Calcium Supplements: Benefits and Risks

W. Steven Pray, PhD, DPh; Joshua J. Pray, PharmD candidate


US Pharmacist. 2004;29(12) 

Virtually all people should take steps to prevent the developement of osteoporosis. It is the most frequently occurring bone disease in the United States, affecting 55% of those ages 50 and older.[1,2] The morbidity it causes is devastating for elderly patients. Ths U.S. will experience an epidemic of osteoporosis in coming decades as baby boomers reach the ages of highest risk.[3]

The Epidemiology of Osteoporosis

Osteoporosis is usually thought of as a disease of elderly females. The National Osteoporosis Foundation (NOF) estimates that eight million American women have been diagnosed with osteoporosis;[2] however, the NOF also estimates that two million men have the condition. Women are at greater risk because they have a lower peak bone mass due to smaller stature and also because they experience a rapid postmenopausal bone loss.[3]

No ethnic group is spared from its ravages, although the percentages of those affected vary. In women older than 50, osteoporosis affects 5% of blacks, 10% of Hispanics, and 20% of whites and Asians.[2] Low bone mass affects 35% of black women older than 50, 49% of Hispanics, and 52% of whites and Asians. For men over the age of 50, osteoporosis affects 3% of Hispanics, 4% of blacks, and 7% of whites and Asians. Low bone mass is found in 23% of Hispanic men older than 50, 19% of blacks, and 35% of whites and Asians. The Asian subpopulation has the lowest calcium intake of any ethnicity.[4]

Morbidity Associated With Osteoporosis

Osteoporitic fractures are the most obvious problem associated with osteoporosis. One half of women and one fourth of men over age 50 will experience an osteoporosis-related fracture.[2] The national toll is about 700,000 vertebral fractures, over 300,000 hip fractures, and 550,000 additional fractures yearly.[2] The consequences of fracture can be devastating. One fourth of those over 50 die the year after a hip fracture; one fourth who were ambulatory before a hip fracture are forced into long-term care.[2]

Once a patient has experienced an osteoporotic fracture, the risk increases for further fractures. If a patient older than 65 experiences a vertebral fracture, the risk of a femur or hip fracture within five years is 6.7% and 13.3%, respectively.[1] Further, once the first vertebral fracture has occurred, the risk of another vertebral fracture increases by four to seven times.[1]

Risk Factors for Osteoporosis

The NOF lists 19 risk factors for osteoporosis.[2] While some cannot be modified (e.g., racial origin, age, gender, family history), others can (e.g., cigarette smoking, excessive alcohol use, inactive lifestyle). Two risk factors are simple to address: low lifetime calcium intake and vitamin D deficiency.

The Daily Suggested Calcium Intake

The body allows absorption of only about 20% to 30% of ingested calcium.[5] The National Academy of Sciences recommends a calcium intake of 1,000 to 1,200 mg/day for all adults and 1,300 mg for pregnant and lactating females ages 14 to 18.[6,7]

Unfortunately, repeated surveys reveal that most people obtain less than half of the suggested amount of calcium.[6] Other factors mitigate against obtaining adequate calcium. Caffeine, which is falsely assumed to be safe, is a major culprit in osteoporosis, since it may impair calcium absorption.[5] Ingestion of oxalates (as in chocolate and spinach), iron (as in liver and raisins), and phytates (found in whole grains) also impair calcium absorption.[5]

Calcium and Osteoporosis

Over 99% of the body's calcium is in the skeleton, where it provides mechanical rigidity.[5] When calcium intake is lower than normal, the skeleton is used as a reserve to meet needs. Long-term use of skeletal calcium to meet these needs leads to osteoporosis. Americans have a high risk of osteoporosis, since their average diet contains only 600 mg of calcium daily.[5]

Calcium Sources

Some patients have the mistaken belief that foods contain sufficient calcium to meet their needs. One source of calcium-rich foods includes the dairy group; however, many patients are lactose intolerant and avoid dairy products. Thus, they are at risk for osteoporosis. Some patients attempt to compensate by ingesting other foods that contain high levels of calcium (e.g., broccoli, Chinese cabbage [bok choy], dried figs, greens [kale, mustard, turnip], salmon, sardines with bones, and soy nuts), although it is unrealistic to suggest that these limited foods could be used as milk substitutes.[5] Thus, other patients choose fortified foods and drinks, such as breakfast bars, cereals, juices, and milk substitutes. An innovative form of calcium, calcium citrate malate combines high aqueous solubility with high bioavailability (at least 30% to 40% greater than calcium carbonate) and acceptable taste characteristics.[8] It can be found in products such as Tropicana Pure Premium orange juice. Patients should be urged to read labels to determine the amount of calcium per serving.

Calcium Supplements

For many patients, calcium supplements are the most appropriate choice for prevention of osteoporosis. Pharmacists should advise patients to take less than 500 mg of calcium at a time to maximize absorption. Calcium absorption is increased in an acidic environment, so tablets should be taken with meals (calcium citrate does not need to be taken with food). Although unconfirmed, calcium citrate is thought to be absorbed more easily than other forms of calcium.

Precautions With Calcium Supplements

Ingesting too much calcium in a misguided attempt to build skeleton may cause kidney stones, milk-alkali syndrome, or interference with iron absorption.[9,10] If a patient is at high risk of stone formation, calcium citrate may be preferred as a calcium source. One study found that calcium citrate did not increase the risk of stone formation when it was given to 18 postmenopausal women without stones.[10] Coadministration with potassium citrate reduced the risk of uric acid and calcium oxalate stones. Calcium supplementation also may lead to constipation, so patients should ingest adequate amounts of fiber (e.g., psyllium).

