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What You Need To Know About Calcium Absorption And Osteoporosis

Calcium absorption is an important consideration when selecting a supplement for an osteoporosis treatment program.

Supplements of 500 mg. should be spaced 4-6 hours apart because our bodies cannot absorb more than this at one time.

Calcium carbonate is absorbed as well as calcium citrate when taken with meals.

Calcium absorption is crucial to any treatment program for it to be effective. The body absorbing too much or too little can lead to problems.

Absorbing Calcium Effectively

The effectiveness of any given source of calcium in osteoporosis treatment depends upon a number of factors, like elemental calcium, solubility and absorption.

Elemental Calcium

Elemental calcium is the amount of calcium available to your body for absorption. Normally, this is the total amount of calcium listed on the label under the Nutrition Facts panel.

This is quite different than the weight of each tablet-which is the weight of the calcium plus whatever it's bound to, such as carbonate, citrate, lactate or gluconate.

A greater percentage of elemental calcium means that fewer tablets are needed to achieve the desired calcium intake. For instance, elemental calcium accounts for 40% of a compound in the calcium carbonate form but only 24% in the calcium citrate form.


Solubility refers to the amount of calcium that can be dissolved in water at a neutral pH. In other words, if stomach acid levels are high, most forms of calcium are soluble, depending on the calcium source.


Calcium absorption varies with the source of calcium as well as how much calcium is consumed at one time. As the body can only absorb 500 mg of elemental calcium at one time, it is best to take supplements three times during the day with 4 to 6 hours between doses.

Toxicity may only occur with doses over 2,500 milligrams of elemental calcium per day. It is also important to consider the impact of other medications and supplements when timing your calcium intake.

Calcium citrate and calcium carbonate have similar absorption if calcium carbonate is taken with meals.

Calcium absorption varies significantly depending on how it is formulated. Supplements providing 500 mg. of elemental calcium will provide calcium absorption as follows:

  • Calcium Citrate/Malate (CCM)
    • absorption rate 40%
    • calcium absorbed 200 mg
  • Calcium Carbonate
    • absorption rate 26%
    • calcium absorbed 130 mg
  • Calcium Citrate
    • absorption rate 22%
    • calcium absorbed 120 mg

Some research suggests that calcium bisglycinate and calcium formate have even higher absorption rates than CCM. These forms of calcium are found in leafy green vegetables and food based supplements such as Greens + Bone Builder.

Absorption rates for calcium carbonate and calcium citrate are similar if taken with meals, while calcium lactate (from cow's milk) and calcium gluconate (highly promoted in liquid formulation) have solubility less than calcium citrate.

Stomach acidity also plays a role in calcium absorption. According to Dr. Michael Murray in the book, Encyclopedia of Nutritional Supplements, studies show that 40% of postmenopausal women are severely deficient in stomach acid.

Dr. Murray argues that people with insufficient stomach acid can only absorb about 4% of calcium carbonate versus 22% in people with normal stomach acid.

Low calcium absorption may lead to calcium deposits in the arteries and joints, high blood pressure, kidney stones and fractures... as well as osteoporosis.

Some people also experience bloating and nausea when they take calcium supplements. There are a number of strategies for preventing this discomfort.

Calcium Overdose? As a guideline, it is recommended that consumption not exceed 2,500 mg of calcium a day. Excess calcium intake can lead to constipation and an increased risk of developing calcium kidney stones. It may also inhibit the absorption of iron and zinc.

Vitamin D Is Essential For Absorption

Osteoporosis Canada reports that vitamin D3 can increase calcium absorption by as much as 30 to 80 percent. The U.S. National Osteoporosis Society recommends daily intake of 800-1,000 IU but other experts recommend a much higher vitamin D dosage for optimal bone health including 5,000 IU for people living in northern regions.

For less than $30 a year, Puritan's Pride Bone Care provides a formula of calcium, magnesium, vitamin D and vitamin K that optimizes calcium absorption... while meeting recommended daily intake (RDI) for each element.