Calcium-Part 1: What kind should I take? I am confused!!!!

English: An osteoporotic elderly women in Japan.

English: An osteoporotic elderly women in Japan. (Photo credit: Wikipedia)

There are hundreds of different brands of calcium supplements and different forms of calcium.  When we are talking about calcium intake, we are actually referring to the elemental calcium, not the compound calcium. What does this mean?

Elemental Calcium vs Calcium Compound

Calcium is absorbed into our body as ionized elemental calcium (Ca 2+). This means that we need to check the amount of elemental calcium the supplement contains rather than just the amount of calcium as a compound (ie calcium carbonate, calcium citrate etc). What is important on the label is the amount of elemental calcium, not just the calcium compound. For example, a calcium compound such as calcium carbonate has 40% of elemental calcium. If the bottle says each serving has 1000mg of calcium carbonate, it may only contains 400mg of elemental calcium.  We can also check the label by looking for the RDA (Recommended Daily Amounts).  If the bottle states a serving contains 40% of the RDA of calcium, then it contains 400mg of elemental calcium per serving (RDA for most individuals is 1000mg of calcium per day). Fortunately, elemental calcium is listed in the Supplement Facts panel, so consumers do not need to calculate the amount of calcium supplied by various forms of calcium supplements.

Different types of Calcium

Calcium may exist in different forms, each form may contain different amounts of elemental calcium.  The two main forms of calcium in supplements are calcium carbonate and calcium citrate.

Calcium Compound Description
Calcium carbonate(Ca2+: about 40% calcium by weight[i])
  • most inexpensive, common and convenient
  • it’s absorption depends on stomach acid.
  • best if taken with food
  • cause more gassing, bloating, constipation (if this occurs, need to spreading out the calcium dose throughout the day and/or taking the supplement with meals)
  • study indicates that chronic use of Calcium carbonate only supplement may decrease stomach acidity over time.
  • may not be tolerated well in people with a history of stomach ulcer [ii]
alcium citrate(Ca2+: about 20% by weight)
  • more soluble, therefore excellent absorption
  • absorbed well even without food
  • great for people with achlorhydria, bowel disease or absorption disorders. [iii]
Calcium lactate(Ca2+: about 13% by weight)
  • highly soluble calcium salt and bioavailable. It is used in calcium fortification of beverages. [iv]
  • can be effective at various pHs

Other types of calcium supplements:

Oyster Shell Calcium: Due to environment pollution, some oyster shell calcium may contain lead. It’s up to the manufacture to strip away the lead from the oyster shell calcium as much as possible.

Ionized form: liquid or powder which can be dissolved in liquid is ideal.




[iii] Committee to Review Dietary Reference Intakes for Vitamin D and Calcium, Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.

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4 Responses to Calcium-Part 1: What kind should I take? I am confused!!!!

  1. Pingback: Calcium-Part 2: Where can I get my Calcium? | Ask Dr. James

  2. Pingback: Is it possible to take TOO MUCH calcium? | Ask Dr. James

  3. Pingback: Calcium Part3: What affects Calcium absorption? | Ask Dr. James

  4. Pingback: Keeping my bone strong | Ask Dr. James

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