Calcium: An Essential Mineral

JULY 01, 2005
Stefanie Ferreri, PharmD, CDE

Calcium is essential for many body functions. It helps regulate the heartbeat, sends nerve impulses, helps clot blood, and stimulates hormone secretions. Calcium also is essential for building denser, stronger bones in early life, and for slowing the rate of bone loss in later life. Adequate calcium intake is important because the human body cannot produce calcium. The body loses calcium every day through the shedding of skin, nails, and hair, as well as through sweating and through urine and feces. This lost calcium must be replaced. When the diet does not contain enough calcium to perform the necessary activities, calcium is taken from the bones, where it is stored.

The National Osteoporosis Foundation recommends a daily calcium intake for adults of 1000 to 1200 mg. Food is the best source of calcium; however, most Americans do not have enough calcium in their diets. Fortunately, calcium-fortified foods and calcium supplements can fill the gap, ensuring that the daily requirement is met. The amount needed from a supplement depends on how much calcium is consumed from food sources.

Sources of Calcium

One way to increase the amount of calcium in one's diet is to eat calcium-rich foods such as broccoli and low-fat milk and cheese. Foods such as orange juice, cereals, and breakfast bars have calcium added to them, so it is easier than ever to consume the recommended level of calcium for every age group. Calcium-rich, lactose-free products and lactase enzyme pills are available for those unable to consume dairy products.

Still, surveys show that many Americans are not consuming enough calcium. Many women, in fact, consume less than half of the daily recommended amount of calcium. Different types of calcium and a variety of supplements are available. Patients can easily be confused by the large amount of misinformation concerning calcium intake and supplementation.

Pharmacists need to consider special populations that need calcium supplementation (Table 1). Also, certain medications can place patients at risk for loss of bone mass (Table 2). Pharmacists can play an important role in providing useful information to their patients regarding calcium supplementation, particularly to those at risk for calcium deficiency.

How to Take Calcium

The body can best handle about 500 mg of calcium at any one time, whether from food or supplements. Therefore, calcium-rich foods and/or supplements should be consumed in smaller doses throughout the day, preferably with a meal. Because the body requires calcium 24 hours a day, some experts suggest consuming a calcium-rich food or a calcium supplement at bedtime to provide a calcium source during the night.

Calcium Interactions

Several substances can interfere with the body's ability to use calcium. Some of the most common offenders are foods high in oxalates, phytates, protein, and sodium. Foods high in oxalates include spinach, rhubarb, and almonds. Legumes?such as pinto beans, navy beans, and peas?are high in phytates. The phytate level in legumes can be reduced by soaking them in water for several hours, discarding the water, and then cooking them in fresh water. Wheat bran also is high in phytates and is the only fiberrich food that appears to reduce calcium absorption. The fiber in fruits, vegetables, and common cereals does not significantly interfere with calcium absorption. To get the maximum benefit from calcium-rich foods, they should not be eaten at the same time as foods high in oxalates and phytates, but rather 1 hour before or 2 hours after.

Excessive protein and sodium intake can increase calcium loss through the kidneys. In fact, an individual's daily calcium requirement increases in direct proportion to the amount of protein and sodium in the diet.

Vitamin D

Vitamin D plays a major role in calcium absorption and bone health. It works in the kidneys to help reabsorb calcium that otherwise would be excreted. Vitamin D is manufactured in the skin following direct exposure to sunlight. Usually 10 to 15 minutes of exposure of hands, arms, and face 2 to 3 times a week is enough to satisfy the body's vitamin D requirement. Skin color affects vitamin D production; the fairer the person is, the more he or she makes. People who are housebound and experience no sunlight exposure are unable to make vitamin D.

Experts recommend a daily intake of between 400 and 800 international units of vitamin D. Massive doses may be harmful.

Calcium Supplements

Several different calcium formulations are used in supplements, including calcium carbonate, calcium phosphate, and calcium citrate. These formulations contain different amounts of elemental calcium. It is important to read the label carefully to determine how much elemental calcium is in the supplement and how many doses to take.

Many people ask which calcium supplement they should take. The "best" supplement is the one that meets an individual's needs, based on tolerance, convenience, cost, and availability. In choosing a calcium supplement, the most important considerations are purity, absorbability, and tolerance.


Patients should choose calcium supplements with known brand names that have proven reliability. They should avoid calcium from unrefined oyster shell, bone meal, or dolomite, because these forms historically have contained higher levels of lead or other toxic metals. They should look for labels that state "purified"or have the United States Pharmacopeia (USP) symbol. Products with the USP symbol have met voluntary quality standards of purity and dissolution. These products are less likely to contain harmful contaminants and are more likely to disintegrate in the stomach.


Most brand name calcium products are absorbed easily in the body. If the product information does not state that it is absorbable, one can place the tablet in a small amount of warm water or vinegar for 30 minutes, stirring it occasionally. If it has not dissolved within this time, it probably will not dissolve in the stomach. Chewable and liquid calcium supplements dissolve well because they are broken down before they enter the stomach. The calcium in supplements needs to be easily absorbed by the body. Calcium carbonate is absorbed best when taken with food, for example, whereas calcium citrate can be taken anytime.


Whereas calcium supplements generally are a satisfactory option, certain preparations may cause side effects, such as gas or constipation, in some individuals. If simple measures such as increased fluids and fiber intake do not solve the problem, another form of calcium should be tried. Also, it is important to increase supplement intake gradually; one should take 500 mg a day for a week and then add more calcium slowly, if needed.

Calcium Interactions

Calcium supplements can cause drug-drug interactions between prescription and OTC medications. For example, calcium supplements may reduce the absorption of the antibiotic tetracycline. Calcium also interferes with iron absorption, so a calcium supplement should not be taken at the same time as an iron supplement. The exception to this "rule"is when the iron supplement is taken with vitamin C or calcium citrate. Any medication to be taken on an empty stomach should not be taken with calcium supplements.

Combination Products

Calcium supplements are available in combination with vitamins and other minerals. Although vitamin D is necessary for the absorption of calcium, it does not have to be in the calcium supplement. Minerals such as magnesium and phosphorus also are important, but they usually are obtained through food or multivitamins. Most experts recommend that nutrients come from a balanced diet, with multivitamins used to supplement dietary deficiencies.

Key Counseling Points for Patients

  • Patients should avoid consuming more than 500 mg of elemental calcium at one time (small amounts taken throughout the day are more effective)
  • Calcium carbonate should be taken with food because it needs acid production to help with absorption; therefore, patients on histamine2 receptor antagonists or proton pump inhibitors should use calcium citrate instead
  • Patients should avoid taking more than 2000 mg daily to diminish potential adverse effects
  • Iron and calcium supplements should not be taken at the same time to avoid the potential interaction that blocks absorption
  • Patients should drink plenty of fluids (6-8 glasses a day) to reduce the risk of kidney stones

Dr. Ferreri is a clinical assistant professor at the University of North Carolina at Chapel Hill School of Pharmacy.


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