All You Need to Know about Calcium Supplements

May 2021

Which is the Best Calcium Supplement?

Check out our unbiased recommendation of the best products on the market using our rigorous methodology. We screen products for the right formulation, bioavailability, safety, and efficacy to bring you only the best supplements available in 2019.

A Closer Look at Calcium

Why Calcium is Crucial for Health

Calcium is the most abundant mineral in the human body — and 99% of that calcium is found in the bones and teeth. There is consensus in the scientific community that adequate calcium intake is crucial for children and adolescents in order to build strong bones, and for older adults in order to maintain bone density and prevent osteoporosis.[1] Furthermore, calcium is necessary for the proper functioning of the heart, nerves, muscles, hormones, and other bodily systems.[2]

Building up bone mass with minerals is essential for avoiding osteoporosis later in life, and for reducing the risk of fractures from falls. It is especially important for children, adolescents, young adults, and the elderly to consume adequate amounts of calcium, in order to build up strong bones early in life and maintain bone strength later on. Calcium is also needed throughout the body for various metabolic processes; your bones and teeth essentially serve as a reservoir for the calcium that is needed elsewhere.[1, 5]


Older individuals, particularly postmenopausal women, are particularly likely to have low levels of calcium.[3, 4] In older adults, bone breakdown occurs at a higher rate than bone formation, leading to bone loss.[5] Calcium deficiency can lead to osteoporosis, a disease that is characterized by low bone mass and bone fragility. The bone tissue deterioration caused by osteoporosis can greatly increase the likelihood of fractures from falls.[3] An estimated 10 million Americans suffer from osteoporosis, and 80% of them are women. A further 34 million Americans suffer from osteopenia, which is the precursor to osteoporosis and is characterized by low bone mass.[5] Some research has indicated that hormone replacement therapy with estrogen and progesterone can promote the absorption of calcium and offset the rate of bone loss caused by the onset of menopause. Additionally, an active lifestyle involving both weight-bearing and resistance exercise can help to develop strong bones and reduce the risk of osteoporosis later in life.[5]

Childhood and adolescence is the most crucial time for promoting bone formation, as this process levels off during adulthood. Although it is unusual for children to be noticeably deficient in calcium, this age group can benefit dramatically from consuming the recommended daily allowance of calcium.[5]

Certain illnesses can also contribute to calcium deficiency, such as Crohn’s disease and celiac disease. Individuals who consume large amounts of protein, caffeine, sodium, or alcohol may also be at risk for calcium deficiency, as are people taking corticosteroid medications.[2]

Individuals who are lactose intolerant, as well as vegans and some vegetarians, may not be ingesting sufficient levels of calcium due to their avoidance of calcium-rich dairy products. These individuals should consider consuming dairy products that are low in lactose (such as aged cheeses, yogurt, and lactose-free milk), as well as calcium-fortified foods and dark, leafy vegetables, or taking a calcium supplement.[5]

If you do choose to take a calcium supplement, or are generally concerned about your bone health, it is vital to have sufficient levels of vitamins K and D in the body. We recommend choosing a supplement regimen that includes adequate amounts of both vitamins for proper processing and storage of calcium.

Benefits of Calcium

The most well-known benefit of calcium is the role it plays in building strong bones, thus reducing the risk of osteoporosis, fractures, and falls later in life. Studies have shown that both dietary calcium and calcium supplements can increase bone density and mass.[6] Because nearly all of the body’s calcium is stored in the bones and teeth, ingesting the recommended amount of calcium helps to contribute to their structure and hardness.[7] Bone mass peaks around the age of 30, which means that individuals with a greater peak bone mass can delay the subsequent process of bone deterioration. The deterioration process accelerates with age, so maintaining adequate calcium intake is necessary in order to avoid significant bone loss.[2, 5]

For individuals with hypoparathyroidism (underactive parathyroid gland), many doctors will recommend a diet that is high in calcium and low in phosphorus, perhaps in conjunction with calcium and vitamin D supplementation.[2]

The effect of calcium on cardiovascular health has been the subject of much scientific debate. Although calcium is undoubtedly necessary for the circulatory system to properly function, there is some disagreement about the recommended amount of daily calcium intake, and whether calcium supplements can have an adverse effect on cardiovascular health. Although research has suggested that calcium intake can improve lipid profiles and lower cholesterol, excessively high calcium intake may sometimes lead to coronary heart disease and myocardial infarctions.[5]

Calcium (either from food sources or supplementation) has been associated with lowering both systolic and diastolic blood pressure, due to the fact that it regulates the body’s sodium-potassium balance. Research has suggested that consumption of calcium from dairy products, together with a diet rich in fruit and vegetables, can decrease the risk of hypertension.[7]

