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]."
