Calcium is critical to immune function, and is essential for muscle contraction, nerve conduction, heart function, the coagulation of blood, and the body's production of energy. Calcium also reduces the chances of kidney stone development.

Although the American diet is usually thought of as being high in calcium, according to the National Institutes of Health, many Americans consume less than half the amount of calcium recommended to build and maintain healthy bones.

Symptoms of calcium deficiency include: muscle spasm or cramping, typically in hands or feet; hair loss., dry skin and nails which may also become misshapen, nausea and vomiting, headaches, abnormal heartbeats, yeast infections (candidiasis), anxiety and dementia, convulsions/seizures, and poor tooth and bone development.

High intakes of protein and caffeine both deplete calcium levels. Excessive intake of sodium, phosphates (from carbonated beverages) and alcohol, as well as the use of antacids containing aluminum also contribute to calcium depletion.

Vitamin D helps aid in calcium absorption.

PWHIV: Calcium absorption naturally declines as we age; the intestinal absorption problems of people living with HIV and several other conditions might compund this problem and put them at a higher risk of calcium deficiency.

Many people with HIV are on dairy-free diets because of lactose intolerance. This lack of dairy intake might further predispose some people to calcium deficiency.

Since magnesium is also commonly deficient in a significant percentage of people with HIV, calcium status may also be at risk: if magnesium becomes depleted in the body, calcium deficiency can follow.

Foods that are fortified with calcium, such as juices, soy and rice milk, tofu, and cereals are also good sources.

If you are currently taking any of the following kinds of medications, consult with your doctor before supplementing with calcium, as there may be potentially serious interactions (the list may look disturbingly long - but is actually a testament to the amount of research that has been done): alendronate (used to treat osteoporosis), antacids containing aluminum, blood pressure medications, corticosteroids, cholesterol-lowering medications, diuretics, digoxin, estrogen, gentamicin, metformin, quinolone antibiotics, seizure medications, tetracycline medications.

Available through the NIH Office of Dietary Supplements is a calcium fact sheet.

Also, Brigham Women's/Faulkner Hospitals' website has a thoroughly-researched entry on calcium.

A good overview of calcium's therapeutic uses can be found on University of Maryland's Center for Integrative Medicine's website.