It's not enough to scarf down a few glasses of milk at once or half a block of cheese and then not worry about your calcium intake for the rest of the day. You can only absorb so much calcium, an essential mineral obtainable only through diet, at one time under the best of circumstances. A number of dietary factors can also decrease the amount of calcium absorbed.
Maximum Absorption
Adults over age 19 need 1,000 mg per day up to age 51 for women and age 70 for men, when your needs increase to 1,200 mg per day. But don't pop a 1,000 mg supplement hoping to fulfill your calcium needs in one pill. Your body absorbs calcium best when you take no more than 0.5 g or 500 mg at one time. The more calcium you ingest at one time, the less your body absorbs.
Calcium Types
Calcium supplements supply differing amounts of elemental, or pure, calcium, depending on what other substances they're bound to. The most common types of calcium supplements are calcium citrate and calcium carbonate. Calcium citrate supplements contain 40 percent elemental calcium, while calcium carbonate supplies 21 percent elemental calcium, according to the Office of Dietary Supplements. When you look at calcium supplements, look at the amount of elemental calcium in them, not the amount of the total compound, to determine how much of the supplement you can absorb at once.
Interfering Factors
If you don't get enough vitamin D, you don't absorb calcium in the intestines well. Caffeine, alcohol, sodium and oxalic acid in some vegetables, such as spinach, rhubarb and collard greens, decrease calcium absorption. Every gram of sodium you take in decreases calcium absorption by 5 to 10 mg, registered dietitian Reed Mangels, Ph.D. explains. If you ingest these substances at the same time as calcium, increase your calcium intake to offset the increased loss. Since you absorb calcium in the lower intestine, disorders that cause malabsorption of nutrients also decrease the amount of calcium you absorb.
Considerations
If you follow a vegetarian diet, you may have a harder time getting the maximum amount of calcium because vegetarians eat more vegetables that can interfere with calcium absorption and consume little or no dairy. If you take calcium supplements, divide the doses so that you take no more than 500 mg at a time for maximum absorption.
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