Calcium carbonate and calcium citrate are the two most common types of calcium contained in supplements, according to the National Institutes of Health Office of Dietary Supplements. Of the two, calcium carbonate is more commonly available and is both inexpensive and convenient. Supplements only work as well as the body is able to use them, and the degree and efficiency of absorption of calcium supplements is important to note.
Absorption
Both calcium carbonate and calcium citrate have similar absorption. Calcium is best absorbed in an acidic environment, according to Health Castle, the largest online nutrition community run by registered dietitians. For this reason, individuals with reduced levels of stomach acid will absorb calcium citrate, which is acidic, more easily, says the Office of Dietary Supplements. It is important to note that calcium carbonate is best absorbed with food, while calcium citrate is absorbed equally well with or without food.
Acid and Base
Calcium citrate is an acidic supplement, while calcium carbonate is alkaline, or basic, says Health Castle. Because calcium carbonate is alkaline, it is best taken with food or a glass of acidic juice, like orange juice. For better absorption, more stomach acid is needed, according to Health Castle. Calcium citrate does not require extra stomach acid to maximize its absorption because it is acidic in nature, and it can be taken with or without food for this reason.
Elemental Calcium
By weight, calcium carbonate contains 40 percent elemental calcium, and calcium citrate contains 21 percent elemental calcium. It is the amount of elemental calcium consumed at one time that determines the percentage of calcium that is absorbed, says the Office of Dietary Supplements. As the total amount of elemental calcium increases, the absorption of calcium decreases. The best absorption occurs at doses of less than 500mg, according to the Office of Dietary Supplements, which recommends, for someone who takes 1,000mg per day, taking 500mg at two different times during the day.
Other Differences
Since calcium citrate generally provides less elemental calcium per pill than calcium carbonate, more pills per day may be necessary, says the Office of Dietary Supplements. Furthermore, calcium citrate should be avoided if an individual suffers from acid stomach, reflux or ulcers. Calcium citrate supplements are normally manufactured in small capsule form. Calcium carbonate is usually manufactured in large tablets, which may be more difficult for some people to swallow. However, because it provides more elemental calcium, fewer pills may need to be consumed, according to the Office of Dietary Supplements.
Side Effects
Unfortunately, the Office of Dietary Supplements says, side effects of calcium supplementation can include gas, constipation, bloating or a combination. However, these side effects can often be nullified by spreading out the consumption of calcium supplements throughout the day, consuming food with the supplements or even changing the supplement brand used.
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