Evidence: High Possible Benefits: Reasonable Safety: Low
TABLE OF CONTENTS
What is calcium carbonate?
Calcium carbonate is a popular supplemental form of calcium. Calcium supplements are most helpful if you are deficient in this nutrient. If you already get enough from food, you should not take calcium carbonate as higher doses can lead to various side effects. This article is about the main benefits of calcium carbonate, its potential side effects, the best time to take it, and more.
What does calcium carbonate do?
Along with phosphorus, calcium is the main mineral in our bones and teeth. These two minerals form tight bonds in the bones and teeth to keep them strong.
99% of the calcium in our bodies is stored in the bones. The bones of an average person contain about 1-2 kg of this mineral.
Unfortunately, if carriers of these minerals (most notably vitamin D and vitamin K) are insufficient, calcium and phosphorus may create bonds outside the bones and teeth. For example, this can happen in the kidneys, leading to kidney stones. In worse cases, calcium and phosphorus may calcify blood vessels, possibly leading to heart disease.
Calcium also plays a vital role in the release of all neurotransmitters, clotting the blood after an injury, contracting our muscles, and more.
Possible benefits
It is important to note that all of the potential benefits mentioned below are dose-dependent. Generally, the higher the dose, the more pronounced the effects are. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.
Many possible benefits fall under the umbrella of ‘correcting a deficiency’ and are therefore not mentioned in the article. If you are deficient, calcium carbonate can certainly affect your cognition, performance, and overall health in a positive way.
Major benefits
Correcting or preventing a deficiency – Calcium deficiency can be terrible for health and overall quality of life. Fortunately, a severe deficit is relatively rare. A mild deficiency is more common and can lead to many problems mentioned later in the article. If you are experiencing symptoms of deficiency or know that your calcium levels are too low, helping you get back to the optimum is the main benefit of calcium carbonate.
Minor benefits
Reduced symptoms of PMS – High doses (500-1000 mg/d) have been shown to reduce pain related to PMS.
Possible side effects
These side effects are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.
Kidney stones – Calcium carbonate can accumulate in your kidneys and form calcium oxalate kidney stones. This is especially the case in people who are deficient in vitamin D and vitamin K.
Soft tissue calcification – Calcium carbonate might enter your system too quickly and promote soft tissue calcification. This is especially the case if you take the supplement on empty stomach and/or are deficient in vitamin D and K.
Calcium-alkali syndrome – This syndrome usually occurs in pregnant, bulimic, or older women who take this mineral. It often makes people unusually thirsty and pee too much. It can also lead to confusion, weakness, depression, and irregular heartbeat. Antacids and NSAIDs can significantly increase this risk. This effect is also most common with calcium carbonate, oxide, and hydroxide. Other forms may be safe in this regard.
Diarrhea – Diarrhea caused by this supplement is not dangerous (assuming it doesn’t lead to severe dehydration) and usually only occurs if you take very high doses at once.
Nausea – Just like diarrhea, this side effect is not dangerous but can be unpleasant.
Hypercalcemia – While severe toxicity is rare, taking high amounts of calcium carbonate could lead to hypercalcemia over time. Those suffering from hypercalcemia usually have hard and brittle bones. Toxicity can also cause stomach upset, nausea, vomiting, and constipation. This is why it’s best to avoid very high doses. Specifically, you want to stay below 500 mg a day unless you have a great reason to take more.
Cardiotoxicity – Combining calcium carbonate and digitoxin or digoxin is shown to be cardiotoxic.
Contamination – Contaminated supplements are uncommon in the USA and other well-regulated countries. However, if you wish to buy products from China, India, or other countries without strict regulations, beware that the supplements may be contaminated. Either way, you need to choose the brand you order from wisely. It is highly recommended to check the certificates or read through some reviews for the specific product before you buy it. The FDA (Food and Drug Administration) has the power to regulate dietary supplements but can only do so after they have been on the market for a while. That’s because supplement companies are not obligated to announce to the FDA when releasing a new product on the market. The FDA has to discover the product and test it for potential impurities, which can take a lot of time. During that time, the supplement can be sold on the market even if it’s impure. Also, supplement companies can change their manufacturers without announcing it to the FDA.
Who should not take calcium carbonate?
You should probably avoid taking the supplement if you:
are willing to take a safer type of calcium, such as calcium citrate
already consume enough calcium from food
experience a severe adverse reaction after taking the supplement
went through a menopause
are deficient in vitamin D (while calcium decreases your need for vitamin D to some extent, taking this mineral without enough vitamin D can lead to soft tissue calcification, kidney stones, and other side effects)
are deficient in vitamin K (this vitamin, just like vitamin D, is needed to transport calcium and prevent it from going into the wrong places, such as soft tissues and kidneys)
are on a tight supplement budget (since there are more cost-effective supplements on the market for most people)
Who will benefit the most?
