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Introducing
Calcium - The Most Important Mineral of All!
Calcium is the most abundant mineral
in the human body. Over 99% of the body's calcium is found
in bones and teeth which consists mainly of hydroxyapatite
crystals (about 40% calcium and 60% phosphorus). The remainder
is found in blood, bodily fluids, muscle, and other tissues
where it plays a role in blood vessel contraction and dilation,
muscle contraction, nerve transmission, and glandular secretion.
Calcium is probably most recognized for it's important role
in maintaining bone health. The skeleton not only provides
structural support for muscles, it protects vital organs
and serves as a storage site for calcium.
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Why
Calcium?
Calcium and Osteoporosis
First of all, Calcium is a major structural
element in bones and teeth. The mineral component of bone
consists about 40% calcium and 60% phosphorus. Bone is a
dynamic tissue that is constantly remodeled throughout life.
The process involves resorption (old bones is removed) and
formation (new bone is formed). Bone cells called osteoclasts
begin the process of remodeling by dissolving or resorbing
bone. Bone-forming cells called osteoblasts then synthesize
new bone to replace the bone that was resorbed. During normal
growth, bone formation exceeds bone resorption. Osteoporosis
may result when bone resorption exceeds formation. Osteoporosis
is a debilitating disease affecting more than 25 million
Americans where 80% of them are women. Osteoporosis is caused
by low bone mass and the structural deterioration of bone
tissue, leading to bone fragility and an increased susceptibility
to fractures of the hip, spine, and wrist. There are several
reasons cause Osteoporosis, the most popular one is deficiency
in calcium. When the level of calcium in our bones drops
below a certain limit, Osteoporosis may occur. In addition
to calcium, magnesium and vitamin D are also needed to prevent
osteoporosis.
Calcium and Body Movements
Secondly, Calcium plays a role in mediating
the constriction and relaxation of blood vessels, nerve
impulse transmission, muscle contraction, and the secretion
of hormones, such as insulin. Excitable cells, such as skeletal
muscle and nerve cells, contain voltage-dependent calcium
channels in their cell membranes that allow for rapid changes
in calcium concentrations. For example, when a muscle fiber
receives a nerve impulse that stimulates it to contract,
calcium channels in the cell membraneto allow a few
calcium ions into the muscle cell. These calcium ions bind
to activator proteins within the cell that release a flood
of calcium ions from storage vesicles inside the cell. The
binding of calcium to the protein, troponin-c, initiates
a series of steps that lead to muscle contraction. The binding
of calcium to the protein, calmodulin, activates enzymes
that breakdown muscle glycogen to provide energy for muscle
contraction.
Calcium for Enzymes and Proteins
Calcium is necessary to stabilize or
allow for optimal activity of a number of proteins and enzymes.
The binding of calcium ions is required for the activation
of the seven "vitamin K-dependent" clotting factors
in the coagulation cascade. The term, "coagulation
cascade," refers to a series of events, each dependent
on the other that stops bleeding through clot formation
(see Vitamin K).
Regulation of Calcium Levels
Calcium concentrations in the blood and
fluid that surrounds cells are tightly controlled in order
to preserve normal physiological functioning. When blood
calcium decreases (e.g., in the case of inadequate calcium
intake), calcium-sensing proteins in the parathyroid glands
send signals resulting in the secretion of parathyroid hormone
(PTH). PTH stimulates the conversion of vitamin D to its
active form, calcitriol, in the kidneys. Calcitriol increases
the absorption of calcium from the small intestine. Together
with PTH, calcitriol stimulates the release of calcium from
bone by activating osteoclasts (bone resorbing cells), and
decreases the urinary excretion of calcium by increasing
its reabsorption in the kidneys. When blood calcium rises
to normal levels, the parathyroid glands stop secreting
PTH and the kidneys begin to excrete any excess calcium
in the urine. Although this complex system allows for rapid
and tight control of blood calcium levels, it does so at
the expense of the skeleton. See diagram.
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Calcium
in Food
Calcium is found in a variety of foods,
in particular, dairy products contain rich calcium. The
following is a list of the natural sources for rich calcium:
Brazil Nuts, Milk, Cheese, Caviar, Kelp, Pudding, Canned
Salmon, Canned Sardines, Turnip Greens and Yogurt
Note that not all calcium sources are alike. Calcium may
be poorly absorbed from foods high in oxalic acid such as
spinach, sweet potatoes, beans or rhubarb and phytic acid
such as unleavened bread, nuts, raw beans, grains and soy
isolates.
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