Calcium is the most abundant mineral in the body. 99% of the total calcium is stored in the teeth and bones. The rest is found in the bloodstream where it is involved in muscle function, especially the heart, and in muscle control by the nerves. It also plays a role in receiving hormonal messages and blood clotting. 

Bone strength and rigidity is due in large part to calcium (in the presence of magnesium and phosphorus). 

However, the body can draw calcium from the bones, causing bone fragility. 


What does calcium do? 

Calcium’s main purpose in the body is to form bone and tooth structure. Calcium also plays a role in: 

  • Regulating heartbeat;
  • Contracting and relaxing muscles;
  • Regulating blood pressure;
  • Clotting blood;
  • Healing injuries;
  • Transmitting the brain’s messages to various parts of the body.


Adequate Intake (AI)* of Calcium: 

Amount (mg or/UI*)
0 to 6 months
7 to 12 months
1 to 3 years
4 to 8 years
Preteens and teens
9 to 18 years
1 300mg (1.3g)
19 to 50 years
1 000mg (1g)
50 and up
1 200mg (1.2g)

Source: Institute of Medicine, Food and Nutrition Board, Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride, 1997.

*Lacking sufficient scientific evidence, authorities have established adequate intake (AI) amounts rather than recommended dietary allowances (RDAs). With regard to calcium in particular, it is very difficult to estimate the intake that will allow for optimal accumulation and retention because a number of other factors affect bone health, including genes, hormones, and physical activity, among others. Adequate calcium intake is based on observed average intakes in North Americans in good health.


Dairy products are the best food sources for calcium. Canned fish is also a good source. Green leafy vegetables like broccoli and cabbage also provide calcium, but in lesser quantity. The calcium in legumes, nuts, and grains is less well absorbed by the intestines than that found in dairy products. Creamy cheeses generally contain less calcium than firm cheeses.

Absorption of the calcium from food depends on what else is eaten at the same meal: 

  • Vitamin D increases calcium absorption;
  • Bran cereals and spinach decrease calcium absorption;
  • Caffeine and protein-rich diets increase calcium loss through the urine.

Food Sources for Calcium: 

Firm tofu made with calcium sulfate
100g (0.75oz)
Emmental, Romano, Gruyère, and Parmesan cheeses
50g (1.5oz)
Soy beverage, enriched
250ml (1 cup)
Ricotta cheese, part skim
125ml (0.5 cup)
Brick, cheddar, Edam, Gouda, provolone, Roquefort, and Swiss cheeses
50g (1.5oz)
Regular tofu made with calcium salt
100g (0.75oz)
Canned sardines, with bones
100g (0.75oz) (8 average sardines)
Goat’s milk
250ml (1 cup)
Cow’s milk, 0% to 3.25% M.F.
250ml (1 cup)
Plain yogurt, 0% to 3.25% M.F.
175ml (3/4 cup)
Blue, Camembert, feta, and mozzarella cheeses
50g (1.5oz)
Canned salmon, with bones
100g (0.75oz)
Black-eyed peas, cooked
250ml (1 cup)
Sesame seeds, unhulled
18g (30ml – 2 tbsp)
Orange juice, calcium enriched
125ml (0.5 cup)
Atlantic perch, grilled
100g (0.75oz)
Tofu made with magnesium salt
100g (0.75oz)
Canned clams
100g (0.75oz)
Chinese cabbage, boiled
125ml (0.5 cup)
28g (23 almonds)


The North American diet typically provides less calcium than the recommended intakes. The percentage of empty calories and processed foods in modern diets and the inadequate consumption of fruits and vegetables are likely the cause. 

Calcium deficiency in growing children and adolescents may prevent them from achieving optimal bone mass. Individuals with vitamin D deficiency or chronic kidney failure may have abnormally low blood calcium levels. 

Calcium is not well absorbed without the presence of vitamin D. In those over 65, a 400 to 600 IU/day vitamin D supplement is recommended for its beneficial effect on calcium balance and hence bone mineralization. This supplementation is even more important given that the skin’s production of vitamin D decreases with age and less frequent sun exposure.  

Calcium deficiency can only be diagnosed through laboratory tests. Observable external signs will only become apparent after a very long time. 

Signs of calcium deficiency:

  • Osteoporosis (very low bone mineral density);
  • Osteopenia (lower than normal bone mineral density);
  • Increased risk of fractures;
  • Dentition and gum problems;
  • Kidney disease;
  • Hyperparathyroidism;
  • Abnormal heartbeat;
  • Nervousness, agitation;
  • Cramps;
  • Depressionp;
  • Brittle nails;
  • Eczema.

Some people with greater calcium requirements may benefit from taking a supplement:

  • Postmenopausal women;
  • Women of childbearing age and pregnant and nursing women;
  • Those who consume few or no dairy products;
  • Lactose intolerant individuals;
  • Anorexics and bulimics;
  • Women who have had their ovaries removed or undergone early menopause (before the age of 45);
  • High performance athletes;
  • Excessive smokers;
  • Those who consume too much alcohol, coffee, tea, cola, or salt.

Adverse effects

Signs of excess calcium (at doses higher than 2,500 mg/day):

  • Kidney stones;
  • Hypercalcemia and kidney failure;
  • Interference of calcium with the absorption of other minerals;
  • Muscle and bone pain;
  • Nausea and vomiting;
  • Confusion;
  • Constipation, intestinal gas, burping;
  • Headaches.

Increased vitamin D in our bodies may produce a rise in blood calcium levels and lead to heart abnormalities as well as calcium deposits in the kidneys.


You should consult a physician or pharmacist before taking calcium supplements if you: 

  • Suffer from kidney failure;
  • Take thiazide-type diuretics;
  • Have a low intake of minerals that interact with calcium;
  • Suffer from chronic constipation;
  • Suffer from sarcoidosis (a rare disease that mainly attacks the skin and lymph nodes).


Signs of excess calcium (at doses higher than 2,500 mg/day):

Natural health products or vitaminic supplements: 

  • Calcium may interfere with the absorption of iron, zinc, chromium, and manganese.*
    *Ensure you wait two hours between taking calcium and any of these minerals.


A number of medications must be taken two hours before or after a calcium supplement, including:

  • Antibiotics with quinolone and tetracycline derivatives;
  • Bisphosphonates (e.g., Fosamax®, Actonel®);
  • Thyroid hormones.

Calcium requirements may increase when the following medications are taken (nonexhaustive list—consult a physician or pharmacist): 

  • Thiazide diuretics;
  • Anticonvulsants;
  • Corticosteroids;
  • Antituberculosis drugs;
  • Heparin.

Calcium combined with high doses of vitamin D may interfere with heart and blood pressure medications.

Additional information

***Speak with your pharmacist if you plan to take calcium supplements. Your pharmacist can help you choose the solution that’s best for you based on your health and any drugs you take. 

Other names

Calcium, Ca, calcium acetate, Calcium aspartate, calcium carbonate, Chelated calcium, calcium chloride, Calcium citrate, calcium citrate malate, Calcium gluconate, calcium lactate, Calcium lactate gluconate, Calcium orotate, calcium phosphate, Dolomite, Bone powder