Nutrition Basics

Calcium-Everything you need to know

5 Mins read

What is calcium?

Calcium is among one of the seven major minerals, it is the most abundant mineral found in the human body. About 99% of the calcium is located in hard structures such as bones ands teeth where it provides hardness to their structure, the remaining 1% of the calcium is found in muscle cells, nerve cells, blood, extracellular and intracellular fluids where it plays other important roles which are discussed further in this article. The hardening effect on bones and teeth is provided by ‘calcium hydroxyapatite‘ which is the primary crystalline form of calcium in bones and teeth. This is the part of bones that is depleted during diseases involving bone demineralization such as osteoporosis and osteomalacia.

How calcium levels in the body are regulated?

Calcium levels in the blood ranges from 8.8 to 10.8 milligrams per 100 milliliters. These levels are tightly regulated by several hormonal factors and are independent of dietary intake. The Parathyroid hormone(PTH), Calcitonin and Vitamin-D are responsible for the regulation of blood calcium levels.

The parathyroid gland senses the low blood calcium levels and releases Parathyroid hormone which performs 3 functions to bring back blood calcium levels to normal. It increases the intestinal calcium absorption by stimulating Vitamin-D dependent mechanism, It Mobilize calcium by stimulating osteoclasts cells in the bones and it decreases calcium excretion and increases its reabsorption by kidneys.

Thyroid gland on the other hand senses the increased calcium levels in the blood and secrete calcitonin which draws excess calcium from the blood by increasing it’s deposition into bones and inhibiting osteoclasts activity. Osteoclasts are cells that are responsible for the remolding of the bones. They act by removing old cells so that new cells can be developed.

Any kind of disruption in these mechanisms causes blood calcium levels to increase or decrease out of their optimal range which results in two medical conditions namely ‘Hypercalcemia‘, the rise of blood calcium levels above the normal range and ‘Hypocalcemia‘, the fall of blood calcium below the normal range. Hypercalcemia is recognized by symptoms such as gastrointestinal disturbances such as nausea, pain, constipation etc, Hypercalcemia also leads to bone related problems such as osteoporosis, osteomalacia and even arthritis, kidney stones, fatigue, lethargy, depression, memory loss and muscular failure. Hypocalcemia on the other hand is recognized by symptoms such as twitching in hands, face or feet, numbness, depression, memory loss, scaly skin, rough hair texture, change in nails, cramps, seizures and abnormal heartbeats.

Why calcium is essential?

Contrary to popular belief calcium plays many vital roles in human body besides providing strength to bones and teeth.

  • Strength of bones and teeth: As stated previously, 99% of total body calcium is stored in bones and teeth as a part of mineral complexes providing hardness to their structure. Hence, It is the most recognized role of calcium. It is also associated with proteins in bones, teeth and cartilage.
  • Muscle and nerve function: Calcium is crucial in functioning of excitable cells like Muscle fibers and nerve cells. In skeletal muscles it is vital for muscle contraction hence, calcium is beneficial for weight training or exercise which involves rapid muscle contraction. In neurons(nerve cells) calcium ions function to propagate nerve impulses. Insufficient calcium leads to poor nerve function, neuromuscular disability, seizures and memory loss.
  • Muscle contraction in the heart: Besides Skeletal muscle contraction calcium initiates electrical signal or action potential which is responsible for cardiac muscle contraction(muscles of heart).
  • Regulation of blood pressure: Calcium helps to regulate blood pressure because it is responsible for tightening and relaxation of the blood vessels when needed.
  • Blood clotting: It is pivotal for blood clotting during an injury. Calcium ions convert blood clotting factors VII, IX & X to their active form as well as conversion of prothrombin to thrombin which is the main enzyme in blood clotting.
  • Insulin production: Calcium ions are vital for proper insulin production by beta cells in pancreas. Insulin is a hormone which is critical for controlling blood sugar levels. Any disturbance in mechanism of insulin can lead to disease such as type 2 diabetes.
  • Acid base balance: Calcium is vital for maintenance of acid-base(pH) balance of the body.
  • Reproductive health: It is also involved in sperm motility and female reproductive cycle.

