Calcium is the most abundant mineral in our body, it constitutes about 1.5-2.0 percent of our body weight. Found mostly in bones and teeth and some in other tissues and the circulation.

Many other nutrients, vitamin D, and certain hormones are important to calcium absorption, function, and metabolism. Phosphorus as well as calcium is needed for normal bones, as are magnesium, silicon, strontium, boron, and the protein matrix - all part of our bone structure. The ratio of calcium to phosphorus in our bones is about 2.5:1.

Calcium works with magnesium in its functions in the blood, nerves, muscles, and tissues, particularly in regulating heart and muscle contraction and nerve conduction. Maintaining a balanced blood calcium level is essential to life, especially for cardiac function. A normal blood calcium level is about 10 mg per 100ml of blood.

The most important factor in taking any nutrient is its absorption by the body. Vitamin D is essential in absorption of calcium. However many doctors do not consider this important absorption issue and prescribe an oyster shell or dolomite or bonemeal source as a calcium supplement. Frequently, calcium lactate or calcium carbonate (such as Tums) pills - which are more alkaline and slowly absorbed- are prescribed without suggesting additional vitamin D and magnesium, so important for calcium balance and metabolism. A woman who needs more calcium could be taking an extra gram a day without really getting much of it into her blood or bones. Besides vitamin D, vitamin A and C can help support normal membrane transport of calcium. Some protein and fat help absorption of calcium but in excess may actually interfere.

Lactose helps calcium absorption, and because of this as well as the protein-fat combination, the calcium content of milk is a reliable source of easily assimilated calcium. For other reasons, though, milk is not an ideal food for many people, especially the homogenized variety fortified with synthetic vitamin D, making milk a less-than-perfect (and definitely not the only) source of calcium. Nonfat milk does not improve calcium absorption and in fact, may decrease it.

Gastric hydrochloric acid (stomach acid) helps calcium absorption. The duodenum is the main location for absorption of calcium because farther down the small intestine the local environment becomes too alkaline. A fast-moving intestinal tract can also reduce calcium absorption.

Exercise has been shown to improve absorption, and lack of exercise can lessen it. Stress also can diminish calcium absorption, possibly through its effect on stomach acid levels, digestion, and intestinal motility.

Many dietary factors also reduce calcium absorption. Foods that are high in oxalic acid, such as spinach, rhubarb, chard, and chocolate, can interfere with calcium absorption by forming insoluble salts in the gut.

Because of many complex factors affecting calcium absorption, anywhere from 30-80% may end up being excreted. The kidneys also control calcium blood levels through their filtering and reabsorption functions. Excess salt intake can lead to increased calcium losses in the urine. Sugar intake may reduce the reabsorption of calcium and magnesium and cause more to be eliminated.

When the diet is high in phosphorus, we can lose extra calcium through the urine, resulting in calcium being pulled out of the bones. Phosphorus is plentiful in meat foods and is of particular concern in soda pops that have added phosphoric acid (phosphate). This phosphorus-calcium imbalance may lead to kidney stones and other calcification problems, as well as increased atherosclerotic plaque.

Overall, we need good sources of calcium in our diets, good nutritional habits, and a diet that promotes healthy gastrointestinal function. Taking calcium and magnesium at bedtime or between meals, when the stomach may be more acidic, is often helpful for better absorption.

Functions of Calcium in the body:

Development and maintenance of bones and teeth. The calcium in bones is being added to and removed depending on the calcium balance in the body. The bones provide calcium to the blood and other tissues when we are not getting sufficient amounts from our diet. Vitamin D, Parathyroid hormone and calcitonin are responsible for maintaining this balance.

Circulating calcium plays many vital functions. Ionized (Ca++) is needed for muscle contractions as in muscular activity and in regulating the heartbeat. Heart function is mediated by several minerals: calcium stimulated contraction, magnesium supports the relaxation phase, and sodium and potassium are also important in generating the electrical impulse. Exercise can improve the circulation of calcium as well as that of all the other nutrients and thereby help the tone and function of the muscles, heart, and nervous system.

With regards to nervous system, calcium is important in nerve transmission. Calcium ions influence nerve and cell membranes and the release of neurotransmitters such as acetylcholine. Calcium is calming to the nerves. Mild calcium deficiency can cause nerve sensitivity, paresthesias, muscle twitching, brittle nails, irritability, palpitations, insomnia, confusion, or a feeling of chronic depression.

Is milk the best source of calcium?

The recommended Daily Allowance for calcium for growing children is: 500mg for infants up to one year, 800mg for children up to age 10; 1000mg for children up to 18 years as well as adults, and 1200gm for pregnant, lactating and postmenopausal women. However these figures were derived from experiments utilizing diets high in phosphorus. Phosphorus binds to calcium in the intestine, preventing its absorption. It also leaches calcium from the body. The ratio of calcium to phosphorus in cow's milk is 1.2: 1.0.

If your diet is low in phosphorus, you should take only about one-tenth the recommended amount of calcium or 100mg.

Breast milk contains 300mg of calcium per quart and cow's milk has 1200mg of calcium per quart, yet infants absorb more calcium from breast milk. The calcium to phosphorus ratio in breast milk is 2:1, which emphasizes the importance of this ratio for proper calcium absorption. Milk and dairy products, poultry, some fish, whole wheat, cereal products, peas, sunflower seeds, meats, and dark green leafy vegetables have a low calcium to phosphorus content, which interferes with adequate absorption and use of calcium. Meat also has a high phosphorus content.

Acid forming diets increase calcium excretion. Meats, other high-protein foods, and most cereal grains, including wheat, are acid forming; most vegetables and fruits do not have this effect.

