‌‌‌‌What is Calcium? 

Calcium constitutes 1.5 to 2% of total body weight making it by far the most abundant mineral in the body. Almost all of the calcium contained in the body is in the bones and teeth, but calcium is also found in the blood and other body tissues where it is important for the proper functioning of nerve cells, muscle contraction, regulation of heartbeat, and the clotting of blood. 

‌‌‌‌Why is Calcium Important for Bone Health?

Calcium serves several important functions in bone health. First, calcium provides the critical mineralization that bone needs to provide structural strength. The calcium in our bones also acts as a reservoir to ensure proper calcium levels in the blood are always maintained. 

Even though the calcium in the blood represents only a small percentage of the total calcium in the body, the body works extremely hard to maintain blood levels of calcium within a very narrow normal range. Bone is constantly remodeling (breaking down and rebuilding) all of the time in order to maintain blood levels of calcium within the normal range. 

The body automatically shifts calcium from the bones if a person is not ingesting enough calcium from either their diet or by supplementation. If the body continues to break down more bone than it replaces in order to maintain blood calcium levels, over time it can lead to osteoporosis, which literally translates to meaning porous bones. Osteoporosis reflects a lack of bone density.

Supplementation of calcium alone has been shown to be helpful in maintaining bone density, but it is more effective when it is combined with supplemental vitamin D3

‌‌‌‌Calcium, Bone Density, and Menopause

Building bone density by taking calcium and vitamin D3 supplements before menopause can help maintain bone density later in life. In other words, building strong bones and having sufficient bone density early in life helps prevent low bone density as a person gets older. Even if a woman waits till just before menopause to supplement with calcium and vitamin D3 it can lead to improvements in bone density and also slow down the rate loss in bone density by almost half compared to no supplementation of calcium and vitamin D3. If calcium and vitamin D supplementation isn’t started until after menopause it can still to help offset some of the age-related loss of bone density.1-5

‌‌‌‌What Forms of Calcium Are Available?

Calcium supplements are available in many different forms such as tablets, capsules, gummies, chewables including chocolates, and various liquid forms. Calcium carbonate is the most popular form of calcium used and for most people is totally fine, especially if it is taken with food. 6 However, in people that do not produce sufficient stomach acid or are taking acid-blocking drugs, taking a more easily ionized form such as calcium citrate or calcium bound to malate, aspartate, or lactate is recommended. These forms have some advantages over calcium carbonate because the calcium more easily releases from the carrier molecule. The problem with these forms of calcium is that the carrier molecules lead to greater bulk because they are larger than carbonate. So, it takes up to four times the number of tablets or capsules to provide the same level of elemental calcium when compared to products containing calcium carbonate. 

Advantages and Disadvantages of Different Forms Of Calcium




Calcium carbonate

Neutralizes stomach acid and in people that do not secrete enough stomach acid, it may not be as well absorbed. To produce maximum absorption, take with a meal. 

Inexpensive. Because it is less bulky than other forms, fewer capsules or tablets have to be taken. 

Calcium citrate; calcium bound to other Krebs cycle intermediates; calcium gluconate; calcium lactate

Since the carrier molecule is larger, more capsules or tablets have to be taken compared to calcium carbonate.

Best absorption on an empty stomach and can be absorbed easily even in those with an insufficient output of stomach acid. 

Calcium phosphate

May block the absorption of other minerals, especially iron.

Provides phosphate and does not lead to constipation.

Oyster shell calcium, dolomite, and bone meal

Can contain high levels of impurities, especially lead.


Microcrystalline calcium hydroxyapatite

More expensive and is not as well-absorbed compared to other forms.

Additional components may provide some other benefits in bone health.

‌‌‌‌Recommended Dosage of Calcium

The recommended range for supplementation of calcium for bone health is 600 to 1,200 mg per day. If there is a significant loss of bone density, the dosage should be at a higher level of 1,200 mg per day range. Going above this dosage level provides no additional benefits. 

Recommended Dietary Allowance for Calcium


0-0.5 year            400 mg

0.5-1 year            600 mg


1-3 years            800 mg

4-6 years            800 mg

7-10 years            800 mg

Young Adults and Adults

Males 11-24 years        1,200 mg

Males 25+ years        800 mg

Females 11-24 years    1,200 mg

Females 24+ years        800 mg

Pregnancy            1,200 mg

Lactating            1,200 mg

‌‌‌‌Possible Side Effects of Calcium

Calcium supplements generally do not produce side effects at recommended dosage levels. Higher dosages are not recommended as they may increase the risk for kidney stones and calcification of soft tissues outside the bone. 

‌‌‌‌Calcium Cautions and Warnings

Since some conditions, such as hyperparathyroidism, kidney disease, and cancer are associated with abnormalities in calcium metabolism, people with these disorders should consult a physician before taking a calcium supplement.

‌‌‌‌Calcium Drug Interactions

There are a number of drugs that calcium supplementation may reduce the absorption of including etidronate (Didronel®) and tetracycline antibiotics. Do not take calcium within two hours of taking these drugs. Calcium supplementation may also interfere with the action of the following drugs: phenytoin (Dilantin®), digoxin, and gallium nitrate (Ganite®). If you are taking any prescription drug, please consult your physician to determine any potential issues before taking a calcium supplement.


  1. Tai V, Leung W, Grey A, Reid IR, Bolland MJ. Calcium intake and bone mineral density: systematic review and meta-analysis. BMJ 2015;351:h4183.
  2. Jackson R, LaCroix A, Gass M, et al. for the Women’s Health Initiative Investigators: calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med 2006;354:669–683.
  3. Rizzoli R, Boonen S, Brandi ML, et al. The role of calcium and vitamin D in the management of osteoporosis. Bone 2008;42(2):246-9. 
  4. Boonen S, Vanderschueren D, Haentjens P, Lips P. Calcium and vitamin D in the prevention and treatment of osteoporosis - a clinical update. J Intern Med 2006;259(6):539-52.
  5. Quesada Gómez JM, Blanch Rubió J, Díaz Curiel M, Díez Pérez A. Calcium citrate and vitamin D in the treatment of osteoporosis. Clin Drug Investig. 2011;31(5):285-98
  6. Heaney RP, Dowell MS, Barger-Lux MJ. Absorption of calcium as the carbonate and citrate salts, with some observations on method. Osteoporos Int. 1999;9(1):19-23.