Food Sources of Calcium

When it comes to food sources milk and milk products tend to contribute the greatest in our diet. For example: A glass of milk(250ml) provides 300 milligrams of calcium. Beyond dairy products good sources of calcium are sardines, oysters, calms, tofu, almonds and dark green leafy vegetables such as kale, broccoli, collards, spinach also contains respectable amount of calcium. 

How much calcium do you need?

The Recommended Dietary Intake for calcium is 1300 milligrams per day for adolescents aged 11-18 years, 1000 milligrams per day for adult male and 1200 milligrams per day for adult female, Pregnant and lactating women require 1300 milligrams of calcium per day.

Calcium deficiency 

Calcium deficiency causes numerous disease conditions especially those related to bones.

Symptoms of calcium deficiency

  • Muscle cramps, aches and spasms
  • Numbness and tingling sensation in the arms, legs and feet
  • Extreme fatigue
  • Dry skin
  • Dry, broken and fragile nails
  • Brittle hair and hair loss
  • Acne
  • Severe deficiency also leads to psoriasis
  • Premenstrual syndrome
  • Dental problems such as tooth decay, cavities, brittle teeth


Osteomalacia is demineralization of bones due to a loss of calcium and phosphorus crystals. This causes the bones to become soft.  Osteomalacia is a result of a diet that is chronically low in calcium or low vitamin D status of an individual can also result in this disease.


Osteoporosis, which mostly affects older women, is characterized by loss in total amount of bone. It is not only caused by lack of calcium in the diet but other reasons such as decreased estrogen, lack of exercise etc. The bones affected in osteoporosis are more likely to be central bones, like the hip and spine.

Bowing of legs

During growing years calcium deficiency can result into poor bone mineralization. Bones become soft and pliable which can result in bowing of legs.

What causes calcium deficiency?

Low levels of vitamin D

Vitamin D is one of the main driver of calcium in the body and inadequate levels of vitamin D results in low levels of calcium.

Milk allergies

Milk and dairy products are one of the best sources of calcium but if you are lactose intolerant and have milk allergies you will not be able to obtain enough calcium through diet. You may say that I take my calcium from green leafy vegetables such as spinach but they are not reliable source of calcium, read further and you will get to know why.

Eating raw vegetables and whole grains

Raw vegetables especially the green leafy veggies contain oxalates and fiber that bind to calcium and prevent its absorption in the intestines. For instance, green leafy vegetables are considered good source of calcium but presence of oxalates, phytates and fibers in these foods decreases the calcium absorption significantly, as little as 5% of calcium from spinach is actually absorbed. Besides fibrous foods phytates are also found in whole grains, nuts, seeds and legumes. Phytates can also lead to other mineral deficiencies such as zinc, magnesium and iron.

Excess caffeine

If you drink too much coffee (4-6 cups a day) and energy drinks without eating enough calcium through diet that can cause low levels of calcium in the body because caffeine depletes calcium.

Low stomach acid

If you have stomach problems such as indigestion, bloating or acid reflux you probably have a weak stomach acid. A weak stomach acid hampers your ability to digest calcium properly.

What is the best form of calcium supplement?

Calcium supplements comes in many forms. Calcium carbonate, calcium acetate, and calcium citrate, as well as calcium gluconates, phosphates, lactates, and oyster shells, are the most common forms of calcium supplements. The best form is calcium carbonate supplements since, 36-42% of calcium from calcium carbonate supplements is absorbed which is the greatest amount compared to any other supplement, about 24-36% from calcium citrate, acetate, lactate and calcium gluconate is absorbed so they are the second best.


Calcium is the most abundant mineral in the human body and it is very crucial for survival on a second to second basis. As stated previously, besides providing structural integrity to bones calcium has a lot of other functions in the body such as nerve conduction, muscle contractions etc. Calcium from Dairy and animal based foods such as sardines, oysters, calms etc. is much more bioavailable than calcium from plant based foods such as green leafy vegetables. It is important to choose the right source of calcium in order to maximize its absorption and utilization by the body.






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About author
Hey, I am Chetan and i am the author of “The Primitive diets” I hold a degree in Nutrition sciences and create content around health and nutrition. My principles are centered around primitive and holistic values which have been used since hundreds and thousands of years to treat diseases and improve health.
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