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Understanding Different Types of Calcium: Part One

Ensuring that you are taking the best form of calcium for your body will not only benefit your bones, but will also save you from spending money on a type of calcium supplement that is not going to work well for you or which may provide little value to your body. With so many forms of calcium on the market, choosing one can be complicated indeed. Certain types of calcium supplements may be better for some types of people than others. Some of the most common forms of calcium supplements that are available include: calcium carbonate, oyster shell calcium, calcium gluconate, calcium citrate, calcium citrate-malate, calcium hydroxyapatite, calcium lactobionate, and others. But there is more to choosing the right calcium supplement than just choosing the right form of calcium. Be sure to keep the following factors in mind when choosing a calcium supplement that’s right for you.

Determining Elemental Calcium Content

Calcium supplements always come as a salt or a chelate, meaning they are attached to a carrier compound. Elemental calcium refers to the actual amount of calcium in the supplement. The Supplement facts panel on a calcium supplement is useful for determining how much calcium a serving actually contains. Be aware of the serving size when calculating the amount of calcium that is in one serving. Also, paying attention to how it’s displayed is important. Below are some examples to help you understand how much calcium is in your supplement. (These same rules can be applied to other minerals as well.) The examples below use calcium citrate, which is about 20% calcium.

If the label states the amount of elemental calcium per serving or per capsule, then there’s no guessing.
Calcium citrate (providing 200 mg elemental calcium) 1000 mg

If the label states that one capsule or one serving provides 1000 mg of calcium citrate, then you can assume that one capsule or serving only provides 200 mg of calcium.
Calcium citrate 1000 mg

If the label states that one capsule or one serving provides 1000 mg of calcium from calcium citrate (using words or parentheses to indicate the source), then you know that you are getting 1000 mg of calcium in that serving.
Calcium (citrate) 1000 mg

Solubility and Bioavailability

At one time it was believed that the better a substance dissolved in water, the more absorbable it was by the body, and therefore more bioavailable. This is often the case, but not always. Several older studies from 1987 and 1990 measured both the solubility in water as well as absorption in humans of various forms of calcium. They found that low water solubility didn’t always translate into low absorption in the body. The authors thought that this could be due to the added stomach acid. However, there are of course numerous other variables in the human digestive tract including enzymes, bile salts, etc. In addition, a recent study found that calcium forms that yield higher blood levels of calcium (better bioavailability) don’t necessarily have better bone-building effects than those than yield lower blood levels of calcium.

Factors Affecting Calcium Absorption

Even if you’re getting the right type and amount of calcium, there are other factors at work that you should be aware of. If you’re deficient in vitamin D, you’ll only absorb 10% of your calcium instead of the average 30%. In addition, deficiencies in other vitamins, minerals and trace minerals like vitamin K, magnesium, zinc, copper, manganese, strontium and boron among others can contribute to poor bone health. In one study, women who were supplementing with calcium citrate-malate along with trace minerals zinc, copper and manganese experienced positive bone-building effects, while the women taking just calcium or just trace minerals continued to lose bone. Regular weight-bearing exercise also helps your body to better use the minerals and the calcium that you consume to stimulate bone growth.
Taking too much calcium will actually cause you to absorb less of it. It’s the body’s natural way of protecting itself. Take no more than 500 mg calcium at once. Excessive sodium, caffeine and alcohol intake can increase calcium loss, so it’s important to replace the calcium (and other minerals) you might be losing in these cases. People living in areas with high levels of calcium in the drinking water, or people who consume more calcium from their diet, may not need to supplement as much calcium. Oxalate and phytate compounds found in certain vegetables and grains reduce calcium absorption. If you’re trying to get your calcium from vegetables in a non-dairy, non-supplemented diet, you may have to consume a lot more calcium from food than you would from milk or from a supplement.

That’s enough info for one sitting. Stay tuned for part 2 where we will examine the different forms of calcium used in calcium supplements and discover what’s what and what’s best!


Andon MB et al. Supplementation trials with calcium citrate malate: evidence in favor of increasing the calcium RDA during childhood and adolescence. J Nutr. 1994;124(8 Suppl):1412S-1417S.

