Calcium carbonate and calcium citrate are the two major forms of calcium supplements sold. Calcium is also available as a gluconate, lactate and phosphate in supplements and fortified food. Calcium is the most abundant mineral in the body and it is needed for muscle functioning, nerve transmission, hormonal secretion and intracellular signaling. However, only 1 percent of the calcium in the body is used in this process; the rest is stored in bones and teeth where it is the building block of the body's skeletal support.
The Need for Calcium Supplementation
Young children and postmenopausal women especially need more calcium than others for growth and to maintain the body's bone mass. The onset of menopause causes increased bone reabsorption and reduction in bone mass as calcium leaches from bones due to reduced estrogen production. While you can meet your daily calcium requirement from dietary sources such as milk, cheese, yogurt and fortified foods, the corresponding calorie intake is too high. Therefore, calcium supplementation is required to meet a higher daily calcium intake requirement.
Absorption of Calcium Content
Calcium citrate and calcium carbonate contain different amounts of elemental calcium. In the former, the calcium content is 21 percent, while it is 40 percent in the latter. This means that if you get the same strength of the two supplements you will need twice as many of the citrate to get the same calcium as from the carbonate. However, the extent of absorption of calcium from these two supplements is more important since it determines the quantity of calcium that is available to the body for use. While some people believe calcium citrate is more efficiently absorbed than the carbonate, there is no evidence to support this.
Scientific Evidence
A comparative study done by R.P. Heaney et al. at the Osteoporosis Research Center of Creighton University on 24 postmenopausal women determined the difference in the absorption of calcium citrate and calcium carbonate. The study found that both supplements are absorbed to the same extent and have equivalent bioavalability.
Other Factors Affecting Absorption
While the absorption of the carbonate is more efficient if the supplement is taken with food, the citrate form is absorbed to the same extent with or without food. Furthermore, the citrate is better absorbed in people with reduced levels of stomach acid. Lastly, you should take vitamin D alongside any of these calcium supplements to improve the absorption of calcium.
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