Some studies have found links between calcium intake and the prevention of premenstrual syndrome. Others have suggested that dietary calcium may decrease the risk of high blood pressure and preeclampsia during pregnancy.[2]

Several studies have proposed a link between adequate calcium intake and the prevention of colon and rectal cancers; however, further long-term research is needed before conclusive recommendations can be made. Some doctors do recommended calcium supplementation as a preventative measure against colorectal cancers. Conversely, some studies have suggested that daily calcium intake of between 1,500 and 2,000 mg may actually increase the risk of prostate cancer; clearly, more research is needed.[5]

Calcium has been linked with the prevention and treatment of many other health conditions, including high cholesterol and high triglyceride levels, strokes, and obesity. However, more research is needed to investigate the relationship between calcium intake and these conditions.

Internal Processing of Calcium

The 1% of calcium in the body that is not used for building strong bones and teeth is used to facilitate a variety of metabolic functions, including muscle contraction, nerve transmission, and intracellular signaling.[1] It is also required for blood circulation and to help release hormones and enzymes that are needed throughout the body.[7] The human body uses the calcium stored in bones and teeth as a reservoir in order to maintain a constant level of calcium in blood, muscle, and intracellular fluids.[5]

Vitamin D, which can be obtained from certain foods and dietary supplements, as well as produced through sun exposure, increases the absorption of calcium in the small intestine.[7] Along with parathyroid hormone, vitamin D regulates calcium homeostasis, determining how much calcium is deposited into bones and teeth and how much is present in intracellular fluids, plasma, soft organs, and tissues.[9] Vitamin K, magnesium, and phosphorus also promote calcium absorption.[2] On the other hand, phytic acid and oxalic acid will bind to calcium, thus inhibiting absorption. Foods that are high in these acids are spinach, collard greens, rhubarb, and beans, as well as whole-grains, seeds, and nuts. However, as part of a balanced diet, these foods will have very little overall impact on calcium absorption. On the other hand, research has shown that excessive consumption of protein, alcohol, caffeine, and sodium may prevent calcium from being properly absorbed.[5]

Age has a major impact on how much calcium the body absorbs; older individuals are able to absorb much less calcium than younger people. Infants and children are able to absorb as much as 60% of the calcium they consume, as it is so necessary for building up their bones. However, adults absorb only 15% to 20% of the calcium they consume, and this absorption percentage continues to decrease with age.[5]

Getting to Optimal Calcium Levels

Food Sources

Food sources are certainly the best way to get calcium into your body. Dairy foods such a milk, yogurt, and cheese can provide the body with significant amounts of calcium. Calcium is also found in collard greens, broccoli, broccoli rabe, kale, Swiss chard, bok choy, soy beans, tofu, almonds, hazelnuts, and figs. Many food products can also be fortified with calcium, most commonly orange juice, soy/rice/almond milk, breakfast cereals, pasta, and bread products. Soft-boned fish such as canned sardines and salmon can also provide dietary calcium.[7]


Like magnesium, calcium is an ion, so it must be consumed as part of a compound. The most common calcium supplements are calcium carbonate and calcium citrate, although it is available in many other forms, such as calcium gluconate, calcium lactate, and calcium phosphate.

Calcium carbonate is probably the most widespread and inexpensive calcium supplement; it is usually available in doses of around 600 mg and should be taken with food or a glass of juice to promote its absorption.[7] Calcium carbonate actually contains more elemental calcium than calcium citrate and it is often found in antacids such as Tums and Rolaids.[2]

Calcium citrate supplements can be taken with or without food and may be a better option for those who struggle to absorb enough calcium, as well as individuals with achlorhydria or inflammatory bowel disease. This form is usually more expensive than calcium carbonate supplements. Calcium citrate should not be combined with antacids.

Calcium and vitamin D are often combined into a single supplement because vitamin D helps to increase calcium absorption and is also crucial for bone strength and muscle function. Some calcium supplements may also combine calcium with magnesium or vitamin K.

