While calcium citrate and calcium carbonate can both supply the recommended intake of calcium in different doses, they do differ in a number of ways:
1. In some clinical studies, calcium citrate has been found to be more easily digested and more readily absorbed than calcium carbonate. In addition, calcium citrate is better absorbed in persons who have decreased stomach acid.
2. While both calcium citrate and calcium carbonate can cause constipation, calcium citrate is less likely to have this effect. (Note that the overall incidence of constipation is low for either form.)
3. The compound calcium carbonate contains 40 percent elemental calcium, whereas calcium citrate contains only 21 percent. To get the same amount of elemental calcium, you’d have to take more calcium citrate tablets than you would calcium carbonate.
4. Calcium citrate tends to be more expensive than calcium carbonate. And since you’d need to take more doses to get the same amount of calcium, this also raises your cost.
Regardless of the form of calcium you choose, remember that the more your doses rise above 500 mg per dose, the less calcium your body will actually absorb. Your best solution: Avoid taking more than 500 mg per dose. If your recommended daily intake is 1,000 mg, for example, divide that into at least two doses taken over the course of the day. In addition to helping the absorption issue, splitting up your daily doses can help reduce the possibility of adverse reactions, the most common of which are gas, bloating, and constipation. If spreading out the doses does not relieve side effects, try either taking your calcium supplement with meals or changing brands.