The National Institutes of Health Office of Dietary Supplements provided the following description in the Sep. 23, 2005 document "Dietary Supplement Fact Sheet: Calcium," published on the Office's website:
"Calcium, the most abundant mineral in the human body, has several important functions. More than 99% of total body calcium is stored in the bones and teeth where it functions to support their structure. The remaining 1% is found throughout the body in blood, muscle, and the fluid between cells. Calcium is needed for muscle contraction, blood vessel contraction and expansion, the secretion of hormones and enzymes, and sending messages through the nervous system. A constant level of calcium is maintained in the body fluid and tissues so that these vital body processes function efficiently."
The Harvard University School of Public Health (HSPH) reported in their Dec. 13, 2004 article "Calcium and Milk," published on the HSPH website Nutrition Source:
"Calcium is a mineral that the body needs for numerous functions, including building and maintaining bones and teeth, blood clotting, the transmission of nerve impulses, and the regulation of the heart's rhythm. Ninety-nine percent of the calcium in the human body is stored in bones and teeth. The remaining 1% is found in the blood and other tissues.
The body gets the calcium it needs in two ways. One is by eating foods that contain calcium. Good sources include dairy products, which have the highest concentration per serving of highly absorbable calcium, and dark leafy greens or dried beans, which have varying amounts of absorbable calcium.
The other way the body gets calcium is by pulling it from bones. This happens when blood levels of calcium drop too low, usually when it's been a while since having eaten a meal containing calcium. Ideally, the calcium that is 'borrowed' from the bones will be replaced at a later point. But, this doesn't always happen. Most important, this payback can't be accomplished simply by eating more calcium."
Jane Higdon, PhD, explained in her April 8, 2003 document "Micronutrient Information Center: Calcium," published on the website of the Linus Pauling Institute:
"Calcium is the most common mineral in the human body. About 99% of the calcium in the body is found in bones and teeth, while the other 1% is found in the blood and soft tissue. Calcium levels in the blood and fluid surrounding the cells (extracellular fluid) must be maintained within a very narrow concentration range for normal physiological functioning. The physiological functions of calcium are so vital to survival that the body will demineralize bone to maintain normal blood calcium levels when calcium intake is inadequate.
Thus, adequate dietary calcium is a critical factor in maintaining a healthy skeleton... Osteoporosis is a skeletal disorder in which bone strength is compromised, resulting in an increased risk of fracture... Calcium is the nutrient consistently found to be most important for attaining peak bone mass and preventing osteoporosis...
The relationship between calcium intake and blood pressure has been investigated extensively over the past two decades... This research indicates that a calcium intake at the recommended level (1,000-1,200 mg/day) may be helpful in preventing and treating moderate hypertension [high blood pressure]."