Calcium is a substance that the body uses for many functions, particularly building strong bones and teeth. Calcium is also required for blood to clot properly when bleeding occurs. Normally, the body stores calcium in bones, but when there is insufficient calcium intake, and levels of calcium in the blood drop, calcium is drained from the bones to replenish blood levels. This can retard bone growth in children or cause brittle bones in adults (see osteoporosis). Other symptoms of severe calcium deficiency can include dental problems, excessive bleeding, heart problems and irritability.

Good sources of dietary calcium dairy products (milk, cheese, yogurt, ice cream), canned salmon and sardines, broccoli, tofu, almonds and figs, as well as calcium-fortified products such as calcium-fortified orange juice.

In order for the body to absorb and use calcium, other substances need to be present in the blood as well. Vitamin D is one substance which helps the body absorb calcium and deposit it in the bones. Without vitamin D, calcium may simply be passed out of the body in urine.

There are a great many calcium supplements available on the market today, and they vary widely in effectiveness and in how easily the particular form of calcium is absorbed into the body. If you do decide to take supplements, be sure you know what you're getting. When starting any dietary supplement, talk to your doctor to make sure that there is no conflict with other medication or medical conditions. Excess calcium in the body can cause serious medical problems including muscle weakness, constipation, nausea and cardiac arrest.