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Calcium Salts: Citrate vs Carbonate vs Orotate & Others

Written by Carlos Tello, PhD (Molecular Biology) | Last updated:
Jonathan Ritter
Puya Yazdi
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology), Puya Yazdi, MD | Written by Carlos Tello, PhD (Molecular Biology) | Last updated:
Calcium salts

What’s the difference between calcium carbonate, orotate, citrate, and coral calcium? Do some work better than others? Read on to get a quick overview of the advantages and drawbacks of each form of calcium.

What Are Calcium Salts?

Calcium is the most abundant mineral in the human body and accounts for about 1-2% of its weight. Each and every cell – in the bones, heart, muscles, and nervous system – need it to function properly [1, 2].

Like most earth metals, calcium naturally builds various salts. Let’s dive into basic chemistry for a moment to understand why.

As a mineral, calcium easily becomes charged. It turns into Ca2+ – it has two positive charges. This ionic form of calcium is attracted to various negatively charged molecules – including the different forms we’ll discuss in this article: carbonate, citrate, lactate, and gluconate.

Unlike the ionic form, calcium salts are stable and lack electrical charge. Some are found in nature, while others are synthetically created in the lab.

Each calcium salt differs in the amount of pure or elemental calcium it provides. Calcium salts can also vary in how well they are absorbed, how they taste, and how easily they dissolve in water.


Good options

  • Calcium citrate and calcium lysinate are absorbed well.
  • Calcium carbonate has the highest amount of elemental calcium but is poorly absorbed.
  • Calcium hydroxyapatite might be more effective for bone health.

Lacking evidence

  • Calcium AEP lacks evidence
  • Calcium gluconate, calcium lactate, oyster shell, and coral calcium are not more effective despite being more expensive.

Possibly dangerous

  • Calcium orotate is unsafe and should be avoided.

Calcium Salts Overview

1) Calcium Carbonate

Calcium carbonate is the most common calcium compound in the world. It is found in rocks, particularly limestone, as well as in pearls, seashells, and eggshells. In fact, the typical eggshell is about 94% calcium carbonate [3, 4].


Most supplement manufacturers opt in to use calcium carbonate over other salts due to its widespread availability, low price, and extensive medical research. Plus, it contains 40% of elemental calcium, the highest of any calcium salt [5].


On the downside, calcium carbonate is poorly absorbed: only about 20% will pass into the bloodstream from the gut [5].

In addition, calcium carbonate requires an acidic environment to properly dissolve. Thus, people with low stomach acid due to gut problems or those who take medications for acid reflux (histamine-2 blockers and proton-pump inhibitors) will have even more trouble absorbing it [6, 7].

Another disadvantage is its low solubility in water. As a result, calcium carbonate powder can’t be dissolved in water or juice and taken as a drink [6, 7].

2) Calcium Citrate

Calcium citrate is a complex of calcium and citric acid.


Around 40% of calcium citrate is absorbed, which is at least two-fold better than calcium carbonate. People with low stomach acid will absorb it much easier than carbonate [5].

Another advantage of the citrate form is its greater solubility in water. Calcium citrate powder is easy to mix with water and take as a drink, which offers options to people who want to (or need to) avoid large capsules or tablets [6, 7].

Calcium citrate might also be the right choice for people who are prone to kidney stones. Citrate salts can reduce the formation and growth of the most common type of kidney stones (oxalic acid stones) [8].


It only contains 21% of elemental calcium, less than calcium carbonate [5].

3) Hydroxyapatite

Though not technically a salt, hydroxyapatite is a popular form of calcium in supplements. Hydroxyapatite is a mineral complex that naturally contains calcium and phosphate. It is used to store calcium in the teeth and bones, making up to 70% of the weight of the bones. Hydroxyapatite also contains varying amounts of magnesium and trace elements [9, 10].

Nowadays, hydroxyapatite is used in medicine to make biocompatible implants or bone transplants [11, 12].


In a trial on 100 postmenopausal women, hydroxyapatite was as beneficial as carbonate or citrate for preventing bone loss. But interestingly, hydroxyapatite raised blood calcium levels less than both carbonate and citrate. This could mean that hydroxyapatite is more effective at getting into bone cells – where calcium belongs [13].

Combining calcium hydroxyapatite with ossein may be a better solution than hydroxyapatite alone. Ossein is a substance that makes bones flexible and is mostly made up of collagen. According to a review of clinical studies, this combination is more effective than calcium carbonate at preventing bone loss [14].

A trial with 107 people found that chewing gum with calcium hydroxyapatite reduced tooth sensitivity. Many people suffer from sensitivity, often worsened by cold foods and drinks. If you’re one of them, chewing gum with hydroxyapatite might help [15].


Studies on supplemental calcium hydroxyapatite are few.

