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Calcium is a nutrient that all living organisms need, including humans. Dietary sources of calcium include dairy products, green leafy vegetables, nuts, seeds, and fortified products.

Calcium is the most abundant mineral in the body. Humans need calcium to build and maintain strong bones, and 99% of the body’s calcium is in the bones and teeth. It is also necessary for maintaining healthy communication between the brain and other parts of the body. It plays a role in muscle movement and cardiovascular function.

Calcium occurs naturally in many foods, and food manufacturers add it to certain products. Supplements are also available.

Alongside calcium, people also need vitamin D, as this vitamin helps the body absorb calcium. Vitamin D comes from fish oil, fortified dairy products, and exposure to sunlight.

This article looks at why the body needs calcium, which foods are rich in calcium, what happens if the body does not have enough, and the pros and cons of taking supplements.

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Green leafy vegetables, such as broccoli, are a good source of calcium.

Calcium plays various roles in the body. These include the following:

Bone health

Around 99% of the calcium in the human body is in the bones and teeth. Calcium is essential for the development, growth, and maintenance of bone.

As children grow, calcium contributes to the development of their bones. After a person stops growing, calcium continues to help maintain the bones and slow down bone density loss, which is a natural part of the aging process.

Females who have already experienced menopause can lose bone density at a higher rate than males or younger people. They have a higher risk of developing osteoporosis, and a doctor may recommend calcium supplements.

Learn more here about osteoporosis.

Muscle contraction

Calcium helps regulate muscle contraction. When a nerve stimulates a muscle, the body releases calcium. The calcium helps the proteins in muscle carry out the work of contraction.

When the body pumps the calcium out of the muscle, the muscle will relax.

Cardiovascular system

Calcium plays a key role in blood clotting. The process of clotting is complex and has a number of steps. These involve a range of chemicals, including calcium.

Calcium’s role in muscle function includes maintaining the action of the heart muscle. Calcium relaxes the smooth muscle that surrounds blood vessels. Various studies have indicated a possible link between high consumption of calcium and lower blood pressure.

Vitamin D is also essential for bone health, and it helps the body absorb calcium. Find out more about vitamin D and why we need it.

Other roles

Calcium is a co-factor for many enzymes. Without calcium, some key enzymes cannot work efficiently.

Studies have also suggested that consuming enough calcium can result in:

  • a lower risk of developing conditions involving high blood pressure during pregnancy
  • lower blood pressure in young people
  • lower blood pressure in those whose mothers who consumed enough calcium during pregnancy
  • improved cholesterol values
  • a lower risk of colorectal adenomas, a type of non-cancerous tumor

Find out more here about the effects of having low calcium levels.

Further resources

For more in-depth resources about vitamins, minerals, and supplements, visit our dedicated hub.

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People can obtain calcium from a range of foods and drinks.

The following are good sources:

  • yogurt
  • milk
  • fortified dairy alternatives, such as soy milk
  • sardines and salmon
  • cheese
  • tofu
  • green leafy vegetables, such as broccoli, turnip leaves, watercress, and kale
  • many fortified breakfast cereals
  • fortified fruit juices
  • nuts and seeds, especially almonds, sesame, and chia
  • legumes and grains
  • cornmeal and corn tortillas

Some dark green vegetables, such as spinach, contain calcium. However, they also contain high levels of oxalic acid. Oxalic acid reduces the body’s ability to absorb calcium, according to studies.

Click here for some tips on getting enough calcium on a plant-based diet.

According to the Office of Dietary Supplements (ODS), people need the following amounts of calcium:

  • 0–6 months: 200 milligrams (mg)
  • 7–12 months: 260 mg
  • 1–3 years: 700 mg
  • 4–8 years: 1,000 mg
  • 9–18 years: 1,300 mg
  • 19–50 years: 1,000 mg
  • 51–70 years: 1,000 mg for males and 1,200 mg for females
  • 71 years and above: 1,200 mg

Pregnant and breastfeeding women require 1,000–1,300 mg depending on age.

