Calcium Citrate vs. Calcium Carbonate: Which to Take?

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There are many types of calcium supplements, including calcium carbonate, calcium citrate, calcium gluconate, and others. Knowing the differences between the two most common types—calcium citrate and calcium carbonate—can help you decide which one to take.

There are many health benefits of calcium beyond helping you build strong bones. You also need calcium to move your muscles, to send nerve signals between your brain and body, and to help your blood vessels move blood throughout your body.

This article explains how calcium citrate and calcium carbonate work, how they're different, how to take them, and ways to choose the right one for you.

Benefits of calcium supplements
Verywell / JR Bee

How Calcium Citrate and Calcium Carbonate Work

If you're not meeting your daily calcium requirements through diet, you may benefit from taking a calcium supplement. Generally, calcium supplements work best when they are taken with food. Although you can take calcium citrate without food, the stomach acids produced when you eat will help your body absorb more calcium.

The most important thing to look for when choosing a calcium supplement is the amount of elemental calcium the supplement contains. Depending on the manufacturer, the amount of elemental calcium may be listed directly on the label, or the weight may be listed on the calcium tablet itself.

Another way to check for the amount of elemental calcium the supplement contains is by looking at the recommended daily allowance (RDA). The RDA for most individuals is 1000 milligrams (mg) of calcium per day (this varies by age, gender, and special situations, including pregnancy). If the bottle states a tablet contains 40% of the RDA of calcium, then it contains 400 mg of elemental calcium.

Differences: Calcium Carbonate vs. Calcium Citrate

Calcium supplements are generally made with one of two sources of elemental calcium: calcium carbonate or calcium citrate. There are several differences to note:

Calcium Carbonate
  • Contains the highest concentration of elemental calcium at 40% by weight

  • Tablets are often smaller and fewer are needed to meet the RDA

  • Shouldn't be taken on an empty stomach or if you have low stomach acid

  • Can cause bloating or constipation

  • Tends to be the least expensive

  • Possible side effects include: nausea/vomiting, belching, dry mouth, increased urination, metallic taste, fatigue, bone pain

Calcium Citrate
  • Contains the second highest concentration of elemental calcium at 21% by weight

  • Tablets are often bigger and more are needed to meet the RDA

  • Absorbs well when taken without food and is good for people on antacids

  • Doesn't constipate and is better for people with digestive issues

  • Can be more expensive

  • Possible side effects include: nausea/vomiting, belching, low blood pressure, headache, increased urination, loss of appetite, fatigue

Most people do not experience side effects when taking the RDA for calcium supplements. Contact your healthcare provider if side effects are severe or do not go away, as this could mean you have too much calcium in your system.

Although rare, allergic reactions can occur. Seek medical attention if you develop symptoms of an allergic reaction, such as a rash or hives; wheezing; difficulty breathing, swallowing, or talking; tightness in your chest; or swelling of the face, mouth, throat, or lips.

How to Take Calcium Supplements

There are limits on how much calcium your body can absorb at once, and other foods and medications can impact calcium absorption. Here are some tips on taking your calcium to maximize its benefits:

  • Meals: Different types of calcium vary in whether they're absorbed best with or without food. Calcium carbonate should be taken with meals. Calcium citrate should be taken on an empty stomach.
  • Medications: Calcium should not be taken with certain medications, including antibiotics, iron supplements, high blood pressure medications, and others. Calcium can bind to these medications and diminish their absorption. Check with your pharmacist about medication interactions.
  • Vitamin D: Calcium is best absorbed when taken with vitamin D. Many supplements are produced with both calcium and vitamin D included.

Dosages of Calcium Citrate and Calcium Carbonate

Follow your healthcare provider's advice on what's best for you. Generally, calcium should be taken in divided doses, rather than all at once. Separate doses into twice or three times daily for optimal absorption.

Don't take more than 500 mg at once. This allows more calcium to be absorbed by the body and will reduce side effects like gas, bloating, and constipation.

