. Studies suggest that calcium supplementation helps relieve mood swings, food cravings, pain or tenderness, and bloating associated with premenstrual syndrome.

High Blood Pressure

Studies of people with hypertension have found that the addition of low-fat dairy products to a diet rich in fruits and vegetables may lead to a greater improvement in reducing blood pressure than the typical American diet or a diet rich in fruits and vegetables alone. Some experts believe that the calcium in these low-fat dairy products is responsible for the improvement; however, given that dairy products also contain other nutrients (such as magnesium and potassium), that conclusion is not entirely clear. In addition, studies that have investigated calcium as a supplemental treatment for high blood pressure have not been conclusive; in other words, it remains to be seen whether taking supplements of calcium will have the same effect on blood pressure as low-fat dairy products in the diet.

Given the safety and possible benefits of calcium supplementation in the treatment of high blood pressure, however, many integrative medicine practitioners feel that it is worth a try. At least 6 to 8 weeks of calcium supplementation may be needed before noting an improvement in blood pressure. Do not stop blood pressure medication when taking calcium; work with your physician who will guide the adjustment of medications if necessary.

Some studies suggest that calcium supplementation may play a role in the prevention of pregnancy-induced high blood pressure and preeclampsia. (Preeclampsia is a worrisome combination of high blood pressure, fluid retention, and high levels of protein in the urine that some women develop in the last trimester of pregnancy.) A prenatal vitamin, which provides magnesium, folic acid, and many other nutrients, together with adequate calcium intake may significantly lower the risk of developing high blood pressure during pregnancy.

High Cholesterol

Preliminary studies in animals and people suggest that calcium supplements, in the range of 1,500 to 2,000 mg per day, may help to lower cholesterol. The information available thus far suggests that keeping cholesterol levels normal or even low by using calcium supplements (along with many other measures such as changing your diet and exercising) is likely to be more beneficial than trying to treat it by adding calcium once you already have elevated cholesterol. More research in this area is needed.

Stroke

In a population based study (one in which large groups of people are followed over time), women who take in more calcium, both through the diet and with added supplements, were less likely to have a stroke over a 14 year time course. More research is needed to fully assess the strength of the connection between calcium and risk of stroke.

Colon Cancer

Although some studies are conflicting, mounting evidence suggests that people who consume high amounts of calcium, vitamin D, and milk in their diets are significantly less likely to develop colorectal cancer than those who consume low amounts of the same substances. Although it is best to obtain calcium from the diet, the suggested amounts for the prevention and treatment of colorectal cancer (namely, 800 IU/day of vitamin D and 1,800 mg/day of calcium) will most likely require supplementation.

Obesity

Both animal and human studies have found that dietary calcium intake (from low-fat dairy products) may be associated with a decrease in body weight. These effects cannot necessarily be attributed to calcium alone since dairy sources of calcium contain other nutrients (including magnesium and potassium) that may be involved in the weight loss. A review of all studies up to the year 2000 did conclude, however, that supplementation of 1,000 mg of calcium can facilitate as much as 8 kilograms (17.6 pounds) of weight loss and 5 kilogram (11 pound) loss of fat.

Tooth and Gum Disease

Calcium and vitamin D supplementation may slow the rate of tooth loss in the elderly. Studies have also suggested that adolescent girls who consume more calcium in their diets are less likely to develop gingivitis (gum disease) than those who do not consume as much calcium.

Rickets
This condition, which leads to softening and weakening of the bone in children, is due to vitamin D deficiency. Although virtually eliminated in North America and Western Europe because milk is fortified with vitamin D, it still occurs in many parts of the world. The mainstay of treatment has been supplementation with vitamin D. A recent study, however, suggests that the addition of calcium may be at least as important as vitamin D for treating rickets, if not more so.

Insomnia

Although not studied scientifically, some people report that calcium helps them sleep better.

The richest dietary sources of calcium include cheeses (such as parmesan, romano, gruyere, cheddar, American, mozzarella, and feta), wheat-soy flour, and blackstrap molasses. Some other good sources of calcium include almonds, brewer's yeast, bok choy, Brazil nuts, broccoli, cabbage, dried figs, kelp, dark leafy greens (dandelion, turnip, collard, mustard, kale, Swiss chard), hazelnuts, ice cream, milk, oysters, sardines, canned salmon soybean flour, tahini, and yogurt.