In sum, calcium hydroxyapatite may be more effective than other forms, but the evidence is still too weak to justify its hefty price tag.

4) Calcium Lysinate

Calcium lysinate is a salt of calcium and the amino acid lysine.


Calcium lysinate might be superior to both carbonate and citrate. In 24 people with bone disease, calcium lysinate was more effective than carbonate and citrate at raising calcium levels. Even more importantly, the lysinate form improved bone density to a greater extent [5].

This salt provides 30% of elemental calcium. According to one trial, its absorption rate reaches an astounding 89%, more than double that of any other form. Additionally, L-lysine enhances calcium absorption from the gut while preventing the loss of calcium in the kidneys [5].


Unfortunately, calcium lysinate supplements are still not widely available.

5) Oyster Shell & Coral Calcium


Might be similar to calcium carbonate.


Coral and oyster shell calcium have become increasingly popular. Manufacturers claim that coral calcium will promote good health, improve your sleep, and even “make your body more alkaline.” Much of the hype is due to a myth about the people who live in the Okinawa region of Japan, where the corals grow. Companies started spreading an appealing story: people living in Okinawa have the longest lifespan and the lowest rates of cancer and other chronic diseases because they regularly drink “coral water.” No evidence supports such claims.

Both coral and oyster shell calcium are simply calcium carbonate with a sophisticated name and a matching price tag. What’s worse, reports indicate these “natural sources” of calcium are likely to be heavily contaminated with lead [16, 17, 18].

6) Calcium Orotate & AEP Calcium


Companies make bold claims about calcium orotate. Some state that it’s the single most effective and most highly absorbed form of calcium.


Most of these claims cite the highly controversial research of the late 20th-century doctor Hans A. Nieper, a German practitioner who claimed to treat cancer and other serious diseases with alternative medicine. Nieper is best known for his research on lithium orotate. His approach goes under various names, from “Nieper therapy” to “metabolic supplementation” [19, 20, 21, 22].

Nieper considered that orotate is the most efficient and far-reaching carrier for minerals like calcium and magnesium in the body.

He also patented AEP calcium (calcium aminoethyl phosphate). Although the body uses phosphorylethanolamine – a compound of AEP calcium – to build cells (and their phospholipids), it’s unclear if AEP calcium has any benefits. Studies with this chemical are nonexistent [23, 24].

Additionally, no studies to date have investigated calcium orotate (or AEP calcium). Its safety and efficacy are unknown. Orotate is known to promote tumors in animals. The European Food Safety Authority (EFSA) considers all orotate salts unsafe. Avoid this form [25].

Other Salts

Other forms of calcium salts are available, such as calcium gluconate and calcium lactate. Both contain little calcium and are not well-researched. They are also more expensive, making them a less practical supplement choice [7].

In a trial on 43 patients with high blood fat levels, calcium lactate (510 mg/day) decreased total cholesterol levels by 4% without altering blood calcium levels or causing any side effects [26].

Calcium Supplement Dosage

Understanding Your Daily Needs

Most adults need at least 1,000 mg of calcium per day. Women over 50 years need a bit more, 1,200 mg a day. Teenagers, pregnant and breastfeeding women should get at least 1,300 mg calcium per day [1].

The amount of supplemental calcium you need depends on your diet. If your dietary intake is low, you can supplement with up to 1,000 mg/day, unless directed differently by a doctor. Divided doses of no more than 500 mg work best [27].

Aim to get 1,000 to 1,400 mg of calcium per day from both food and supplements and discuss the best way to reach this goal with your doctor.

Elemental Calcium Content

The different forms of calcium contain varying amounts of elemental calcium. You need to adapt your dosage for each to achieve the same results. The elemental calcium content is typically written on the label and you can use it as a rough guide.

To get 400 mg of elemental calcium, you will need:

  • 1 g of calcium carbonate
  • ~2 g of calcium citrate
  • ~1.5 g of calcium lysinate

To learn about all the pros and cons of calcium supplements, read this post.


Among numerous calcium supplements, calcium carbonate and calcium citrate are proven to be safe and effective. They are also affordable and widely available. Calcium carbonate is the best choice for the average person. It’s higher in calcium, but it is not absorbed as well. People prone to kidney stones and those with low stomach acid should go with calcium citrate instead. Other forms of calcium are often marketed for their superior potency or benefits, although evidence is lacking to recommend their use.

About the Author

Carlos Tello

Carlos Tello

PhD (Molecular Biology)
Carlos received his PhD and MS from the Universidad de Sevilla.
Carlos spent 9 years in the laboratory investigating mineral transport in plants. He then started working as a freelancer, mainly in science writing, editing, and consulting. Carlos is passionate about learning the mechanisms behind biological processes and communicating science to both academic and non-academic audiences. He strongly believes that scientific literacy is crucial to maintain a healthy lifestyle and avoid falling for scams.


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