How to Choose the Supplement for You

There are positives and negatives to both calcium carbonate and calcium citrate. Read the recommendations for when a supplement you are considering should be taken, and consider whether that fits into a reasonable schedule for you. Look at the amount of elemental calcium contained in the supplement to ensure you would consume an adequate dose.

Supplements aren't regulated by the Federal Drug and Food Administration, which means they don't go through the strict testing and verification processes pharmaceutical products must pass. Some supplements contain potentially dangerous levels of lead. Those made from unrefined oyster shell, bone meal, or dolomite tend to have especially high levels of lead.

Look for calcium that has the United States Pharmacopeia (USP) verification symbol, a sign that levels are acceptable. Products with "purified" on the label are equally recommended.

People with or at risk of certain medical conditions may need additional calcium:

  • Osteoporosis: Calcium supplements can help prevent osteoporosis. Osteoporosis increases your risk of bone fractures. Older people and postmenopausal people may benefit from taking calcium supplements. The best form of calcium for osteoporosis will depend on your specific situation. If you have side effects, you may need to try different types and different brands until you find the best fit.
  • Kidney stones: Taking calcium may help reduce the risk of kidney stones. Calcium citrate is recommended for people at risk for kidney stones. This supplement helps you excrete more urinary citrate, which protects against the formation of stones. It may even help you prevent getting kidney stones again after you've already had them.
  • PMS symptoms: Calcium may be able to reduce some PMS symptoms. It has some effect on fatigue, swelling, and pain, and an even greater effect on depression.

Summary

If you're not getting enough calcium from your diet, calcium supplements can help you get your recommended daily allowance. Calcium citrate and calcium carbonate are different types of calcium supplements that can help you meet your calcium goals.

It's generally recommended to take calcium supplements with food. Calcium carbonate shouldn't be taken on an empty stomach. However, calcium citrate absorbs well without food. Calcium citrate and calcium carbonate differ in calcium content, price, and side effects, too.

Talk to a healthcare provider about your calcium needs. You may benefit from taking calcium if you are at risk of osteoporosis or kidney stones. Supplements can contain toxic substances, so look for the USP symbol or "purified" on the label.

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Institutes of Health Office of Dietary Supplements. Calcium fact sheet for health professionals.

  2. Institute of Medicine (US) Committee to Review Dietary Reference Intakes for Vitamin D and Calcium. Dietary Reference Intakes for Calcium and Vitamin D. National Academies Press.

  3. Wiria M, Tran HM, Nguyen PHB, Valencia O, Dutta S, Pouteau E. Relative bioavailability and pharmacokinetic comparison of calcium glucoheptonate with calcium carbonatePharmacol Res Perspect. 2020 Apr;8(2):2. doi:10.1002/prp2.589

  4. Watson J, Lee M, Garcia-Casal MN. Consequences of inadequate intakes of vitamin A, vitamin B12, vitamin D, calcium, iron, and folate in older personsCurr Geri Rep. 2018 Apr;7(2):103-113. doi:10.1007/s13670-018-0241-5

  5. U.S. Preventive Services Task Force. Vitamin D, calcium, or combined supplementation for the primary prevention of fractures in community-dwelling adults: Preventive medication.

  6. National Institutes of Health Office of Dietary Supplements. Calcium consumer fact sheet.

  7. MedlinePlus. Calcium supplements.

  8. Palermo A, Naciu AM, Tabacco G, et al. Calcium citrate: from biochemistry and physiology to clinical applications. Rev Endocr Metab Disord. 2019;20(3):353-364. doi:10.1007/s11154-019-09520-0

  9. Shobeiri F, Araste FE, Ebrahimi R, Jenabi E, Nazari M. Effect of calcium on premenstrual syndrome: a double-blind randomized clinical trial. Obstet Gynecol Sci. 2017;60(1):100-105. doi:10.5468/ogs.2017.60.1.100

By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.