Anastasia, RDN, CD-N, is a writer and award-winning healthy lifestyle coach who specializes in transforming complex medical concepts into accessible health content.

Lana Butner, ND, LAc, is a board-certified naturopathic doctor and licensed acupuncturist in New York City.

Calcium is a mineral essential for healthy teeth and bones. It also helps keep blood vessels, muscles, and nerves healthy, and supports hormone function. Calcium is available in many foods, including dairy products, salmon, and green, leafy vegetables.

Calcium supplements are typically sold in the form of calcium carbonate or calcium citrate. Calcium citrate is a calcium salt that's easier to absorb. While you can take calcium citrate without a meal, it absorbs best when taken with food. Calcium citrate is often the better choice if you take heartburn medication or have digestive issues, since stomach acid isn't required for absorption.

This article explains calcium citrate's uses, potential side effects, and dosage.

Dietary supplements are not regulated in the United States, meaning the Food and Drug Administration (FDA) does not approve them for safety and effectiveness before products are marketed. When possible, choose a supplement that has been tested by a trusted third party, such as USP, ConsumerLabs, or NSF.

However, even if supplements are third-party tested, that doesn’t mean that they are necessarily safe for everyone or effective in general. It is important to talk to your healthcare provider about any supplements you plan to take and to check in about any potential interactions with other supplements or medications.

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or doctor. No supplement is intended to treat, cure, or prevent a disease.

Calcium is an essential mineral that supports multiple systems throughout the body. You must maintain adequate calcium levels for your heart, nervous system, and muscles to function properly.

Calcium is probably best-known for making strong bones. But beyond bones, calcium supplementation's possible benefits include potentially reducing the risk of cancer, heart disease, preeclampsia, and metabolic syndrome. It may also help some people maintain a healthy weight. Research supports some of these uses more than others.

Due to calcium's known role in establishing healthy, strong bones, some research has focused on whether calcium supplementation could prevent age-related bone mineral density (BMD) loss and fractures. Unfortunately, the research has had mixed results.

For example, a 2021 study evaluated the association between dietary calcium intake and BMD in older adults using data from the National Health and Nutrition Examination Survey (NHANES, 2001-2006). In 2,904 participants, researchers found that higher dietary calcium intake was associated with greater lumbar (vertebrae of the lower spine) BMD. Researchers found this benefit only in women but not in men.

On the other hand, a 2019 study on calcium intake and bone loss in postmenopausal people with osteopenia (low bone density) found no impact on bone loss. In an analysis of observational data obtained from a randomized controlled trial, researchers compared bone mineral density (BMD) and bone mineral content (BMC) in participants who took calcium supplements and those who took a placebo. Researchers found no relationship between bone loss and calcium intake.

The FDA has approved health claims that say adequate intake of vitamin D and calcium may reduce the risk of osteoporosis.

Due to calcium's protective effect on cells, some research has explored its potential to reduce cancer risk. However, overall, the research is mixed.

For example, a 2017 study evaluated calcium and vitamin D supplementation's effect on cancer incidence in older women. The four-year, double-blind, placebo-controlled, population-based randomized clinical trial split 2,303 postmenopausal participants into a treatment (2,000 IU/day of vitamin D3 and 1,500 mg/day of calcium) or placebo group. The treatment group did not have significantly lower cancer risk at four years compared with the placebo.

However, another older 2007 study suggested calcium plus vitamin D does have benefits. The randomized controlled trial compared the effect of calcium supplementation alone to calcium and vitamin D supplementation on cancer risk. Researchers randomized 1,179 postmenopausal participants into groups receiving 1,400-1,500 mg calcium/day alone, calcium plus 1,100 IU vitamin D3/day, or placebo. Cancer incidence was lowest in the calcium+D group.

Calcium's ability to reduce lipid absorption has led to some research on its ability to reduce cardiovascular disease risk. However, the results have been mixed, with some research indicating no effects.

For example, a 2015 study evaluated 1999–2010 NHANES data on calcium intake and hypertension (high blood pressure) in adults with obesity. Among 14,408 adults, researchers found that calcium intakes were 10% lower in those with hypertension and obesity.

However, some studies have found that calcium supplementation increases the risk of heart disease. For example, a 2021 meta-analysis of clinical trials investigated the association between calcium supplements and cardiovascular disease risk. In the 13 double-blind, placebo-controlled RCTs, calcium supplements significantly increased the risk of heart disease by 15% in healthy postmenopausal people.

The National Osteoporosis Foundation and American Society for Preventive Cardiology determined that calcium (with or without vitamin D) has no beneficial or harmful relationship to the risk of developing cardiovascular disease.

In addition to the potential health benefits listed above, some people use calcium for:

Some people may develop a calcium deficiency when their intakes are lower over time than recommended levels, they have a specific risk factor for lower than normal levels, or there is a particular reason they are unable to digest or absorb calcium.

When you don't get enough calcium from outside sources, such as food or supplements, or you don't absorb calcium well, your body uses calcium in your bones to keep blood levels up. Over time, pulling calcium from your bones weakens them and increases the fracture risk.

People most at risk of calcium deficiency are postmenopausal people and those who do not eat dairy.

A calcium deficiency may need to be properly identified and diagnosed by a healthcare provider through specific lab tests. However, certain symptoms and health conditions may signify a deficiency. These include:

For women over age 50, a bone density screening is an excellent way to assess bone status. If you're unsure whether you're meeting your calcium needs, a dietitian may be able to help.

Your healthcare provider may recommend you take calcium citrate for bone health. However, consuming a supplement like calcium citrate may have potential side effects. These side effects may be common or severe. 

Common side effects from calcium include:

Most of the time, you can reduce the symptoms by taking smaller doses throughout the day or taking your supplement with a meal.

