Understanding Different Types of Calcium: Part 1

Published on March 02, 2015 by Justine Florence

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.

1. 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

2. 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.

3. 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!

Image by © 2011 Kalinovsky Dmitry via DollarPhotoClub


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  • Mom!

    Great & useful info - the 2nd blog should help to define the varying types better........

  • BritWit82

    I take 600mg of elemental calcium once a day. Is this still effective?

    If my calcium is combined with D and K will this help me absorb more than 500mg at a time?

    Also what happens to the Calcium that is not absorbed?

    • Justine Florence

      Hi Brit, thanks for your questions. If you are taking 600 mg at once, you likely won’t absorb all of it, but you will probably absorb a good chunk.

      Taking vitamins D and K at the same time as your calcium probably won't necessarily help you absorb more than 500 mg at once. The body has built-in mechanisms that try to protect it from absorbing more than it needs, so the body may down-regulate its calcium receptors to prevent it from absorbing too much at once, which is why taking too much can actually inhibit its absorption. Vitamins D & K will help you to absorb and use calcium effectively, but only up to a certain point. In addition, since vitamins D & K are fat-soluble, they take some time to work in the body, so taking them at the same time doesn’t necessarily make a difference. Taking them in the same day, however, is important.

      Excess calcium that is absorbed but not used may circulate in the blood stream before being excreted. Excess calcium that can’t be absorbed will be excreted in the urine or stool.

  • Marina

    Thank you for the useful information.
    Which factors determine, if excessive calcium is going to be excreted from the body or accumulated in the soft tissues and arteries?

    • Colin O'Brien

      Hi Marina,

      This is a very good question and a very complicated one. There are many factors that contribute to the fate of calcium within our body but here are a few of the most important determinants of arterial calcification:

      1. Vitamin K2 deficiency: K2 is necessary for turning on or activating Matrix GLA protein (which prevents arterial calcification) and also activating osteocalcin which acts to stimulate calcium uptake into bone and form new bone. K2 essentially acts a guiding system for calcium away from the cardioavscular system and toward the bone.
      2. Magnesium deficiency: Magnesium and calcium act to counterbalance one another, and so, in the case of excess calcium relative to magnesium, there is evidence showing that this may lead to excess buildup of calcium in the body and arteries.
      3. Underlying disease: Conditions such as diabetes and kidney disease can predispose you to arterial calcification because you are unable to properly excrete excess calcium from the body. Additionally, imbalances in acidity levels and inflammation within the body can aggravate the calcification process. For example, if there’s pre-existing arterial inflammation, which most of us already have to some degree due to diet and lifestyle, calcium is included in the scarring or atherosclerosis process.

      I hope this helps to answer your question and concerns.

  • BritWit82

    I read that excess calcium can build up in the arteries. Would an extra 100 mg/day increase my risk for heart disease?

    • Colin O'Brien

      Hi Brit,

      To start, please see the comment below in regard to Marina's question.

      100mg/day of extra calcium generally is a very low amount and so would not have a significant impact on heart disease or arterial calcification. Additionally, there is an abundance of research that fails to show a connection between calcium supplements and heart disease, contrary to previous correlations made and much media hype.

      All in all, it depends on what your baseline intake is in the first place and other health factors such as other nutrient deficiencies and predisposing diseases.

  • Cami

    That's cleared my thoughts. Thanks for cobuirntting.