Bristow SM et al. Acute and 3-month effects of microcrystalline hydroxyapatite, calcium citrate and calcium carbonate on serum calcium and markers of bone turnover: a randomised controlled trial in postmenopausal women. Br J Nutr. 2014 Nov 28;112(10):1611-20.
Castelo-Branco C et al. Efficacy of ossein-hydroxyapatite complex compared with calcium carbonate to prevent bone loss: a meta-analysis. Menopause. 2009 Sep-Oct;16(5):984-91.
Castelo-Branco C & Dávila Guardia J. Use of ossein-hydroxyapatite complex in the prevention of bone loss: a review. Climacteric. 2015 Feb;18(1):29-37.
Ciria-Recasens M et al. Comparison of the effects of ossein-hydroxyapatite complex and calcium carbonate on bone metabolism in women with senile osteoporosis: a randomized, open-label, parallel-group, controlled, prospective study. Clin Drug Investig. 2011 Dec 1;31(12):817-24.
Dairy Research Institute. Calcium Bioavailability 2011: Scientific Status Report.
Dawson-Hughes B et al. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med. 1997;337(10):670-6.
Dawson-Hughes B et al. Rates of bone loss in postmenopausal women randomly assigned to one of two dosages of vitamin D. Am J Clin Nutr. 1995;61(5):1140-5.
Dawson-Hughes B et al. A controlled trial of the effect of calcium supplementation on bone density in postmenopausal women. N Engl J Med. 1990;323(13):878-83

Dawson-Hughes B and Harris SS. Calcium intake influences the association of protein intake with rates of bone loss in elderly men and women. Am J Clin Nutr. 2002 Apr;75(4):773-9.

Fernandez-Pareja A et al. Prevention of Osteoporosis: Four-Year Follow-Up of a Cohort of Postmenopausal Women Treated with an Ossein-Hydroxyapatite Compound. Clinical Drug Investigation. 2007; 27(4):227-232.
Garriguet D. Component of Statistics Canada Catalogue no. 82-003-X Health Reports. Bone health: Osteoporosis, calcium and vitamin D. July 2011
Johnston CC et al. Calcium supplementation and increases in bone mineral density in children. N Engl J Med. 1992; 327(2):82-7.

Kressel G. “Bioavailability and Solubility of Different Calcium-Salts as a Basis for Calcium Enrichment of Beverages,” Food and Nutrition Sciences, Vol. 1 No. 2, 2010, pp. 53-58.
Lloyd T et al. Calcium supplementation and bone mineral density in adolescent girls. JAMA. 1993; 270(7):841-4.

Michaelsson K et-al “Long term calcium intake and rates of all … based prospective longitudinal cohort study” BMJ. 2013; 346: 1-13

Patrick L. Comparative absorption of calcium sources and calcium citrate malate for the prevention of osteoporosis. Altern Med Rev. 1999 Apr;4(2):74-85.
Peacock M et al. Effect of calcium or 25OH vitamin D3 dietary supplementation on bone loss at the hip in men and women over the age of 60. J Clin Endocrinol Metab. 2000;85(9):3011-9.
Saltman PD & Strause LG. The role of trace minerals in osteoporosis. J Am Coll Nutr. 1993 Aug;12(4):384-9.
Sakhaee K et al. Meta-analysis of calcium bioavailability: a comparison of calcium citrate with calcium carbonate. Am J Ther. 1999 Nov;6(6):313-21.
Sheikh MS et al. Gastrointestinal absorption of calcium from milk and calcium salts. N Engl J Med. 1987 Aug 27;317(9):532-6.
Straub, D. A. “Calcium Supplementation in Clinical Practice: A Review of Forms, Doses, and Indications”. Nutrition in Clinical Practice. 2007; 22 (3): 286–96.
Strause L et al. Spinal bone loss in postmenopausal women supplemented with calcium and trace minerals. J Nutr. 1994;124(7):1060-4.

Ueda Y & Taira Z. Effect of anions or foods on absolute bioavailability of calcium from calcium salts in mice by pharmacokinetics. J Exp Pharm 2013:5 65-71.

Unitika Ltd. Effect of Lactose Fermented Product Containing Lactobionic Acid, Produced by Acetic Acid Bacteria on Calcium Absorption in Humans. 2010.
Weaver, CM et al. “Absorption of Calcium Fumarate Salts Is Equivalent to Other Calcium Salts When Measured in the Rat Model”. Journal of Agricultural and Food Chemistry. 2002; 50 (17): 4974–5.

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