Calcium supplements are a useful method to complement calcium intake from food. To prevent osteoporosis, older adults should maintain a total calcium intake, from both food and supplementation, of between 1,000 and 1,200 mg/day, depending on age, gender, and medical history.[4] However, based on a typical western diet, the average calcium intake for this age group is only about 700 – 900 mg/day.[1, 6] Calcium supplements and calcium-fortified foods can help people reach the suggested daily intake. However, caution should be taken when deciding on a dose for calcium supplementation, as certain studies have suggested that an average daily intake of more than 1,200 mg can be harmful to cardiovascular health.[4]

Most calcium supplements contain around 500 to 600 mg of elemental calcium, bonded as part of a variety of different compounds, such as calcium carbonate and calcium citrate. Some research indicates that a dose of 500 mg promotes optimal calcium absorption, but this depends on age and other factors.[5]

Proper Dosage and Contraindications

Consuming too much calcium, either from food, supplementation, or both, can cause hypercalcemia. Medical professionals have documented this as a real risk, labelling it “calcium supplement syndrome.” Although too much dietary calcium can theoretically cause hypercalcemia, this disorder is particularly prevalent among individuals who indiscriminately ingest calcium and vitamin D supplements. Vitamin D helps the body to absorb calcium and can thus exacerbate the problems linked with excessive calcium intake.[10] Urine and blood tests can indicate whether an individual is hypercalcemic. High vitamin D levels are not too likely but are also indicative of this condition.[11]

Before beginning a calcium supplement regimen, it is a good idea to speak to your doctor first, as there can be severe consequences for ingesting too much or for combining excessive calcium with certain medications. Your doctor will be able to advise you about the proper dosage based on your age, gender, and medical history.

Some studies have indicated that excessive calcium intake, particularly from calcium supplementation, can increase the risk of cardiovascular disease and even cardiovascular mortality.[12] Some research has suggested that 1,200 mg per day of calcium is the maximum threshold before cardiovascular health is negatively impacted, while other research has suggested a higher threshold of 1,500 mg per day. Certain studies have indicated that adults over the age of 65 can safely ingest up to 1,500 mg of calcium per day (as a combination of food and supplementation), while younger adults can safely ingest up to 1,200 mg per day.[1, 4]

Currently, the Institute of Medicine recommends that children from 1 to 3 years old should consume 700 mg of calcium a day; children 4 to 8 years old should consume 1,000 mg of calcium a day; and adolescents 9 to 18 years old should consume 1,300 mg of calcium a day. The Institute of Medicine recommends a daily intake of 1,000 mg for women ages 19-50 and men ages 19-70. Women over age 50 and men over age 70 should consume 1,200 mg per day.[2] However, more research is needed to determine the health effects of consuming more calcium than these recommended amounts, and whether there is any difference between the effects from calcium in food versus calcium supplements. The Institute of Medicine acknowledges that the tolerable upper limit of daily calcium intake for adults may be as much as 2,500 mg of calcium per day, but this is likely to have negative impacts on cardiovascular health in some cases.

If you choose to complement a healthy diet with a calcium supplement, you should generally avoid taking more than 500 mg of calcium at one time, to avoid potential side effects. Side effects are commonly digestive distress, ranging from stomach upset, constipation, to gas and bloating. If these side effects occur, consider taking the supplement along with food, making sure that you are drinking 6 to 8 glasses of water per day, spreading out the dose throughout the day, or switching to another brand or form of calcium supplement.

Individuals who are already at risk for cardiovascular disease should pay particular attention to their calcium intake. Cardiovascular disease risk factors include diabetes, obesity, high blood pressure, and dyslipidemia. Individuals with cancer, hyperparathyroidism, kidney failure, and sarcoidosis are also at risk for having high levels of calcium. Hypercalcemia due to excessive calcium and/or vitamin D intake has also been linked to kidney problems, including an increased risk of developing kidney stones and poor kidney function.[13] The composition of kidney stones is 80-90% calcium, in the form of calcium oxalate or calcium phosphate.[14] People with a history of kidney stones should not take calcium supplements and should discuss their dietary intake of calcium with their doctor. In rare cases, excessive calcium intake can lead to altered mental states. Additionally, calcium carbonate has been linked to dyspepsia and diarrhea.

Drug Interactions

Because calcium is involved in so many bodily processes, certain medications can have a wide range of adverse (and sometimes contradictory) reactions when taken alongside calcium supplements. Certain medications may reduce the effectiveness of calcium supplements, while others may cause excessive, unhealthy calcium absorption or other toxic effects such as kidney damage.

Medications in the class Biphosphonates are used to treat osteoporosis and similar diseases. Calcium supplements may interfere with the body’s absorption of biphosphonates such as alendronate (Fosamax), etidronate (Didronel), ibandronate (Boniva), risedronate (Actonel), tiludronate (Skelid), and zoledronic acid (Reclast). Calcium supplements should be taken at least two hours before any type of biphosphonate.

