Calcium is a chemical element that is essential for living organisms, including humans. It is the most abundant mineral in the body and vital for good health.

We need to consume a certain amount of calcium to build and maintain strong bones and healthy communication between the brain and other parts of the body. Calcium is found naturally in many foods; it is also added to certain products, and supplements are available.

In this article, we explain why the body needs calcium, which foods are rich in calcium, and what happens if the body does not have enough.

Fast facts on calcium

  • Calcium is vital for bone health.
  • Vitamin D helps the body absorb and retain calcium.
  • Milk, broccoli, and tofu are just some of the foods rich in calcium.
  • Calcium supplements can produce side effects, such as bloating and gas.
  • Some dark green vegetables contain high levels of oxalic acid, which can reduce the body's ability to absorb calcium.

Why do we need calcium?

Calcium plays a range of roles in the body; these include:

Bone health

A range of food sources provide calcium.

Around 99 percent of the calcium in the human body is found in the bones and teeth; it is essential for the development, growth, and maintenance of bone. Calcium continues strengthening the bones of humans until they reach the age of 20-25 when bone density is highest. After that age, bone density declines, but calcium continues to help maintain bones and slow down bone density loss, which is a natural part of the aging process.

People who do not consume enough calcium before the age of 20-25 have a considerably higher risk of developing brittle bone disease or osteoporosis later in life; this is because calcium is drawn from the bones as a reserve.

Muscle contraction

Calcium regulates muscle contraction, including the beating of the heart muscle. When a nerve stimulates a muscle, calcium is released; it helps the proteins in muscle carry out the work of contraction. The muscle only relaxes again once the calcium is pumped back out of the muscle.

Blood clotting

Calcium plays a key role in normal blood coagulation (clotting). The process of clotting is complex with a number of steps; a host of chemicals are involved. Calcium plays a part in a number of these steps.

Other roles

Calcium is a co-factor for many enzymes; this means that without the presence of calcium, these important enzymes cannot work as efficiently.

Calcium affects the smooth muscle that surrounds blood vessels, causing it to relax.

It is important to note that calcium is not easily absorbed without the presence of vitamin D.

Calcium-rich foods

According to health authorities in North America and Western Europe, dietary calcium can be found in several different foods and drinks; they also recommend that we obtain our calcium from a variety of sources.

The following foods and drinks are rich sources of calcium:

  • milk
  • cheese
  • yoghurt
  • seaweeds, such as kelp, hijiki, and wakame
  • nuts and seeds, including pistachio, sesame, almonds, and hazelnuts
  • beans
  • figs
  • broccoli
  • spinach
  • tofu
  • dandelion leaves
  • many fortified breakfast cereals

Also, many drinks, including soy milk and a variety of fruit juices are fortified with calcium.

Crushed eggshells contain calcium and can be ground into a powder and added to food and drink.

Some dark green vegetables may contain high levels of oxalic acid which reduces the body's ability to absorb calcium.

How much calcium should I consume each day?

According to the (IoM), we should consume calcium daily at the following amounts:

  • age 1-3 years: 700 milligrams (mg) per day
  • age 4-8 years: 1,000 mg per day
  • age 9-18 years: 1,300 mg per day
  • age 19-50 years: 1,000 mg per day
  • breast-feeding or pregnant teenager: 1,000 mg per day
  • breast-feeding or pregnant adult: 1,000 mg per day
  • age 51-70 years (male): 1,000 mg per day
  • age 51-70 years (female): 1,200 mg per day
  • age 71+ years: 1,200 mg per day

Calcium deficiency and calcium supplements

People with calcium deficiencies (hypocalcemia) are usually advised to take calcium supplements. The supplements should be taken with food for best absorption and to minimize possible undesirable side effects. Each intake of supplements should not exceed 600 milligrams; if more than that is consumed in one go, the excess will not be absorbed as well.

According to the NIH (National Institutes of Health), approximately of all American adults take dietary supplements, including 70 percent of adult females. Users increase their daily calcium intake by about an average of 300 milligrams per day through supplements.

Calcium supplements should be consumed at intervals spread throughout the day, usually two or three times a day. Vitamin D is added to many calcium supplements because it encourages the synthesis of proteins in the body, which make the absorption of calcium possible.

Choosing the right supplement these days can be confusing; there are various types in a wide range of combinations and preparations. Which one to select depends on the patient's needs and preferences, their medical condition, and whether they are on any medications.

Elemental calcium - the pure mineral - exists in its natural form with other compounds. Calcium supplements may contain different kinds of calcium compounds and varying amounts of elemental calcium, for example:

Calcium carbonate contains 40 percent elemental calcium. This type is more commonly available; it is relatively cheap and convenient. It is absorbed best when taken with food because it needs stomach acid to be absorbed.

Calcium lactate contains 13 percent elemental calcium.

Calcium gluconate contains 9 percent elemental calcium

Calcium citrate contains 21 percent elemental calcium. Calcium citrate can be taken with or without food. It is useful for patients with inflammatory bowel disease, achlorhydria, and some absorption disorders.

Side effects of calcium supplements

Some patients report gastrointestinal symptoms, such as bloating, constipation, gas, or a combination of all three. 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 sometimes helps reduce the occurrence or intensity of the side effects.

As well as adding vitamin D, calcium sometimes has magnesium added, too.

The following conditions, circumstances, or illnesses are known as possible causes of hypocalcemia (calcium deficiency):

  • 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.
  • Postmenopausal women - those who consume a lot of caffeine, soda, or alcohol have a greater risk of having low levels of calcium.
  • Celiac disease, inflammatory bowel disease, Crohn's disease, and some other digestive diseases.
  • Some surgical procedures, including the removal of the stomach.
  • Kidney failure.
  • Pancreatitis.
  • Vitamin D deficiency.
  • Phosphate deficiency.
  • Osteoporosis.
  • Osteopenia.

Some people who follow a vegan diet may experience calcium deficiency if they do not seek out plant-based calcium-rich or calcium-fortified foods.

Also, individuals who are lactose intolerant may not get enough calcium if they do not carefully seek out non-dairy foods that are rich in calcium or have the mineral added to those foods.