By the way, doctor: Which calcium supplement should I take?
Q Which calcium supplement is better for older women, calcium citrate or calcium carbonate?
A Calcium citrate (Citracal) is probably the better choice for older people. Although calcium carbonate is less expensive — it contains a higher percentage by weight of actual (elemental) calcium — it requires stomach acid for absorption. That means taking it with or soon after a meal. By contrast, calcium citrate is readily absorbed, with or without stomach acid. The distinction may be important if you have achlorhydria, or low stomach acid, which is associated with a variety of age-related conditions. Many calcium carbonate supplements are also poorly soluble, although this problem can be avoided by taking chewable preparations such as Tums or Viactiv.
The recommended daily intake of calcium for postmenopausal women is 1,200 mg (plus 400–600 IU/day of vitamin D, which aids calcium absorption by the intestine). The body can't assimilate more than about 500 mg of calcium at a time, so take your calcium in small doses throughout the day.