Calcium is found in many multivitamin-mineral supplements, though the amount varies by product. Dietary supplements that contain only calcium or calcium with other nutrients such as vitamin D are also available. Check the Supplement Facts label to determine the amount of calcium provided.
The two main forms of calcium dietary supplements are carbonate and citrate. Calcium carbonate is inexpensive, but is absorbed best when taken with food. Some over-the-counter antacid products, such as Tums® and Rolaids®, contain calcium carbonate. Each pill or chew provides 200–400 mg of calcium. Calcium citrate, a more expensive form of the supplement, is absorbed well on an empty or a full stomach. In addition, people with low levels of stomach acid (a condition more common in people older than 50) absorb calcium citrate more easily than calcium carbonate. Other forms of calcium in supplements and fortified foods include gluconate, lactate, and phosphate.
Calcium absorption is best when a person consumes no more than 500 mg at one time. So a person who takes 1,000 mg/day of calcium from supplements, for example, should split the dose rather than take it all at once.
Calcium supplements may cause gas, bloating, and constipation in some people. If any of these symptoms occur, try spreading out the calcium dose throughout the day, taking the supplement with meals, or changing the supplement brand or calcium form you take.
 
Linna 

Attending physician
Linna Attending physician
Dr. Linna,a Tongji University and several III grade hospitals trained specialist, received her medical degree in 2001, and has18 years of clinical experience. DrLinna is proficient in the diagnosis and treatment of commonly occurring Orthopedics and surgical diseases, such as sports injuries or trauma to the back, neck, shoulder, knee, ankle, and other joints, as well as surgical Congenital disease management. Dr. Linna’s specialist expertise includes minimally invasive surgery, Mainipulation replacement for Fracture or Dislocatio and combined with new diagnostic techniques in treating pediatric surgical diseases.