Certain types of cholesterol-lowering medications, such as cholestyramine (Questran), colestipol (Colestid), and colesevelam (Welchol), may cause excess calcium to leave your body in your urine, creating the need for calcium supplementation. Some anti-seizure medications, such as phenytoin (Dilantin), carbamazepine (Tegretol), phenobarbitol, and primidone (Mysoline) can also cause lowered calcium levels. Calcium supplements and anti-seizure medications should be taken two hours apart so they do not interfere with each other’s absorption; taking vitamin D along with anti-seizure medications may also help to keep calcium levels up. Calcium may also interfere with blood pressure medications; always talk to your doctor before combining a calcium supplement with a beta-blocker or a calcium channel-blocker.

Calcium can interfere with the body’s ability to absorb certain antibiotics, including quinolone antibiotics such asiprofloxacin (Cipro), levofloxacin (Levaquin), norfloxacin (Noroxin), and ofloxacin (Floxin), and other antibiotics such as doxycycline, minocycline, and tetracycline. Calcium supplements should be taken two to four hours before or after ingesting these antibiotics. Furthermore, the antibiotics gentamicin (Garamycin) and ceftriaxone (Rocephin) may have dangerous reactions when combined with calcium supplements.

Calcium citrate increases the body’s absorption of aluminum, so it should not be taken along with any aluminum-containing antacid; it could cause toxic aluminum levels for people with kidney disease. Taking calcium supplements along with calcipotriene (Dovonex), a topical medication used to treat psoriasis, may cause excessively high levels of calcium — hypercalcemia.

Certain diuretics will cause calcium levels in the blood to rise, while others will cause calcium levels to fall, so calcium intake should be monitored closely when taking diuretics. On the other hand, digoxin (Lanoxin, Digox), a medication used to treat irregular heart rhythms, needs the correct amount of calcium in the blood in order to be safe and effective; too much calcium may cause a toxic reaction, while too little calcium may prevent the medication from working. Calcium can decrease the amount of thyroid hormone that the body can absorb, and it can also decrease the absorption of sotalol (Betapace), another medication used to treat irregular heartbeat.[2, 5]

Choosing a Calcium Supplement

Most people are able to get their recommended daily allowance of calcium from eating calcium-rich and calcium-fortified foods, and there is no reason to take a supplement if you are already meeting your dietary needs for calcium. But for individuals who are vegan or lactose-intolerant, a calcium supplement can provide the calcium missing from the diet.[15] Calcium supplements may also be a good option for individuals with osteoporosis, inflammatory bowel disease, or celiac disease, as well as people who take corticosteroids or who have a high-protein, high-sodium diet.[16] You should consult with your doctor before starting a calcium supplement regimen.

Calcium carbonate is the cheapest and most ubiquitous form of calcium supplement and it is an effective source of calcium for most people. Those who struggle to absorb enough calcium or who have gastrointestinal issues should consider calcium citrate or another form.[16] When purchasing a calcium supplement, it is important to realize that different calcium compounds contain different amounts of elemental calcium — the calcium that is actually absorbed during digestion. Calcium carbonate contains the largest amount of elemental calcium (about 40% of calcium carbonate is composed of elemental calcium), while calcium citrate contains 21% elemental calcium. Calcium lactate and calcium gluconate contain 13% and 9% elemental calcium, respectively. All of the doses and amounts mentioned in this article refer to elemental calcium. You should always read supplement labels to ensure that you understand how much elemental calcium is contained in the supplement, as opposed to the total compound amount.

Calcium supplements come in a variety of forms, including chewable and effervescent tablets and gel capsules, and they are available for purchase online and off-the-shelf from pharmacies and supermarkets. Calcium carbonate should always be taken with food, although calcium citrate, calcium gluconate, and calcium lactate can be taken by themselves. Antacids like Tums and Rolaids both contain calcium carbonate as a key ingredient. Many calcium supplements are combined with vitamin D, which increases calcium absorption. This is usually beneficial, but it also requires consumers to monitor both their calcium and vitamin D intake from other sources, in order to avoid excessive intake. It is best to take calcium in small doses, generally no more than 500 mg at one time.[16]

Read the ingredients listed on the label and always avoid calcium supplements that are derived from oyster shells, dolomite, or bone meal. Supplements made from these sources may contain lead which is toxic to the brain and kidneys.[2]

There is evidence that vitamin K and vitamin D can work together with calcium to improve bone health. One human study found that adding vitamin K to supplements containing vitamin D and calcium improved bone mineral density more than just taking vitamin D and calcium alone.[17] As a result, if you do choose to supplement calcium or are concerned about your bone health, consider a supplement regimen that contains vitamins K and D.

