What's The Difference Between Calcium Citrate vs Calcium Carbonate?

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    Calcium citrate is better absorbed than calcium carbonate and can be taken with or without food. Magnesium & vitamin D are required for healthy calcium levels.

    Why Do You Need Calcium?

    Calcium is a mineral perhaps most commonly known for its importance in the health of teeth and bones, but it does so many other things, too. You need calcium for a well-functioning nervous system, heart health, muscle growth and contraction, maintaining a healhy pH balance, as well as thyroid health.

    Calcium is considered one of the “macro minerals” along with magnesium, sodium, and potassium, all of which your body needs in relatively large amounts compared to trace minerals. You can get it through eating foods rich in calcium which include dairy products, cooked dark leafy greens, small bone-in fish like sardines, and white beans.

    You can also get calcium in supplement form, the most common types being calcium citrate and calcium carbonate. Let’s review these two types of calcium supplements.

    What is Calcium Citrate?

    Calcium citrate is an over-the-counter dietary supplement that contains calcium and citric acid. It is a form of calcium that is easily absorbed by the body and is commonly used to boost calcium levels.

    Calcium citrate is different from other forms of calcium, such as calcium carbonate, in that it does not require stomach acid to be absorbed. This makes it a good option for people who have low stomach acid or are taking medications that decrease stomach acid production. This also means that it can be taken without food or outside of a mealtime when stomach acid may be lower.

    What is Calcium Carbonate?

    Calcium carbonate is another common form of calcium supplementation. When calcium carbonate is consumed, it is broken down by stomach acid to release calcium for absorption. The carbonate portion actually neutralizes some of the stomach acid in the process, so it is important to have adequate levels of stomach acid if taking calcium carbonate. This also means that calcium carbonate should be taken with a meal when stomach acid is present to a higher degree.

    What's the Difference?

    As discussed, calcium citrate does not require stomach acid for absorption, while calcium carbonate does. Calcium citrate may be a better option for those who have lower stomach acid or are taking medications that reduce stomach acid levels. Stomach acid levels can decline with age and even with stress, so these factors should be taken into account when choosing a calcium supplement.

    Calcium carbonate is usually a more affordable form of calcium than calcium citrate.

    Can you Take them Together?

    While it is possible to take calcium carbonate and calcium citrate supplements together, it is important to note that the two forms of calcium have different absorption rates and requirements, so it is best to take them at different times of the day to maximize their absorption and effectiveness.

    You also want to make sure that the total amount of calcium you are taking is appropriate for you. You can talk to a registered dietitian or your doctor to determine the appropriate types, dosages, and timing for your individual needs.

    Is One Better To Treat Low Calcium Levels?

    Calcium citrate is better absorbed than calcium carbonate by about 22-27% regardless of whether taken with or without food. Choosing calcium citrate over calcium carbonate may be a better option for someone who wants to get a higher dose of absorbable calcium per serving.

    In a study of postmenopausal women, those who took calcium citrate showed more significant decreases in bone resorption compared to women who took calcium carbonate. Bone resorption is the process of bone minerals being absorbed from the bone into the body and therefore decreasing bone density. Postmenopause is a time in which bone mineral density often reduces due to reductions in estrogen levels, so calcium as well as other nutrients required for bone health are of great importance during this time.

    Care/of’s Calcium Plus formula contains algae-derived calcium in combination with magnesium and vitamins D and K2 to boost calcium absorption and healthy use in the muscles and bones, where the majority of calcium is stored. This calcium is sustainably sourced from red algae which is well absorbed and rich in trace minerals.

    What Helps Calcium Absorption?

    There are several factors that can help enhance the absorption of calcium by the body:

    Vitamin D: Vitamin D plays a crucial role in calcium absorption. It helps the body absorb calcium from food in the intestine and also regulates the levels of calcium in the blood. Sunlight exposure is the most common way to get vitamin D, but it can also be obtained from foods such as egg yolks, fatty fish, and fortified milk. More vitamin D is not always better. We need the right amount in our body to support proper calcium use.

    Magnesium: Magnesium is also important for calcium absorption and bone health. It helps convert vitamin D into its active form, which enhances calcium absorption. Good sources of magnesium include shelled pumpkin seeds (pepitas), cooked leafy greens, almonds, cashews, cocoa, and soybeans.

    Acidic environment: An acidic environment in the stomach is necessary for calcium absorption. Foods and beverages that are high in acid, such as citrus fruits and juices, may help facilitate calcium absorption. Supporting stress management especially at mealtimes can support adequate stomach acid levels.

    Exercise: Weight-bearing exercise, such as walking, running, and strength training, helps improve bone health by enhancing the deposit of calcium in the bone. Exercise can also enhance intestinal calcium absorption. Overall, exercise is a win-win for healthy calcium use in the body.

    Avoiding high levels of certain substances: High levels of caffeine, alcohol, and sodium can interfere with calcium absorption.

    Calcium load per serving: The gut can only absorb so much calcium at a time. Studies show that calcium absorption is highest at doses of 500 mg or less, and otherwise is less efficiently absorbed at higher single doses. For this reason, it is best to spread your calcium intake throughout the day.


    The Recommended Dietary Allowance (RDA) for calcium is 1,000-1,200 mg per day for most adults, and has an upper limit of 2,000-2,500 mg daily from food and supplements. Be sure not to exceed this amount unless specifically instructed by your doctor. Mineral consumption impacts the utilization of other minerals in the body in a delicate balance, so it is best to aim for adequacy rather than exceed it.

    Potential Side Effects

    Some people may experience gastrointestinal side effects including gas, bloating, and/or constipation when taking calcium carbonate, since it can affect stomach acid levels and spur indigestion. These effects are generally less common with calcium citrate. Taking calcium citrate or taking calcium in smaller doses during the day may reduce side effects.

    Who Should Take A Calcium Supplement?

    Individuals who may benefit from taking a calcium supplement include:

    • Those who have difficulty consuming enough calcium from their diet, which may include those who are lactose intolerant, vegan, or have dietary restrictions that limit calcium intake.
    • Postmenopausal women, who often need bone health support following the decline in estrogen levels after menopause.
    • Those taking certain medications that can interfere with calcium absorption. In such cases, a calcium supplement may be recommended by a healthcare provider to help meet daily calcium needs.
    • Older adults, since calcium absorption tends to decrease with age and may be in part due to a common decline in stomach acid levels in older adults.
    • Those who are pregnant or breastfeeding.
    • Those who smoke cigarettes or drink alcohol regularly, since both activities can deplete calcium in the body.

    It may be helpful to get your RBC Magnesium (RBC = red blood cell) and vitamin D levels checked first before supplementing with calcium since adequate levels of these nutrients are required for appropriate absorption and use of calcium in the body.

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    Dr. Carla Montrond Correia ND, CNS
    Medical Content Manager
    Dr. Montrond-Correia is a licensed naturopathic physician and a certified nutrition specialist (CNS). She holds degrees from University of Bridgeport, Georgetown University, and University of Saint Joseph, and supplemented her education with internships in the health and wellness space. She's focused on research, herbal medicine, nutrigenomics, and integrative and functional medicine. She makes time for exercise, artistic activities, and enjoying delicious food.
    Victoria Peck-Gray, RD
    Freelance Contributor
    Victoria is a registered dietitian and functional nutritionist who helps people with resistant weight loss and PCOS transform their metabolic health and lose weight through a functional nutrition and lifestyle approach that addresses root causes. She is owner of her private practice, Wonderfully Made Nutrition and also leads her group metabolic coaching program for women called The 4 Method.