Lead Contamination

During the 1980s, reports emerged of lead contamination in calcium supplements made from bone meal and dolomite. An investigation of lead in calcium supplements appeared in 2000 in JAMA.[11] Researchers examined 21 formulations of calcium carbonate (both natural [i.e., oyster shell] and refined). Four out of seven natural products and four out of 14 refined products, including brand products, had measurable lead content. A research team in California found essentially the same contamination in calcium supplements.[12]

Publicity arising from this publication caused some patients to cease calcium supplement ingestion. The Internet still offers Web sites discussing the issue.[13,14,15]

A good resource for pharmacists is the National Safety Council's Web site that discusses the concerns about lead exposure, its dangers in children, and the fact that lead exposure is a lingering problem in the U.S.[16] The site also directs readers to the FDA press office for further information.

Pharmacist Advice on Calcium Supplements

Pharmacists should be aware of suggested daily intakes of calcium and encourage all patients to supplement their daily intake until they reach those goals. They should assure patients that the risk of lead toxicity is remote compared to the risk of osteoporosis.

Pharmacists should also counsel patients on the choice of an appropriate calcium supplement. If the patient ingests a multivitamin that contains 100% of the daily requirement of vitamin D, the patient must be cautioned against choosing a calcium supplement that also contains vitamin D. The pharmacist would be well advised to briefly describe the fat-soluble nature of vitamin D and the resultant toxicity (e.g., anorexia, nausea, vomiting, polyuria, polydipsia, weakness, nervousness, pruritus, impaired renal function, azotemia). The pharmacist must then point out vitamin D free calcium supplements.

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Sidebar: Overingestion of Calcium Can Lead to Toxicity

A woman breast-feeding her first child developed vertebral fractures.[17] During a second pregnancy, she voluntarily instituted a high-calcium diet and supplemented it with calcium carbonate to avoid further fractures. Each day, she ingested three servings of milk, two of calcium-fortified orange juice, two of calcium-fortified cereal, part of a Nutri-Grain Bar, a multivitamin, one Caltrate, and one Viactiv. Her daily calcium intake was 5,036 mg during her pregnancy; her vitamin D intake was 1,200 mg. Due to hypercalcemia, she developed increased thirst, urinary frequency, nocturia, anorexia, nausea, lightheadedness, and mental confusion. Her total serum calcium was 15 mg/dL. With calcium restriction and appropriate medical intervention, her symptoms abated and her serum calcium returned to normal two weeks after discharge from the hospital.

Sidebar: Preventing Osteoporosis

There are many steps people can take to reduce the risk of osteoporosis, a devastating bone disease. While Caucasian and Asian women have the highest risk, women and men of all ethnicities may develop this disease.

Bone Mass Changes

Osteoporosis affects millions of U.S. citizens. Bone is not hard and unchanging like a rock. Instead, it is a living material that constantly changes throughout your life. As you grow, adding calcium to your skeleton gives it the strength it will need in later life.

After age 30, the bone is at risk of harm. During these later years, many people find that their bone breaks down faster than it can be rebuilt. If the breakdown is sufficiently severe, fractures begin to occur—the signs of osteoporosis. People who suffer a hip or back fracture typically begin a downward spiral of hospitalization and increasing debility.

Exercise to Prevent Osteoporosis

There are several methods that help prevent osteoporosis. One is increasing your level of exercise. Everyone knows that muscles respond to exercise by becoming stronger; however, it is not as widely known that bone also becomes stronger in response to exercise. When a person exercises, the body sends messages to the bones that make the bones become heavier. Increasing their density also increases their strength.

One type of exercise that benefits the bones is weight bearing, or working against gravity, as when the feet and legs bear weight. This includes simple exercises such as walking, climbing stairs, and dancing. The person who has engaged in little exercise should start slowly (walking rather than jogging). Further, those who have frail builds, active osteoporosis, or a history of fracture should speak to their physician before starting an exercise regimen.

Another type of exercise to strengthen the skeleton is resistance based, such as weight lifting. It is best to start with weights light enough to lift comfortably, and follow medical advice as suggested.

There are several videos and DVDs on exercises, such as yoga and pilates, that help build stronger bones.

Calcium Supplementation

Perhaps the most effective method of preventing osteoporosis is ingestion of adequate calcium. Experts suggest the daily requirement for calcium is 1,300 mg for people ages 9 to 18, 1,000 to 1,200 mg for adults 19 to 50, and 1,500 mg for people over 50. Foods that are high in calcium include milk, yogurt, cheese, tofu, sardines, and fortified orange juice. It is better not to begin heavy supplementation all at once. You may tolerate the calcium better if you begin with 500 mg daily for a week or so, increasing slowly until you take in the recommended amount. Even then, side effects of calcium are generally mild with normal dosing. Calcium can harden the feces, causing constipation. This can be minimized by drinking plenty of water and increasing dietary fiber or supplementing with a fiber product, such as one containing psyllium.

You should take only the amount of calcium recommended. Ingesting high doses of calcium each day can be harmful and can cause kidney stones. Also, many calcium supplements contain vitamin D, which is dangerous in doses above the recommended daily amounts. If you are already taking a multivitamin, consult your pharmacist for help in choosing a calcium supplement. Vitamin D overdose symptoms include appetite loss, weakness, excessive thirst and/or urination, nausea, and vomiting.

Pay Attention to Other Risk Factors

Stop smoking and avoid drinking alcohol—both increase the risk of osteoporosis. Intake of beverages that contain caffeine should be avoided or limited. Caffeine can decrease calcium absorption, and possibly lead to osteoporosis.

Remember, if you have any questions, Consult Your Pharmacist.


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