What Is the Difference Between Calcium Citrate and Calcium Carbonate?

Updated on February 28, 2018
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Jon has a Ph.D in chemistry. Living an active outdoor lifestyle, he also has an interest in nutrition science and nature conservation.

Should I Supplement With Calcium Citrate or Calcium Carbonate?

If you are reading this I assume that you have decided to start supplementing your diet with calcium and are wondering which form of calcium supplements you should choose. Calcium carbonate and calcium citrate are both common and mostly safe products for oral supplementation. There are however some subtle differences which are not so obvious. So what is the difference between calcium citrate and calcium carbonate when used as a dietary supplement?

Let's start by briefly discussing the properties of each form and then compare them with regard to bioavailability and digestive comfort.

Should I use calcium carbonate or calcium citrate? Or maybe just not at all?
Should I use calcium carbonate or calcium citrate? Or maybe just not at all? | Source

What Is Calcium Citrate?

Calcium citrate is a form of calcium that is composed of calcium ions (Ca2+) and citrate ions which is an ionized version of citric acid. The formula for citrate is C6H5O73− and the chemical formula of calcium citrate is Ca3(C6H5O7)2.

While calcium citrate can be found in nature, it is most often produced industrially by combining citric acid with calcium hydroxide, which then precipitates solid calcium citrate. This calcium citrate is then pressed into pills or encapsulated as a dietary supplement.

When digested, the citrate group reverts back to citric acid in the stomach, leaving the calcium ions to be absorbed in the digestive tracts.

Citric acid is a safe and harmless compound in suitable concentrations. It is found in nature in all citrus fruits, even in somewhat high concentrations. The dry weight of lemons, for example, is about 8% citric acid and there are about 47 g/L in the liquid juice.

Citric acid is also an intermediary of the citric acid cycle, an important biochemical mechanism which occurs in all organisms that require oxygen for life and growth.

Calcium supplements in pill form. Typically sold as 500mg of calcium carbonate or 1000mg calcium citrate capsules.
Calcium supplements in pill form. Typically sold as 500mg of calcium carbonate or 1000mg calcium citrate capsules. | Source

What Is Calcium Carbonate?

Calcium carbonate is the most common naturally occurring form of calcium minerals. The main component of limestone, calcium carbonate is produced in massive quantities by mining limestone and then industrially extracting the calcium carbonate from the limestone. This calcium carbonate is then pressed into pills or encapsulated as a dietary supplement.

Calcium carbonate is composed of a calcium ion (Ca2+) and a carbonate ion (CO32-). When digested, the carbonate group reacts with stomach acid, turning into water and carbon dioxide, leaving the calcium ion behind to be absorbed in the digestive tracts.

Calcium carbonate is also the most used calcium dietary supplement due to its ready availability and price.

Raw calcium carbonate powder. Ready to be encapsulated as a mineral supplement.
Raw calcium carbonate powder. Ready to be encapsulated as a mineral supplement. | Source

Comparing the Bioavailability of Calcium Citrate and Calcium Carbonate.

The bioavailability of calcium carbonate and calcium citrate, is about the same, while calcium carbonate is a cheaper choice. However, bioavailability is typically calculated from equal amounts of calcium digested. Since calcium citrate has a lower mass percentage of calcium then calcium carbonate you will need up to twice the weight of calcium citrate to get the same amount of calcium as opposed to calcium carbonate.

Also, calcium carbonate acts as a base in the acidic stomach fluids and can neutralize them to some extent, while calcium citrate has no effect on the stomachs acidity levels.

This neutralization property of calcium carbonate can cause some acid reflux and discomfort. As such, people with delicate stomachs or problems with stomach acid could feel some discomfort if supplementing with calcium carbonate and between these two choices should choose to use calcium citrate.

However, another form of calcium which is extracted from red algae has been shown scientifically to be superior to other forms of calcium minerals in regards to bioavailability and overall benefits.

Unfortunately, red algae calcium can have a similar effect on stomach acid as calcium carbonate. But, if red algae calcium is taken with food, it should alleviate such discomfort to some extent if not altogether.

The dietary supplementation industry is massive, but is it really necessary?
The dietary supplementation industry is massive, but is it really necessary? | Source

Some Final Thoughts.

Having explained the main differences of these mineral supplements you should also consider if you really need calcium supplementation. Large groups of people are supplementing with minerals without there being a true need for them. And in some cases, this can cause them health problems down the line.

Now if you are suffering from osteoporosis or some form of chronic calcium deficiency then calcium supplementation is most likely both useful and necessary. If there is, on the other hand, no immediate medical reason to supplement with calcium it is probably best to simply eat more broccoli or some other vegetable which is rich in calcium or just drink milk.

In the end, you should at least discuss it with your doctor or some medical professional. Significant calcium supplementation has been shown to have some detrimental effects, such as increased risk of heart attack to name something, it is, therefore, reasonable to seek advice.

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

Questions & Answers

  • Which is better for osteopenia, citrate or carbonate?

    Of the two I would say citrate, although calcium from an algae source is probably best for you.

    But you should really speak to your doctor about that.

  • My blood test shows that I have low calcium. I am seventy-one. Do I take calcium citrate or carbonate?

    In your case, I would recommend the citrate version as calcium carbonate has been shown to increase the risk of heart complications. But you should really ask your doctor first.

© 2018 Jon Sigurdsson

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