Foods that are fortified with calcium, such as juices, soy milk, rice milk, tofu and cereals, are also good sources of this mineral.

Calcium may also be obtained from a variety of herbs, spices, and seaweeds. Examples include basil, chervil, cinnamon, dill weed, fennel, fenugreek, ginseng, kelp, marjoram, oregano, parsley, poppy seed, sage, and savory.

There are a number of forms of calcium available as dietary supplements. They differ in the amount of calcium they contain, how well they are absorbed by the body, and cost. Following is a list of commonly used calcium supplements.

• Calcium citrate: Many have found that this supplement is absorbed and digested by the body more effectively than calcium carbonate, particularly in the elderly, and appears to be more effective than calcium carbonate in preventing osteoporosis in postmenopausal women. It is more costly than calcium carbonate, however. Also, calcium citrate should not be used with aluminum-containing antacids (see Possible Interactions).
• Calcium carbonate: This supplement may not be as effective as calcium citrate, but is less expensive. Sufficient stomach acid is required to absorb calcium carbonate, but many older people (particularly postmenopausal women) have low stomach acidity. For such individuals, calcium citrate is more appropriate. Many antacids contain calcium carbonate.
• Calcium gluconate
• Calcium lactate
• Calcium chloride: This form is not recommended as it has been shown to irritate the gastrointestinal tract.

Calcium supplements that are derived from oyster shells, dolomite, and bone meal are best avoided as they may contain lead. Rarely, traces of lead are found in other types of calcium supplements as well. Lead is a toxic metal (particularly worrisome in children and those with kidney disease) that can harm the brain and kidneys, cause anemia, and raise blood pressure. On a positive note, however, calcium seems to block the absorption of lead. Nonetheless, it makes sense to look for labels on all types of calcium supplements that indicate they have been tested for lead content.

Calcium supplements should be taken in small doses (no more than 500 mg at a time) throughout the day with 6 to 8 cups of water to avoid constipation.

The following are daily dietary recommendations for general health and prevention of disease.

Pediatric

• Infants birth to 6 months: 210 mg
• Infants 7 months to 1 year: 270 mg
• Children 1 to 3 years: 500 mg
• Children 4 to 8 years: 800 mg
• Adolescents 9 to 18 years: 1,300 mg

Adult

• 19 to 50 years: 1,000 mg
• 51 years and older: 1,200 mg
• Pregnant and breastfeeding females under 19 years: 1,300 mg
• Pregnant and breastfeeding females 19 years and older: 1,000 mg

For prevention of colon cancer, 1,800 mg per day may be required.

Because of the potential for side effects and interactions with medications, dietary supplements should be taken only under the supervision of a knowledgeable healthcare provider. Total calcium intake, from combined dietary and supplemental sources, should not exceed 2,500 mg per day.

Common complaints when taking calcium supplements include constipation and stomach upset. Symptoms that may occur from excessive amounts of calcium in the blood include nausea, vomiting, loss of appetite, increased urination, kidney toxicity, confusion, and irregular heart rhythm. These symptoms resolve when elevated calcium levels are treated and brought back to normal.

Such high levels of calcium in the body may develop from either ingesting very large amounts (5,000 mg per day, or more than 2,000 mg per day over a long period) or, more likely, from the body producing too much calcium. The latter may occur with certain types of cancer or from hyperparathyroidism (an over active parathyroid gland which produces a hormone to regulate levels of calcium, phosphorous, and vitamin D). Kidney failure, breakdown of bone, and excessive levels of vitamin D may all lead to elevated calcium as well. Calcium supplements must not be taken in any of these situations.

Interestingly, people with a history of kidney stones (which contain calcium) had often been advised to consume a diet low in calcium in order to avoid recurrent stones. However, a new study indicates that a diet containing normal amounts of calcium and reduced amounts of animal protein and salt may provide an even greater protective effect against recurrent kidney stones. In other words, it is quite likely that calcium intake does not need to be restricted in those with a history of kidney stones, especially if animal protein and salt intake are restricted. Additional research will be helpful in better understanding the relationship between kidney stones and calcium.

