Because of potential side effects with high amounts of calcium, an upper limit of 2,500 mg is recommended.
Forms of Calcium Supplements. Calcium supplements exist in different compounds, such as calcium carbonate (Caltrate, Os-Cal, Tums), calcium citrate (Citracal), calcium gluconate, and calcium lactate. Although all of these provide calcium, they have different calcium concentrations, absorption capabilities, and other actions. Their value in preserving bones depends on many different factors:
- Calcium Concentrations. Forty percent of calcium carbonate is actually calcium, whereas calcium citrate is 24% calcium, and calcium gluconate is only 9% calcium.
- Calcium Absorption Capabilities. The calcium must also be absorbed from the stomach into the bloodstream. Calcium citrate is better absorbed than many other calcium compounds. It was reported to be the first calcium supplement to preserve bone density after menopause. (Calcium citrate also increases iron absorption. Milk and other calcium compounds tend to reduce iron absorption.) One simple method for testing the absorbency of a particular brand of calcium tablet is to place it in a glass of white vinegar at full strength and check to be sure that it breaks up within 30 minutes. Taking large amounts of antacids can impair calcium absorption. Supplements should be taken after meals.
Side Effects. Calcium supplements, even at normal doses of about 1,000 mg a day, can increase the risk for kidney stones. People should be careful not to exceed the upper limit of 2,500 mg per day. (Because many commercial foods are now fortified with calcium, this upper limit may be easier to reach than people think.) Calcium may boost the effects of drugs used to treat osteoporosis.
 | Click the icon to see an image of kidney stones. |
Although not a specific side effect of calcium, there has been much public concern about reports of a small amount of lead in calcium supplements. Although exposure to high levels of lead can cause health problems, the amount in such supplements is very small, and experts believe the amount poses no hazard.
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