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Everything You Need To Know About Calcium

Everything You Need To Know About Calcium
Reading Time: 5 minutes

What Is Calcium?

Calcium is a mineral, needed for strong bones and teeth as well as other important functions in the body. The World Health Organization has listed calcium on the List of Essential Medicines, and the US Food and Drug Administration has recommended a daily intake of 1000mg.[1] Other regulatory bodies, such as the Canadian Food Inspection Agency, have recommended a daily intake of 1100mg for persons two years of age and older and 500mg for infants and children less than two years of age.[2]

The majority (99%) of the calcium in the body is stored in the bones and teeth. The remainder (1%) is distributed throughout the body, in the blood, muscle tissues, and in the fluid between the cells.[3]

Calcium may be obtained from a variety of foods as well as from dietary supplements, with calcium carbonate and calcium citrate being the main forms. These supplements are used to prevent and treat calcium deficiency, which may result due to insufficient calcium intake. But because the body does not efficiently absorb more than 500mg at one time,[4] it’s recommended to take a 500mg dose twice a day rather than a one-time 1000mg dose.

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Facts About Calcium

  • Calcium is the most abundant mineral in the body.
  • The body uses bone calcium as a reservoir and constant source of calcium to maintain the correct concentration of calcium in the blood, muscle and intercellular fluids.
  • Calcium in the blood is used to regulate the pH of the body.
  • Vitamin D increases calcium absorption in the intestine.
  • Caffeine consumption tends to promote excretion (loss) of calcium in urine.
  • Vitamin K is integral in the regulation of calcium as well as formation of bones.
  • In women, calcium absorption reduces with age, as estrogen production decreases with age.
  • Calcium is lost from the body through sweat, urine, feces, hair, nails and skin cells.
  • Egg shells are a good source of calcium. (DIY calcium powder from eggshells)[5] [6] [8]
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Foods Containing Calcium

A variety of foods are rich in calcium, milk and milk products being the most well-known source. Fish with soft bones, such as sardines and salmon, are also an excellent source of calcium, as are nuts and seeds such as almonds, hazelnuts, sesame seeds and pistachios. Other foods include green leafy vegetables such as kale, broccoli, okra, dandelion leaves, watercress, kelp, wakame and beans (especially soy beans).

It should be noted however that some vegetables, though very rich in calcium, are also rich in other compounds which negatively affect the absorption of calcium. These vegetables include spinach, rhubarb, collard greens and chicory greens.

Some foods may be fortified with calcium and these include orange juice, soy milk, tofu, breakfast cereals and breads.

Calcium supplements are also excellent sources of calcium; the most common forms are calcium carbonate or calcium citrate. Each has varying amounts of elemental calcium, with calcium carbonate at 40% by weight and calcium citrate at 21%.

Other fundamental differences exist between these supplements, apart from the amount of calcium each contains.

  • Calcium carbonate is inexpensive and requires stomach acids for its absorption; therefore it is recommended to be taken with food.
  • Calcium citrate, on the other hand, may be taken with or without food, and is useful for persons with inflammatory bowel disease and absorption disorders.

Other forms of calcium supplements are calcium gluconate (9% elemental calcium) and calcium lactate (13% elemental calcium).[3] [7]

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Is Calcium Ever Bad For You?

Calcium is a very important mineral needed for various functions in the body. It is used for vascular contraction and vasodilation, to secrete hormones and enzymes, as well as to send messages through the nervous system. Even though this very vital mineral is needed for many bodily functions, care should be taken as to the amount that is ingested.