High calcium intake from dairy products may actually increase a man's risk of prostate cancer. In one important population based study, following a large group of men over an 11 year time course, men who consumed more than 600 mg/day of calcium from dairy products had an increased risk of prostate cancer compared to men who ate less than 150 mg/day from dairy. (The reason that calcium is suspected is because it prevents the conversion from one form of vitamin D to another, more protective form known as 1,25-dihydroxyvitamin D3. The latter form of vitamin D inhibits prostate cancer cells in test tubes.) However, more research is need in this area since it may be some other component in dairy products that is responsible for the increased risk of prostate cancer. In the meantime, men should try to obtain their calcium from non-dairy sources.

If you are currently being treated with any of the following medications, you should not use calcium supplements without first talking to your healthcare provider

Alendronate
Calcium may interfere with the absorption of alendronate, a medication used to treat osteoporosis. Calcium containing products, therefore, should be taken at least two hours before or after alendronate.

Antacids, Aluminum-containing
When calcium citrate is taken with aluminum containing antacids, the amount of aluminum absorbed into the blood stream may be increased significantly. This is a particular problem for people with kidney disease in whom the aluminum levels may become toxic. In addition, aluminum-containing antacids may increase the loss of calcium in the urine.

Blood Pressure Medications
Taking calcium with a beta-blocker (such as atenolol), a group of medications used for the treatment of high blood pressure or heart disorders, may interfere with blood levels of both the calcium and the beta-blocker. Study results are conflicting, however. Until more is known, individuals taking atenolol, or another beta blocker, should have their blood pressure checked before and after adding calcium supplements or calcium containing antacids to their medication regimen.

Similarly, it has been reported that calcium may reverse the therapeutic effects as well as the side effects of calcium channel blockers (such as verapamil) often prescribed for the treatment of high blood pressure. These study results are also controversial. People taking verapamil or another calcium channel blocker along with calcium supplements should likely have their blood pressure checked regularly.

Cholesterol-lowering Medications
A class of medications known as bile acid sequestrants (including cholestyramine, colestipol, and colesevelam), used to treat high cholesterol, may interfere with normal calcium absorption and increase the loss of calcium in the urine. Supplementation, therefore, with calcium and vitamin D may be recommended by your healthcare provider.

Corticosteroids
Corticosteroid medications reduce the absorption of calcium, thereby increasing the risk for bone loss and osteoporosis over time. This is of particular concern for anyone who is maintained on long-term steroids.

Digoxin
High levels of calcium may increase the likelihood of a toxic reaction to digoxin, a medication used to treat irregular heart rhythms. On the other hand, low levels of calcium cause this medication to be ineffective. People who are taking digoxin should have calcium levels monitored in the blood closely.

Diuretics
Two different classes of diuretics interact with calcium in opposite ways—thiazide diuretics such as hydrochlorothiazide can raise calcium levels in the blood, while loop diuretics, such as furosemide and bumetanide, can decrease calcium levels. In addition, amiloride, a potassium-sparing diuretic, may decrease the amount of calcium excreted in the urine (and subsequently increase calcium levels in the blood), especially in people with kidney stones.

Estrogens
Estrogens may contribute to an overall increase in calcium blood levels. Taking calcium supplements together with estrogens improves gain in bone density significantly.

Gentamicin
Taking calcium during treatment with the antibiotic gentamicin may increase the potential for toxic effects on the kidneys.

Metformin
Metformin, a medication used to treat type 2 diabetes, can deplete levels of vitamin B12. Some early evidence suggests that calcium supplements may prevent or eliminate this negative effect of metformin. More research is needed.

Antibiotics, Quinolones
Calcium can interfere with the body's ability to absorb quinolone antibiotics (such as ciprofloxacin, levofloxacin, norfloxacin, and ofloxacin). If taking calcium containing supplements or antacids, therefore, you should take them two to four hours before or after taking quinolone antibiotics.

Seizure Medications
Low levels of calcium have been reported with high doses of seizure medications, such as phenytoin, which may decrease calcium absorption. Some physicians recommend vitamin D along with anti-seizure drugs to try to prevent the development of low calcium levels.

Tetracyclines
Calcium can interfere with the body's ability to absorb tetracycline medications (including doxycycline, minocycline, and tetracycline) and, therefore, diminish their effectiveness. Calcium containing supplements and antacids should be taken at least two hours before or after taking these drugs.

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