Calcium: The Most Abundant Mineral By Kevin Connolly, Ph.D
Introduction
Calcium (Ca), an essential metallic element in human
nutrition, fulfils a wide variety of biological roles. You are
probably quite familiar with its celebrated structural role as a
primary mineral component of bones and teeth, but did you
know calcium also directly participates in a myriad of metabolic
reactions, including those that control energy production,
muscle contraction, heartbeat, blood coagulation, and the
functions of the immune, nervous, and endocrine systems? The
human body derives its entire pool of calcium from the diet,
and not surprisingly, has evolved an intricate system for the
absorption, distribution, storage, and maintenance of relevant
calcium levels. So is it necessary to take a calcium supplement
to support all these functions? For most people, absolutely!
Sources and Forms of Calcium
~Food~
We can consume calcium as naturally-occurring components
of dietary foodstuffs (dairy products, dark green vegetables,
and to a lesser extent meats, fish, and legumes). Sadly, the
average American adult is estimated to intake between 500 to
800 mg of calcium per day, with men having higher average
intakes than women. This average intake is significantly less
than the established Dietary Reference Intake (DRI) of 1,000
mg/day for adults aged 19 to 50, and 1,200 mg/day for those
over 50. The disparity is likely attributed to the evolving (or
devolving) Western diet (in which many high-calcium foods
like broccoli, mustard greens, and sardines have fallen out of
favor) and our avoidance or intolerance of dairy products as we
age. Compounding factors such as poor vitamin D status and
carbonated soft-drink consumption have been shown to further
decrease the amount of usable calcium in the body. Studies have
shown that poor calcium status, especially early in life, can have
lasting, irreversible, detrimental effects as we age.
~Supplements~
Increasingly, supplementation has been required. Currently,
an estimated 25% of U.S. women take a calcium supplement.
These supplements are available in a variety of different
forms, usually as calcium salts (gluconate, citrate, carbonate,
phosphate, among others). There has been considerable debate
as to the merits of each (particularly in bioavailability), but it is
important to note that nearly all have been demonstrated to
serve as good calcium sources under most conditions, and any
differences between them are usually modest. This is due to
the complex, highly regulated system that the human uses to
absorb and utilize calcium.
Calcium Absorption
Calcium is absorbed in the small intestine (and possibly
the large intestine) both actively (by a transport system) and
passively (by diffusion). The combination of active and passive
absorption allows the digestive system to rapidly respond
to the body's calcium requirements; ensuring calcium is
efficiently absorbed when dietary intake is low, but preventing
over-absorption (and undue stress on the renal system) when
dietary calcium levels are high. Calcium absorption is limited
to approximately 1/4 to 1/3 of ingested calcium, assuming
dietary calcium levels are also adequate. These values are
also altered during different points in human development,
increasing significantly during periods of rapid growth (during
infancy, puberty, pregnancy) and declining later in life (after
menopause, intestinal calcium absorption decreases by about
0.2% annually)
In general, calcium is absorbed in its free (elemental) form.
This means it must be released (dissociated) from its bound
salt or protein in order to be absorbed. In healthy individuals
with sufficient calcium intake, the rates of dissociation
of different calcium salts are similar; hence, differences in
bioavailability of different forms of calcium are modest under
these circumstances.
Calcium in bones and other Systems
The skeleton is the reservoir for calcium, where it
performs a structural role in the bone composite, but can
also be released into the blood for use in other body systems.
Bone calcium is in the form of hydroxyapatite (scientifically
known as Ca10(PO4)6(OH)2,) a calcium phosphate mineral.
If more calcium is released from bone than is replaced
(which may occur if dietary calcium levels are insufficient,
or as a consequence of imbalanced hormone levels following
menopause), a net loss of bone calcium can occur, which can
decrease the bone's density and increase the risk of fracture.
Mineral in Your body
Limitations
Calcium is of obvious importance in human health, but one must
also consider its interdependency with other nutrients when choosing
to improve calcium status. Calcium intake at a level relevant to one's
age group is important, but equally as important is ensuring proper
amounts of vitamin D (though diet, supplementation, or sunlight
exposure) to mobilize the dietary calcium from the intestines to
the systems where it
is needed. Calcium,
although required, is not
sufficient for the growth
of bone or the maintenance
of bone mineral
density. This is consistent
with our knowledge of
the complex chemistry
of bone formation, and has been demonstrated in controlled clinical
settings. The incorporation of calcium into bones depends on some
controllable dietary and lifestyle factors, particularly sufficient trace
minerals (like iron, silicon, boron, copper), vitamins (notably vitamin
K), as well as factors which build a strong bone matrix (such as
physical activity).
Bone-Up, from Jarrow, combines microcrystalline hydroxyapatite
(MCHA), from free-range Australian calves, with essential vitamins
and minerals for optimal calcium absorption and increased bone
density and hardness. Vitamin K2, as MK-7 (a more bioavailable form
of vitamin K) and 1000 IU of vitamin D3 help support the deposition
of calcium into the bones as well as assist in building the organic bone
matrix. Minerals such as magnesium, zinc, manganese, and boron are
essential for optimal bone health. Also added is the nutrient potassium
citrate, for optimal osteo support.