You should consider taking the supplement if you:
experience symptoms of deficiency, or you know you are deficient based on blood tests
don’t get enough from food (the easiest way to find out how much of this nutrient you are getting in your diet is to track your food intake for a while with Cronometer.com)
consume too much phosphorus (phosphorus increases your calcium needs)
Symptoms of calcium deficiency
The most common signs of deficiency include:
fatigue
dizziness
brain fog
weak bones
osteoporosis
osteopenia
rickets
osteomalacia
tetany
Keep in mind that these signs are just indications of a deficiency. If you experience some or even most of them, it does not necessarily mean you need more calcium. On the other hand, some people may be deficient even though they are completely asymptomatic.
With that said, if you experience many or most of these symptoms, there is a high chance that you are not getting enough calcium. The more of these symptoms you have and the more severe they are, the more likely you are to have a deficiency.
Types of calcium supplements
The different types of calcium supplements include:
Calcium carbonate – This is the most popular form found in most multivitamins and multimineral supplements. Unfortunately, it also seems to be the worst one to take, along with oxide and hydroxide. These forms are accountable for most reports of the calcium-alkali syndrome.
Calcium oxide – Just like calcium carbonate, this type is very cheap but also inadvisable, especially for older and pregnant women or those who take antacids and NSAIDs.
Calcium hydroxide – Everything said about calcium oxide also applies to this form.
Calcium citrate – This is the best form to take. It has the best safety record and is proven to be effective for correcting a deficiency. Citrate is also great for preventing kidney stones.
Calcium malate – While not as studied as calcium citrate, this form appears to be safe and highly absorbable. It doesn’t seem to have additional benefits and is usually more expensive than the citrate form, which is why citrate is a better choice for most people.
Calcium lactate – The same said about calcium malate also applies to calcium lactate, gluconate, glubionate, and sulfate.
Calcium gluconate
Calcium glubionate
Calcium sulfate
Calcium phosphate – This is the form found in most foods. In supplements, it further divides into tricalcium phosphate, dicalcium phosphate dihydrate, and other types. Calcium phosphate may be superior to calcium citrate but there aren’t many studies to support this.
Calcium glycerophosphate – Some people claim that calcium glycerophosphate is less likely to cause gastrointestinal problems. However, this claim is not supported by quality science. Calcium glycerophosphate is likely as good as phosphate but phosphate or citrate are safer choices backed by more data.
Bone meal – While this is a natural form providing bioavailable calcium, bone meal tends to be contaminated with high amounts of lead. Also, those with low stomach acid have a problem absorbing calcium or other nutrients from bone meal. This food/supplement contains relatively high amounts of collagen which can be both a good thing and a bad thing. While collagen can be beneficial for some aspects of health, it can also be harmful in those with calcium oxalate kidney stones. In general, this should not be a big concern with collagen but since bone meal contains high amounts of calcium, it increases the risk for kidney stones. Therefore, if kidney stones are a concern for you, other supplemental types are a better way to go.
Eggshells – Eggshells contain mostly calcium carbonate and thus are not recommended to people at risk of the calcium-alkali syndrome. Eggshells also contain low amounts of other minerals but also possible contaminants.
Oyster shells – Everything said about eggshells applies to oyster shells as well.
Coral calcium – The composition of this form is somewhere between eggshells and pure calcium carbonate.
Dolomite – This supplement also contains calcium carbonate and some magnesium.
Of all the forms above, calcium citrate appears to be the safest and the most reliable. Calcium phosphate, malate, gluconate, and sulfate are also great choices. Avoid calcium carbonate, oxide, and hydroxide to prevent the calcium-alkali syndrome.
How much calcium carbonate should you take?
The RDA (recommended daily allowance) for this nutrient is 1000 mg for adult men and women. This should be enough for most people to avoid symptoms of deficiency. The RDA for women over the age of 50 and men over 70 increases to 1200 mg/d.
How much calcium we need is greatly dependent on genetics. In some parts of the world, people have been eating less than 300 mg/d and they don’t seem to have more problems related to bone health than populations eating more calcium.
For most people, 1000 mg appears to be the best daily target. However, as little as 300-500 mg should be enough to prevent any signs of deficiency. This amount should provide most of the benefits without meaningful side effects.
Beware that some things increase your need for calcium. These include high phosphorus intake, growing up, and older age.
The tolerable upper limit is 2000-3000 mg, depending on the age group. Higher amounts may cause problems if you take the supplement for a prolonged period. Taking more than 500 mg daily should not be necessary and is not recommended unless you have a great reason to do so.
Food sources of calcium
The absorption of calcium differs from food to food. We absorb about: 50% from cruciferous vegetables (such as broccoli, kale, and cabbage) 30% from milk 25% from legumes 10% from leafy greens
Taking absorption into account, the richest food sources include dairy, soybeans, and some cruciferous vegetables. Specifically, Chinese mustard greens, napa cabbage, and bok choy contain the most calcium out of all popular vegetables and plant foods in general.
