Calcium is one of the most important minerals for the growth, maintenance, and reproduction of the human body. Calcium is essential for the formation of and maintenance of healthy teeth and bones.

The bones incorporate calcium into their structure. Like other tissues in the body, bones are continually being reabsorbed and re-formed. Teeth incorporate calcium in their structure in a manner similar to bones.

Calcium has other functions in addition to maintaining healthy teeth and bones. Blood coagulation, transmission of nerve impulses, muscle contraction and relaxation, normal heartbeat, stimulation of hormone secretion, activation of enzyme reactions, as well as other functions all require small amounts of calcium.

Many foods contain calcium, but dairy products are the most significant source. Milk and dairy products such as yogurt, cheeses, and buttermilk contain an efficiently absorbed form of calcium.

For children between the ages of 1 and 2 years old, whole milk (4%) is recommended. The fat content of dairy products is a concern for adults and children over the age of two. You can easily reduce the fat content of dairy products while maintaining the calcium content by selecting low-fat (2% or 1%) or skim milk.

The calcium is not contained in the "fat portion" of milk, so removing the fat will not affect the calcium content. In fact, when you replace the fat portion that has been removed with an equal part of skimmed milk, you are actually increasing the calcium content. Therefore, one cup of skim or non-fat milk will have more calcium than one cup of whole milk because almost the entire cup of skim milk is the made up of the calcium-containing portion!

Other dairy products such as yogurt, most cheeses, and buttermilk are excellent sources of calcium and are available in low-fat or fat-free versions.

Milk is also a good source of phosphorus and magnesium, which help the body absorb and use the calcium more effectively. Vitamin D is essential for efficient utilization of calcium. Milk is fortified with vitamin D for this reason.

Green leafy vegetables such as broccoli, collards, kale, mustard greens, turnip greens, and bok choy or Chinese cabbage are good sources of calcium. Certain green vegetables are less effective sources of calcium. While their calcium content appears to be high, their fiber and oxalic acid content interferes with the absorption of calcium.

Other sources of calcium are salmon and sardines canned with their soft bones. Shellfish, almonds, Brazil nuts, and dried beans are also sources of calcium. It is difficult, however, to eat adequate quantities of these foods to achieve optimal calcium intake.

Several food products, such as breads and orange juice, are enriched with calcium to make them a significant source of calcium for people whose dairy product consumption is inadequate.

Increased calcium intake for limited periods does not normally cause toxic effects. The urine and the feces easily eliminate any excess calcium. However, an increased risk of kidney stones in persons susceptible to them has been associated with chronically high calcium intake.

Low intakes of calcium for prolonged periods of time can lead to calcium deficiency. This condition leads to osteoporosis, loss of the jaw bone (and secondary oral health problems), hypertension, and other disorders.

Persons with lactose intolerance have trouble digesting lactose, the sugar in milk. Lactose intolerance is due to an inability to produce lactase, the enzyme that digests milk sugar. The wall of the gastrointestinal tract normally produces this enzyme. In some people, due to diseases of the gastrointestinal tract or to hereditary factors, this enzyme cannot be produced by the body.

Fortunately, lactase can be synthetically produced and bought in various over-the-counter formulations, and taken orally with milk to aid in its digestion. You can also buy lactose-free milk at most grocery stores.

In rare instances, some people have a true allergy to the protein in milk. This condition requires restriction of all dairy products. These individuals may have trouble obtaining enough calcium in their diet and may need to take calcium supplements.

Calcium recommendations vary depending on age and special needs. In addition, levels of estrogen can affect calcium needs in women.

The U.S. Department of Agriculture has a PDF file that lists these recommendations.

Vitamin D is required for adequate amounts of calcium to be absorbed into the body, and for adequate calcium levels to be maintained. Therefore, when choosing calcium supplements, those that also contain the RDA of vitamin D are preferred.

Comparing the RDA to the food sources of calcium helps to put the RDA in perspective:

• 8-ounce glass of milk = 300 milligrams
• 2 ounces of Swiss cheese = 530 milligrams
• 6 ounces of yogurt = 300 milligrams
• 2 ounces of sardines with bones = 240 milligrams
• 6 ounces of cooked turnip greens = 220 milligrams
• 3 ounces of almonds = 210 milligrams

A total intake of up to 2,000 milligrams per day from dietary sources and supplements appears to be safe. The preferred source of calcium is calcium-rich foods such as dairy products.