The following table shows the US recommended daily allowance (RDA) and the tolerable upper intake level (maximum intake level without any adverse effects) for various age groups:

Age/GenderUS RDATolerable Upper Intake
Infants less than 12 months200-260 mg1000-1500mg
Children 1-13 yrs700-1300 mg2500 mg
Young adults 14-18 yrs1300 mg3000 mg
Pregnant/Lactating 14-18 yrs1300 mg3000 mg
Men/Women 19-50 yrs1000 mg2500 mg
Pregnant/Lactating 19-50 yrs1000 mg2500 mg
Men 51-70 yrs1000 mg2000 mg
Women 51-70 yrs1200 mg2000 mg
Men/Women 71 yrs+1200 mg2000 mg


Health risks associated with the over-intake of calcium include poor functioning of the kidneys, hardening in vascular and soft tissue due to an accumulation of calcium salts, high levels of calcium in the urine, and kidney stones. Other risks associated with excessive calcium intake are constipation and the formation of tumors or cancer. [4]

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Benefits of Calcium 

Calcium has many health benefits and has been associated with the prevention and treatment of several diseases, chief among which is Osteoporosis, a disorder characterized by porous and fragile bones. Osteoporosis is mostly associated with fractures of the hips, vertebrae, pelvis, ribs and other bones. Regular exercise and adequate intake of calcium and vitamin D are effective in ensuring healthy bone formation and maintenance throughout the body cycle, hence reducing the risk of Osteoporosis and its symptoms.

Calcium reduces the risk of Preeclampsia, a condition in which pregnant women develop hypertension (high blood pressure) and proteinuria (kidney damage). The American College of Obstetrics and Gynecology (ACOG) and the World Health Organization (WHO) have recommended an intake of 1500-2000mg in the form of calcium supplements in order to reduce the risk of Preeclampsia.

Other benefits of calcium include reduced risks of colon and rectal cancer, cardiovascular disease, and tooth loss. Studies indicate that calcium intake from foods and/or supplements are associated with a reduced risk of colon cancer. Calcium has been successful in the reduction of cardiovascular disease by decreasing intestinal absorption of lipids, increasing lipid excretion, lowering cholesterol levels in the blood and promoting movement of calcium into the cells.[4]

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Negative Impact Of Calcium On The Body

Side effects of calcium intakes are generally mild, as long as the tolerable upper limit is not exceeded. Calcium may cause minor side effects such as gas or constipation.

Other major health risks may result from excessive intake of calcium, and these include formation of kidney stones and cancer of the prostate. Studies indicate a positive correlation between high calcium intakes from supplements and the increased risk of kidney stones. Calcium intakes of over 2000mg have shown a positive correlation to increased risk of prostate cancer.

The calcium obtained from foods has no adverse effects, as even calcium-rich foods contribute only up to 30% of the daily value, so a variety of foods have to be consumed in order to obtain the recommended daily value of 1000mg. Adverse reactions are more associated with calcium supplements, excessive intake and interactions with other drugs. Minimizing one’s intake of calcium supplements, as well as antacids such as Tums or Rolaids (which provide between 200 – 400mg of calcium), will minimize the risk of calcium overdose.[3] [4]

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Should You Worry About Calcium?

There are relatively few concerns associated with calcium intake. However, for persons who are intolerant to certain calcium sources, problems may arise due to their sensitivity to the actual source of the calcium.

In addition, calcium does interact adversely with several prescription medications, and care should be taken if you are taking them for other ailments. Calcium decreases the absorption of medications such as:

  • Bisphosphonates, used to treat osteoporosis,
  • The fluoroquinolone and tetracycline classes of antibiotics,
  • Levothyroxine, used to treat thyroid issues,
  • Phenytoin, an anti-seizure drug, and
  • Tiludronate disodium, used to treat Paget’s disease.

Other interactions include:

  • Thiazide-type diuretics with calcium carbonate and vitamin D, increasing the risk of hypercalcemia and hypercaliuria.
  • Antacids containing magnesium and aluminum increase urinary calcium excretion,
  • Mineral oil and stimulant laxatives decrease calcium absorption.

Finally, glucocorticoids such as prednisone may cause depletion of calcium, leading to osteoporosis after prolonged exposure.[5] [6]

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Final Thoughts

Calcium obtained from natural food sources poses little or no health risk and plays a vital role in the proper functioning of the body and in the prevention and treatment of various diseases. Calcium supplements, however, should be taken with care to avoid excessive intake leading to various complications, as well as interactions with certain medications. It is recommended that supplementary intake not exceed the daily value for each age group and stage, and due diligence must be paid when treating other conditions with drugs that may interact with calcium. As with all supplements, check with your doctor before adding them to your diet or changing the dosage.