Nutrients necessary for the proper absorption and utilization of calcium include magnesium, manganese, potassium, zinc, and vitamin D.

Sources of Calcium for 100g edible portion or 3 ½ ounces:

Calcium Supplements

When purchasing calcium supplements, ensure to look for the elemental calcium content, not the total content. For instance, a pill containing 500mg of Calcium Carbonate provides 200mg of elemental calcium. Hence one pill in this example only provides 200mg of calcium, not 500mg.

Different Types of Calcium Supplements

• One important factor affecting calcium absorption is how well the pill dissolves.
• Calcium Carbonate e.g. Tums or Caltrate: Most calcium pills in the market are in the form of calcium carbonate. It requires extra stomach acid for better absorption, hence it is best taken after meals.
• Calcium Citrate e.g. Citracal or Solgar: Calcium is best absorbed in an acidic environment, hence calcium citrate is the best absorbed supplemental form of calcium. It does not require extra stomach acid for absorption, hence we may take it anytime in a day, even on an empty stomach. However Calcium Citrate usually provides less elemental calcium per pill, therefore one may need to take a relatively more numbers of pills per day depending to the needs. Cautions for people with acid reflux. Also citrate has been shown to increase the absorption of aluminum by the body.
• Dolomite, Bone Meal or Oyster Shell: These naturally occurring calcium pills may contain heavy metal or lead. At the moment, calcium supplements are not tested by any regulatory agency for lead content. Therefore, it's best to avoid.
• Calcium Gluconate and Calcium Lactate: These types of calcium pills contain low content of elemental calcium. Hence, one may need to take a large amount of tablets to meet the calcium requirement!
• Coral Calcium: This type of calcium is marketed for more than bone health. Its infomercial claimed that it can cure 200 human diseases. It's indeed only Calcium Carbonate.

Advisory:

Patients who are taking Levothyroxine for treatment of hypothyroidism should take calcium supplements at least 4hrs apart from their medication. ([Home Health Nurse] 2004 May; 22 (5), pp. 338-9. Author: Neafsey, PJ)

Possible Interactions with: Calcium

Alendronate

Calcium may interfere with the absorption of alendronate, a medication used to treat osteoporosis. Calcium containing products, therefore, should be taken at least two hours before or after alendronate.

Antacids, Aluminum-containing

When calcium citrate is taken with aluminum containing antacids, the amount of aluminum absorbed into the blood stream may be increased significantly. This is a particular problem for people with kidney disease in whom the aluminum levels may become toxic. In addition, aluminum-containing antacids may increase the loss of calcium in the urine.

Blood Pressure Medications

Taking calcium with a beta-blocker (such as atenolol), a group of medications used for the treatment of high blood pressure or heart disorders, may interfere with blood levels of both the calcium and the beta-blocker. Study results are conflicting, however. Until more is known, individuals taking atenolol, or another beta blocker, should have their blood pressure checked before and after adding calcium supplements or calcium containing antacids to their medication regimen.

Similarly, it has been reported that calcium may reverse the therapeutic effects as well as the side effects of calcium channel blockers (such as verapamil) often prescribed for the treatment of high blood pressure. These study results are also controversial. People taking verapamil or another calcium channel blocker along with calcium supplements should likely have their blood pressure checked regularly.

Cholesterol-lowering Medications

A class of medications known as bile acid sequestrants (including cholestyramine, colestipol, and colesevelam), used to treat high cholesterol, may interfere with normal calcium absorption and increase the loss of calcium in the urine. Supplementation, therefore, with calcium and vitamin D may be recommended by your healthcare provider.

Corticosteroids

Corticosteroid medications reduce the absorption of calcium, thereby increasing the risk for bone loss and osteoporosis over time. This is of particular concern for anyone who is maintained on long-term steroids.

Digoxin

High levels of calcium may increase the likelihood of a toxic reaction to digoxin, a medication used to treat irregular heart rhythms. On the other hand, low levels of calcium cause this medication to be ineffective. People who are taking digoxin should have calcium levels monitored in the blood closely.

Diuretics

Two different classes of diuretics interact with calcium in opposite ways-thiazide diuretics such as hydrochlorothiazide can raise calcium levels in the blood, while loop diuretics, such as furosemide and bumetanide, can decrease calcium levels. In addition, amiloride, a potassium-sparing diuretic, may decrease the amount of calcium excreted in the urine (and subsequently increase calcium levels in the blood), especially in people with kidney stones.

Estrogens

Estrogens may contribute to an overall increase in calcium blood levels. Taking calcium supplements together with estrogens improves gain in bone density significantly.

Gentamicin

Taking calcium during treatment with the antibiotic gentamicin may increase the potential for toxic effects on the kidneys.

Metformin

Metformin, a medication used to treat type 2 diabetes, can deplete levels of vitamin B12. Some early evidence suggests that calcium supplements may prevent or eliminate this negative effect of metformin. More research is needed.

Antibiotics, Quinolones

Calcium can interfere with the body's ability to absorb quinolone antibiotics (such as ciprofloxacin, levofloxacin, norfloxacin, and ofloxacin). If taking calcium containing supplements or antacids, therefore, you should take them two to four hours before or after taking quinolone antibiotics.

Seizure Medications

Low levels of calcium have been reported with high doses of seizure medications, such as phenytoin, which may decrease calcium absorption. Some physicians recommend vitamin D along with anti-seizure drugs to try to prevent the development of low calcium levels.

Tetracyclines

Calcium can interfere with the body's ability to absorb tetracycline medications (including doxycycline, minocycline, and tetracycline) and, therefore, diminish their effectiveness. Calcium containing supplements and antacids should be taken at least two hours before or after taking these drugs.

For more information on Calcium and drug interactions please visit the link: ajc.com