The recommended calcium products passed our very stringent analysis for high quality calcium supplementation. Read more about our methodology for selecting recommended products.

Which is the Best Calcium Supplement?

Check out our unbiased recommendation of the best products on the market using our rigorous methodology. We screen products for the right formulation, bioavailability, safety, and efficacy to bring you only the best supplements available in 2019.

1 Wang, Lu, JoAnn E. Manson, and Howard D. Sesso. “Calcium Intake and Risk of Cardiovascular Disease: A Review of Prospective Studies and Randomized Clinical Trials.” American Journal of Cardiovascular Drugs. (2012) 12(2): 105–116. doi:10.2165/11595400-000000000-00000.
2 “Calcium.” University of Maryland Medical Center. June 2014.
3 Ethgen, Olivier, Mickaël Hiligsmann, Nansa Burlet, and Jean-Yves Reginster. “Public health impact and cost-effectiveness of dairy products supplemented with vitamin D in prevention of osteoporotic fractures.” Archives of Public Health. (2015) 73:48.
doi 10.1186/s13690-015-0099-3.
4 Kim, Kyoung Min, Han Seok Choi, Mi-Ja Choi, and Ho Yeon Chung. “Calcium and Vitamin D Supplementations: 2015 Position Statement of the Korean Society for Bone and Mineral Research.” Journal of Bone Metabolism. (2015) 22:143-149.
5 “Calcium: Dietary Supplement Fact Sheet.” National Institutes of Health: Office of Dietary Supplements. February 2016.
6 Tai, Vicky, William Leung, Andrew Grey, Ian R Reid, and Mark J Bolland. “Calcium intake and bone mineral density: systematic review and meta-analysis.” The BMJ. (2015) 351:h4183. doi:10.1136/bmj.h4183.
7 “Calcium: Fact Sheet for Consumers.” National Institutes of Health: Office of Dietary Supplements. March 2013.
8 Waldman, Talya, Raheleh Sarbaziha, Noel Bairey Merz, and Chrisandra Shufelt. “Calcium Supplements and Cardiovascular Disease: A Review.” American Journal of Lifestyle Medicine. (2015) 9(4): 298–307. doi:10.1177/1559827613512593.
9 Rzymski, Pawel, Ivo Pischel, Frank Conrad, Thomas Zwingers, Piotr Rzymski, Tomasz Opala. “The bioavailability of calcium in the form of pyruvate, carbonate, citrate–malate in healthy postmenopausal women.” European Food Research and Technology. (2016) Vol. 242, Issue 1, p. 45-50. doi: 10.1007/s00217-015-2516-9.
10 Machado, Maria, Araba Bruce-Mensah, Melanie Whitmire, Ali A. Rizvi. “Hypercalcemia Associated with Calcium Supplement Use: Prevalence and Characteristics in Hospitalized Patients.” Journal of Clinical Medicine. (2015) 4(3): 414–424. doi: 10.3390/jcm4030414.
11 Singh, Ashutosh and Ambika Ashraf. “Hypercalcemic crisis induced by calcium carbonate.” Clinical Kidney Journal. (2012) 5(4): 288–291. doi: 10.1093/ckj/sfs060.
12 Xiao, Qian, Rachel A Murphy, Denise K. Houston, Tamara Harris, Wong-Ho Chow, and Yikyung Park. “Dietary and supplemental calcium intakes in relation to mortality from cardiovascular diseases in the NIH-AARP Diet and Health Study.” JAMA Internal Medicine. (2013) 173(8): 639–646. doi:10.1001/jamainternmed.2013.3283.
13 “Balancing the benefits and risks of calcium supplements.” Health News and Evidence. 14 March 2013.
14 Sorensen, Matthew D. “Calcium intake and urinary stone disease.” Translational Andrology and Urology. (2014) 3(3): 235–240. doi: 10.3978/j.issn.2223-4683.2014.06.05.
15 “How Do I Know if I Need A Calcium Supplement?” Osteoporosis Canada.
16 “Who Should Consider Calcium Supplements?” Mayo Clinic. August 2015.
17 Je SH, Joo N-S, Choi B, Kim K-M, Kim BT, Park S-B, Cho D-Y, Kim KN, Lee D-J. “Vitamin K Supplement Along with Vitamin D and Calcium Reduced Serum Concentration of Undercarboxylated Osteocalcin While Increasing Bone Mineral Density in Korean Postmenopausal Women over Sixty-Years-Old.” J Korean Med Sci. 2011 Aug; 26(8):1093–1098. doi: 10.3346/jkms.2011.26.8.1093. Accessed through: