An adult contains around one kilogram of calcium, which is the most abundant mineral in the human body. Bones and teeth store around 99% of our calcium and 1 per cent is used to support metabolic functions. Levels of calcium in the blood are tightly controlled, as the slightest deviations may result in serious symptoms of the nervous system and the heart.
Vitamin D is important for the uptake of calcium in the digestive system. Parathyroid hormone (PTH) that is produced in the parathyroid gland is able to increase blood levels of calcium by releasing calcium from the bones and reducing the secretion of calcium from the kidneys. That way our bone tissue functions as a depository and a source of calcium which serves to maintain a constant concentration of calcium in the blood, in muscle tissue, and in intracellular fluids.
Functions and imporatnce for
- Strong bones. Together with magnesium and phosphorous, calcium constitutes the solid matter of bone tissue
- Strong teeth
- Energy turnover
- Nerve impulse transmission
- Blood pressure
- Muscle function and muscle contraction
- Blood coagulation
- Digestive enzymes
- Cell division and cellular functions in the body
Deficiencies and poor utilisation may be caused by
- Lack of gastric juice
- Lack of vitamin D and magnesium
- Oxalic acid (found in e.g. acidic leaves, tea, spinach, cocoa, rhubarb)
- Phytin. Found in the shell components from grain. Soaking and prolonged rising may activate phytase that breaks down phytin.
- Insufficient strain on bones which contributes to reduced bone mass
- Muscle fatigue
- Muscle cramps
- Impaired growth
- Insidious decalcification of the skeleton
- Osteoporosis (typically manifests itself as bone fractures)
- Rickets (in combination with vitamin D deficiency)
- Bad teeth and dental decay
- Elevated blood pressure
- Colon cancer
- Also, see the following section
Too low calcium levels in the blood (hypocalcemia)
The body's ability to collect calcium from the reserves in bones is lower than normal. This condition occurs in situations with reduced
parathyroid gland function, bone diseases, and kidney diseases.
- Tingling (needles and pins sensation) in fingers - early symptom
In severe cases:
- Mental disturbances
- Cardiac arrest
Mainly dairy products, seaweed, stinging nettle, green vegetables such as kale, beans, parsley, and spinach. Also found in almonds, nuts, seeds, kernels, herbs, eggs, and bone broth. Water is also a source of calcium - especially "hard" water.
Calcium content in mg per 100 grams
(average value in Denmark)
Recommended daily allowance (RDA)
Adults: 11 years of age and older: 800 mg
Children: 1-10 years of age: 600 mg
Pregnancy and lactation: 900 mg
- The above mentioned deficiency symptoms
- Pregnancy and lactation
- Older people
- Post-menopausal women
- People at risk of osteoporosis
IMPORTANT: Often related to lack of vitamin D and magnesium.
Bone formation, bone resorption, and bone mineral density (BMD)
Bones are in a constant state of remodeling throughout life. In children and youngsters, the bone formation is greater than the bone resorption (breakdown of bone tissue). At midlife, the process shifts towards an equilibrium where bone mass is kept intact. In the late adult years, our bone tissue deteriorates to a greater extent that it gets restored, causing a net loss. A lot is determined by diet and exercise habits (especially the type of exercise that strains the bones). Bone mineral density is detected by measuring the amount of calcium and other minerals in bone tissue
Nutritional supplements - types of calcium
Calcium carbonate: 1000 mg provides 400 mg of calcium. Should ideally be taken with a meal. Some people tend to get constipated but this is preventable with supplements of magnesium. Calcium carbonate neutralises stomach acid and is also found in certain antacids.
Calcium citrate: 1000 mg provides 210 mg of calcium. Calcium citrate can be taken independently of meals.
Coral calcium: Consists of calcium carbonate and trace elements.
Calcium lactate and calcium gluconate: Contains less concentrated forms of calcium.
Calcium chelate: Synthetically manufactured compound where calcium is bound to organic molecules.
Overdosing - side effects
Mainly from large ingestion of dairy products and/or mono supplementation
- Inhibits the uptake of iron
It is estimated that it takes more than 2,500 mg of calcium daily before noteworthy adverse effects occur. Nonetheless, this depends on the relation between levels of vitamin D and magnesium.
Elevated calcium levels in the blood (hypercalcemia - calcium poisoning)
Usually caused by underlying disease such as an overactive parathyroid gland and cancer
Minor symptoms include:
- Fatigue and drowsiness
- Nausea and vomiting
- Excessive urination
- Deposition of calcium in kidneys and stones in the urinary tract
- Extreme fatigue, both physically and mentally. This condition, left untreated, may lead to cardiac failure
- Serious problems in the central nervous system
Important information about interactions, requirements, and supplements
Vitamin D and the balance between calcium and magnesium is highly important to ensure that the calcium, which is absorbed by the body is properly embedded in the bones and in other metabolic functions. Vitamin K2 also contributes to the maintenance of strong bones.
Children shall not consume more than 50 cl of milk or similar dairy products per day, as this may lead to malnutrition and inhibit the uptake of iron. People who do not consume dairy products are advised to take supplements of calcium (preferably in combination with magnesium and vitamin D).
The major part of the global population does not consume dairy products and covers the daily need for calcium by means of other foods.
Avoid taking calcium supplements in the case of hypercalcemia (too much calcium in the blood), impaired kidney function, or tendency towards kidney stones.
Calcium supplements may interfere with the effect of penicillin and drugs against Parkinson's disease. If in doubt, ask a physician.