There can be no doubt that calcium is an important bone mineral. Generations of doctors, grandmothers and mothers have taught us that we should drink lots of milk and take calcium supplements in order to maintain strong bones and teeth.

Calcium is also important to support other critical bodily functions such as controlling your blood pressure, maintaining your heart beat, stimulation of hormone secretions and clotting of blood. 

Calcium is lost daily in the urine, sweat and faeces. It should therefore be replaced in adequate amounts to maintain a positive calcium balance. Ninety nine percent of calcium is stored in bones and teeth and if calcium intake is insufficient it gets taken out of these stores. 

Strong evidence exists that a calcium intake of below 500 mg per day leads to accelerated bone loss which can cause osteoporosis and subsequent fractures.

Recommended Daily Intake 

Although the recommended daily allowance (RDA) varies from country to country, the diets of most individuals in western countries, including South Africa (500-600mg/d), most likely contain insufficient calcium.

The National Osteoporosis Foundation of South Africa (NOFSA) recommends the following:

How do I choose a calcium supplement?

Most individuals can easily get at least half of the calcium they need from food. If you are unable to modify your diet to get enough calcium on a daily basis, you obviously need to take a supplement.

 The important thing to remember when choosing a calcium supplement is to know what the elemental (true/ bio-available) calcium content of the supplement is. Calcium is never found free in nature, because it forms compounds, otherwise known as calcium salts. 

Several different calcium compounds are used in supplements, including calcium carbonate, calcium gluconate, calcium phosphate and calcium citrate. These compounds contain different amounts of elemental calcium and it is therefore important to know exactly what the elemental calcium content of your chosen product is, how many tablets to take and when you should take them.

Calcium supplements are available without prescription in a wide range of preparations and strengths and selecting one can be a confusing experience. Many people ask which calcium supplement they should take - the " best " supplement is the one that meets an individual's needs based on tolerance, convenience, cost and availability.

The following table will help you determine how much elemental calcium is present in the product you are taking:

Therefore, if 500 mg of calcium is required, you need to take 1250 mg of a calcium carbonate product (40% of 1250=500), 2000 mg of a calcium citrate preparation (24% of 2000 =500), etc.

Choose calcium products that are known brand names. Most brand name products are absorbed easily in the body. You can actually test your product by putting it in some vinegar. If it has not dissolved after 30 minutes, it will probably not dissolve in the stomach. Chewable and liquid calcium supplements dissolve well, because they are already broken down when they reach the stomach.

How do I take my calcium supplement?

Calcium, whether consumed from diet or supplements, is best absorbed when taken several times a day in amounts of 500 mg or less. It should be taken at least twice a day. When starting your supplementation, increase the dosage gradually i.e. start with 500 mg per day for the first week and add calcium slowly.

It is also important to read the product labels and follow the directions for use.

Calcium carbonate preparations are generally the cheapest and most widely used supplements. Calcium carbonate is also the most concentrated form of calcium, allowing for smaller quantities to be used. It is also best absorbed in the presence of stomach acid so it is important that calcium carbonate supplements be taken with meals.

Calcium citrate is better absorbed than calcium carbonate products, but it is more expensive and you need to take more of the supplement because the elemental calcium content is half that of calcium carbonate. 

Calcium citrate can however be taken throughout the day as it does not need the acid environment of the stomach to be absorbed and it should be considered as a supplement in the ageing patient who has impaired gastric function. If you are using acid blockers for indigestion, reflux or heartburn, it may also be better to use a calcium citrate. 

Special considerations when taking calcium supplementation:

• If you need to take an iron supplement as well, take your calcium supplement either two hours before or after the iron supplement to ensure proper absorption of both
• Calcium may interfere with the body's ability to use certain antibiotics like tetracycline − use calcium two hours before or after taking the tetracycline
• If you are using a bisphosphonate drug like Fosamax or Actonel for osteoporosis, do not take the calcium supplement in the morning, as it will interfere with the absorption of the medication 
• Excessive intake of protein, salt and caffeine may lead to an increased excretion of calcium in the urine 
• Calcium absorption is inhibited to a certain degree by fibre in the diet – try taking your calcium when you are having a low-fibre meal
• Although the calcium content in green vegetables like spinach is high, little gets absorbed due to the phytate content of these foods 
• Vitamin D is necessary for calcium absorption and is consumed in the diet and produced in the skin by the UV rays in sunlight. The RDA for vitamin D is 400 IU per day in persons under 70 and 800 IU in persons over 70 years of age. Pharmacological doses of vitamin D supplementation should be done under medical supervision. The aged and home-bound persons who are not exposed to sunlight should be supplemented with vitamin D 
• Special care should be taken when considering supplements that contain oyster shells, dolomite or bone meal as these may contain high doses of lead which can in the long run be harmful
  

Calcium and magnesium
Much has been written about this subject and while it is true that magnesium is important in calcium metabolism (low magnesium levels stimulate calcium excretion in the urine), it is generally accepted that most healthy individuals do not need additional supplementation for vitamins and minerals like magnesium, boron, vitamin K, vitamin C, sink, selenium etc. In fact, many of these nutrients will be present in a diet with five or more servings of fruit and vegetables a day.

Certain individuals may however be at risk for a magnesium deficiency including those with gastrointestinal diseases that cause poor absorption or increased losses of magnesium, frail elderly individuals eating poor diets, alcoholics, diabetics, individuals receiving chemotherapy and those taking high dose diuretics that deplete magnesium. Magnesium deficiency is easy to detect by doing a simple blood test. Your medical professional will prescribe a magnesium supplement if it is necessary or if you have a disease or condition that causes magnesium deficiency.

Side effects

• Calcium supplements in reasonable doses (1000 mg /day) are generally a satisfactory option for many people. Certain preparations may however cause patients to feel bloated and have constipation. If simple measures such as an increased fluid and fibre intake as well as exercise do not solve the problem, another form of calcium should be tried.
• Gastritis may be caused if calcium carbonate is taken between meals - this can stimulate rebound acid production in the stomach.
• There is no scientific evidence that calcium causes kidney stones. If you do have kidney stones and have hypercalcuria (determined by a 24 H urinary), it is probably wise to limit your intake to about 1000 mg. If you have normal urinary calcium levels in the presence of kidney stones, it is not necessary to limit your calcium intake, but care should be taken with vitamin D supplementation and should be done after consultation with a doctor. 

A total daily intake of more than 2500 mg of calcium is not recommended- it is not more beneficial for the bones and the kidney just needs to work harder to eliminate the excess calcium.

Summary

Whereas calcium is an essential mineral required to build bone mass and to slow age-related bone loss, calcium alone will not protect against bone loss as a result of oestrogen deficiency in the post-menopausal female. It will also not provide protection against bone loss resulting from physical inactivity, too much alcohol, smoking or using bone toxic drugs like cortisone. An adequate calcium intake is therefore only one of many measures to ensure a healthy skeleton.

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(Thereza Hough, National Osteoporosis Foundation of South Africa)

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