Rarely, calcium supplementation is associated with more severe conditions, including:

Controversy exists over the benefits of calcium supplements. Some researchers suspect calcium supplements aren't effective at reducing bone fractures and may cause other issues.

If you have a history of kidney disease, kidney stones, cancer, high calcium blood levels, or parathyroid gland disorder, talk to your healthcare provider before taking calcium citrate supplements.

In addition, calcium supplements may interact with certain medications, including:

Be sure to discuss calcium citrate supplementation with a healthcare provider and ask a pharmacist if you're unsure about possible interactions.

Always speak with a healthcare provider before taking a supplement to ensure that the ingredients and dosage are appropriate for your individual needs. 

When it comes to calcium supplements, recognizing the exact dosage can be confusing. That's because pure calcium (elemental calcium) is mixed with a filler when manufacturing supplement pills.

For instance, calcium carbonate is 60% carbonate and 40% elemental calcium. Calcium citrate is technically just 21% calcium. Read the label to identify how much pure calcium is provided per pill.

The recommended dietary allowance (RDA) for calcium is as follows:

As with any dietary supplement, taking more calcium than needed may do more harm than good. So, only take a supplement if you know you aren't getting enough from food and beverages and after consulting with a healthcare provider.

To avoid toxicity, be aware of the appropriate recommended dosages (above) and keep the upper limit in mind. For calcium, the safe upper limit established by the Food and Nutrition Board is as follows:

If you consume more than this amount or more than what is recommended by a healthcare provider, you may want to seek medical attention.

Store calcium in a cool, dry place. Keep it away from direct sunlight. Discard after one year or as indicated on the packaging.

Calcium citrate is a form of calcium supplement. Some people take calcium citrate for bone health and to prevent cancer and heart disease. However, research is mixed on most of these uses.

Calcium carbonate and calcium citrate are the two most common calcium supplements. Calcium citrate absorbs better when taken with a meal. In addition, calcium carbonate is 40% calcium by weight, whereas citrate is 21%.

Calcium is vital for people of all ages. Children and teens are still forming their bones and should be mindful of getting sufficient calcium. Sitting down with a healthcare provider to review your dietary habits can help determine whether your intake is adequate.

Calcium is readily available in foods. Food sources are optimal because they absorb best in the body. However, supplements can also help meet daily requirements when you cannot meet your needs through food sources alone.

Most people can obtain adequate calcium through food. Foods that are high in calcium include:

Calcium citrate is available over the counter. Supplements usually contain 200-300 mg or 500-600 mg when combined with vitamin D. Calcium citrate can be taken on a full or empty stomach at any time of the day.

Calcium absorption is highest in lower doses of calcium. For example, you absorb around 36% of a 300 mg dose, whereas, in a 1,000 mg dose, you absorb only 28%.

Calcium is essential for strong bones, teeth, and muscles. Calcium citrate supplements can help you reach the recommended daily value, especially if you have difficulty absorbing calcium. For most people, it's possible to get enough calcium through food alone. Some people take calcium citrate for bone health and reduce the risk of cancer and heart disease. However, the research on those benefits is mixed.

NIH National Cancer Institute. Calcium citrate.

Yao X, Hu J, Kong X, Zhu Z. Association between dietary calcium intake and bone mineral density in older adults. Ecol Food Nutr. 2021;60(1):89-100. doi:10.1080/03670244.2020.1801432

Bristow SM, Horne AM, Gamble GD, Mihov B, Stewart A, Reid IR. Dietary calcium intake and bone loss over 6 years in osteopenic postmenopausal women [published correction appears in J Clin Endocrinol Metab. 2020 Jan 1;105(1):]. J Clin Endocrinol Metab. 2019;104(8):3576-3584. doi:10.1210/jc.2019-00111

U.S. Food and Drug Administration. Small Entity Compliance Guide: Health Claims on Calcium and Osteoporosis; and Calcium, Vitamin D, and Osteoporosis.

Lappe J, Watson P, Travers-Gustafson D, et al. Effect of vitamin D and calcium supplementation on cancer incidence in older women: A randomized clinical trial. JAMA. 2017;317(12):1234-1243. doi:10.1001/jama.2017.2115

Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial [published correction appears in Am J Clin Nutr. 2008 Mar;87(3):794]. Am J Clin Nutr. 2007;85(6):1586-1591. doi:10.1093/ajcn/85.6.1586

Chen Y, Strasser S, Cao Y, Wang KS, Zheng S. Calcium intake and hypertension among obese adults in United States: associations and implications explored. J Hum Hypertens. 2015;29(9):541-547. doi:10.1038/jhh.2014.126

Myung SK, Kim HB, Lee YJ, Choi YJ, Oh SW. Calcium supplements and risk of cardiovascular disease: A meta-analysis of clinical trials. Nutrients. 2021;13(2):368. Published 2021 Jan 26. doi:10.3390/nu13020368

Kopecky SL, Bauer DC, Gulati M, et al. Lack of evidence linking calcium with or without vitamin D supplementation to cardiovascular disease in generally healthy adults: A clinical guideline from the National Osteoporosis Foundation and the American Society for Preventive Cardiology. Ann Intern Med. 2016;165(12):867-868. doi:10.7326/M16-1743

NIH Office of Dietary Supplements. Calcium fact sheet for health professionals.

Li K, Wang XF, Li DY, et al. The good, the bad, and the ugly of calcium supplementation: a review of calcium intake on human health. Clin Interv Aging. 2018;13:2443-2452. Published 2018 Nov 28. doi:10.2147/CIA.S157523

Thank you, {{form.email}}, for signing up.

There was an error. Please try again.