A doctor may recommend additional calcium for people who:

The following conditions or lifestyle habits may result in low calcium levels, also known as hypocalcemia:

  • bulimia, anorexia, and some other eating disorders.
  • mercury exposure
  • overconsumption of magnesium
  • long-term use of laxatives
  • prolonged use of some medicines, such as chemotherapy or corticosteroids
  • chelation therapy used for metal exposure
  • lack of parathyroid hormone
  • people who eat a lot of protein or sodium may excrete calcium.
  • some cancers
  • high consumption of caffeine, soda, or alcohol
  • some conditions, such as celiac disease, inflammatory bowel disease, Crohn’s disease, and some other digestive diseases
  • some surgical procedures, including removing the stomach
  • kidney failure
  • pancreatitis
  • vitamin D deficiency
  • phosphate deficiency

The body eliminates some calcium in sweat, urine, and feces. Foods and activities that encourage these functions may reduce the levels of calcium in the body.

A doctor may recommend calcium supplements for people who have a calcium deficiency.

People who use calcium supplements should:

  • check first with their doctor whether they need supplements
  • follow the dosage the doctor recommends
  • take the supplement with food for best absorption and to minimize possible adverse effects
  • consume the supplements at intervals, usually two or three times a day

According to the ODS, around 43% of all adults in the United States take calcium supplements, including 70% of older females. Taking supplements can increase daily calcium intake by about 300 mg of calcium a day, on average.

Many calcium supplements also contain vitamin D. Vitamin D encourages the synthesis of proteins in the body and helps the body absorb calcium. Magnesium also plays a role in strengthening bones, and calcium supplements may also contain magnesium.

Types of supplement

There are different types of supplements. A doctor can recommend the best option. This will depend on the individual’s needs and preferences, any medical conditions they have, and whether they are taking any medications.

Elemental calcium is the pure mineral, but calcium in its natural form exists with other compounds.

Supplements may contain different proportions of calcium compounds and elemental calcium. For example:

Calcium carbonate: This contains 40% elemental calcium. This type is commonly available, and it is relatively cheap and convenient. A person should take it with food, as stomach acid helps the body absorb it.

Calcium lactate: This contains 13% elemental calcium.

Calcium gluconate: This contains 9% elemental calcium.

Calcium citrate: This contains 21% elemental calcium. A person can take it with or without food. It is useful for people with inflammatory bowel disease, achlorhydria, and some absorption disorders.

Research has found conflicting evidence regarding the benefits and drawbacks of supplement use.

Most experts agree that it is better to obtain nutrients from natural food sources, although sometimes it is not possible to get enough in this way.

Some studies have suggested, however, that calcium supplementation could be hazardous.

Side effects

Some people report gastrointestinal symptoms, such as bloating, constipation, gas, or a combination of all three when using calcium supplements.

Calcium citrate usually has fewer and less pronounced side effects than calcium carbonate. Taking the supplements with food, or spreading their intake throughout the day may help reduce the occurrence or intensity of the side effects.


Very high levels of calcium can lead to:

  • kidney problems
  • calcification of soft tissues and blood vessels
  • kidney stones
  • constipation

Although high calcium levels due to taking too many supplements might cause these severe side effects, they are more likely the result of cancer and thyroid problems, according to the ODS.

Possible complications

Past studies have raised concerns that taking calcium supplements may increase the risk of:

  • kidney stones
  • a reduction in iron absorption
  • a higher risk of a heart attack

However, more recent studies have suggested that these concerns may be unfounded.

Calcium may interact with some drugs. Experts make the following recommendations:

  • Take calcium supplements separately from some antibiotics.
  • Avoid supplement use while taking calcium channel blockers, which are a common type of medication for lowering blood pressure.

Calcium is essential for building and maintaining healthy bones and teeth. Among other roles, it may also help manage blood pressure.

It is best to obtain sufficient calcium through dietary sources, such as dairy products, green leafy vegetables, and tofu. However, a doctor may recommend supplementation for some people.

Due to individual differences in requirements, experts do not recommend calcium supplementation for everyone. Anyone who is considering taking supplements should ask their healthcare provider for advice.

Calcium supplements are available for purchase online.