The second tier would contain spinach and a few other leafy greens, nuts, seeds, canned fish with bones, figs, grains, and legumes.
The easiest way to find out how much calcium you are getting in your diet is with Cronometer.com. This free app allows you to track all vitamins, minerals, and more.
Best time to take calcium carbonate
This form of calcium is water-soluble, which means you technically don’t have to take it with food to absorb it well.
However, taking this mineral with food is safer as it will not absorb as fast, lowering the risk of soft tissue calcification.
Whether you take the supplement in the morning or the evening doesn’t matter. It does not interrupt your sleep in any way.
Never take a high dose of this mineral at once. Always spread the dose across multiple meals throughout the day.
If you practice time-restricted eating, take one dose with food and the other/s at a different time of the day.
Interactions with other supplements
Vitamin D Vitamin D increases the absorption of calcium carbonate. It also prevents many of the side effects related to calcium carbonate supplementation, namely soft tissue calcification.
Vitamin K This vitamin, just like vitamin D, is needed to transport calcium and prevent it from going into the wrong places, such as soft tissues and kidneys
Sugar alcohols Sugar alcohols, such as xylitol, erythritol, and maltitol increase the absorption of calcium carbonate.
Antacids This combination can lead to the calcium-alkali syndrome. This syndrome usually occurs in pregnant, bulimic, or older women who take this mineral. Antacids can significantly increase this risk.
NSAIDs NSAIDs can have a similar effect to that of antacids when combined with calcium supplements.
Bisphosphonates These include risedronate (Actonel), alendronate (Fosamax), ibandronate (Boniva), zoledronic acid (Reclast), and pamidronate (Aredia). Taking calcium carbonate with bisphosphonate drugs for osteoporosis reduces the absorption of bisphosphonates.
Aspirin The mineral reduces the efficacy of aspirin.
Lithium Long-term usage of lithium leads to hypercalcemia in 10%-60% of users. Combining lithium with calcium carbonate would worsen this possible side effect.
Where to buy calcium
Amazon seems to be the best option for ordering calcium supplements in most countries. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the internet.
Beware some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.
FAQ
You can take the supplement daily and do not need to cycle it. However, it is certainly not a problem if you don’t take it daily. Not taking the supplement every once in a while could lead to better absorption.
All of these options are fine. The two most important things to consider are the price and dosing. Powders are almost always the cheapest form. However, you may need a highly accurate scale to dose them correctly (preferably 0.001g). You can get one for as little as $20 from Amazon. Dosing the powders also takes some time that can add up over months or years. The disadvantage of capsules is that they often contain bovine gelatine, which rarely comes from an ethical source.
Yes. The nutrient doesn’t impact your sleep in any negative way in the short term. Just make sure to take the supplement with food to lower the possible side effects.
The supplements should not become harmful once they exceed the expiration date, but they can lose potency over time.
Keep the supplements in a cold, dark, and dry place, and they should remain just as potent for many months or even years.
The supplement doesn’t directly reduce acne, unfortunately.
While severe toxicity is rare, too much calcium carbonate in the system can cause multiple health problems, such as kidney stones and soft tissue calcification, increasing the risk of a heart attack. It is best to stay below 500 mg daily to prevent these side effects.
Of all the supplemental forms, calcium citrate appears to be the safest and the most reliable. Calcium phosphate, malate, gluconate, and sulfate are also great choices. Avoid calcium carbonate, oxide, and hydroxide to lower the risk of calcium-alkali syndrome.
The most common reason people become deficient is that they don’t get enough of this nutrient from their diet. However, many things can hurt your calcium status and increase your need for this nutrient. These include high phosphorus intake, growing up, and old age.
You may need more of the nutrient if you: – experience signs of deficiency, or know that you are deficient from blood tests – don’t get enough from food (the easiest way to find out how much of this nutrient you are getting in your diet is to track your food intake for a while with Cronometer.com) – consume too much phosphorus (phosphorus increases your calcium needs)
Calcium from the supplement stays in your bones for a very long time.
In the long term, it typically takes about 6-12 months of taking the supplement to begin noticing the benefits related to correcting a deficiency.
Most calcium carbonate supplements are vegan-friendly but always check the label to be sure. If you buy the mineral in a capsulated form, beware that the capsules often contain animal-based gelatine. Instead, find a brand that puts its products into cellulose capsules.
This form of calcium is water-soluble, which means you don’t have to take it with food to absorb it well. However, it is still much better to take the supplement with food or right after to lower possible side effects, including soft tissue calcification.
No, it doesn’t. The supplement does not interfere with fasting in any significant way. However, taking it with a meal is still better if you wish to minimize possible side effects.
References
Most of the information provided in this guide is supported by scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything said in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.
