General Description
Calcium is the most abundant mineral in the human body, making up
1.5 to 2 percent of total body weight. Approximately 99 percent
of the body's calcium is located in the bones and teeth. Calcium
is essential for bone development and maintenance, and plays important
roles in much of the body's enzyme activity. It is required for
muscle contraction, blood clotting, transmission of nerve signals,
and regulation of heartbeat. Supplemental forms of calcium include
bone meal, dolomite, refined calcium carbonate, unrefined calcium
carbonate (derived from limestone or oyster shells), and calcium
chelates (such as aspartate, citrate, gluconate, or lactate).
Food sources
The best food sources of calcium include milk and dairy products,
kale, spinach, swiss chard, and members of the cabbage family.
Health applications
Deficiency symptoms
Calcium deficiency in children may lead to rickets, a condition
marked by bone deformities and retarded growth. In most cases, rickets
is not caused by a lack of dietary calcium but by a deficiency in
vitamin D, a nutrient required for calcium absorption. In adults,
calcium deficiency may cause osteomalacia or osteoporosis. Other
conditions associated with low calcium intake include muscle spasms
and cramps, and high blood pressure.
Calcium and bone strength
Most research on calcium has focused on its role in bone health,
specifically the prevention of osteoporosis. Osteoporosis is a
disease characterized by low bone mass and density and by structural
deterioration of bone tissue, causing bone fragility and increased
susceptibility to fractures, especially of the hip, spine, and
wrist. It is the underlying cause of most bone fractures in elderly
people. In the U.S. today, over 10 million people already have
osteoporosis and 18 million have low bone mass, placing them at
increased risk for the disease.1 Studies have shown
that calcium helps improve bone density2 and reduce
the incidence of fractures.2,3 Based on risk reduction
observed in three trials, researchers have estimated that in the
U. S. in 1995 alone, 134,764 hip fractures and $2.6 billion in
direct medical costs could have been avoided if individuals over
age 50 had supplemented 1,200 mg of calcium per day.3
Other Functions
Because calcium is required for muscle contraction, it is essential
for the function of all muscles, including the heart. There is
evidence that calcium, along with potassium and magnesium, may
help protect salt-sensitive individuals from developing hypertension.
4 Some studies suggest that calcium also may play a
role in the prevention of colorectal cancer.5-7 Other
studies have failed to demonstrate a significant association between
calcium consumption and cancer risk, but have suggested a possible
role for vitamin D in this area. 8,9
Dosage/toxicity
The optimum daily intake of calcium varies with age and gender.
The recommendations from a 1994 consensus statement issued by
the National Institutes of Health are:
| From birth to six months: |
400 mg/day |
| Ages six to twelve months: |
600 mg/day |
| Ages one to five years: |
800 mg/day |
| Ages six to ten years: |
800-1,200 mg/day |
| Ages 11 to 24 years |
1,200-1,500 mg/day |
| Women 25-50 years: |
1,000 mg/day |
| Pregnant or lactating women: |
1,200-1,500 mg/day |
| Postmenopausal women on estrogen
replacement therapy: |
1,000 mg/day |
| Postmenopausal women not on estrogen
replacement therapy: |
1,500 mg/day |
| Men age 25-65: |
1,000 mg/day |
| Men and women over 65: |
1,500 mg/day |
Calcium intake of 2,000 mg/day appears to be safe in most people.
These guidelines are based on calcium from diet plus any calcium
taken in supplemental form.10 Adequate vitamin D is
essential for optimal calcium absorption. New guidelines recommend
that adults between the ages of 51 and 70 consume at least 400
IU of vitamin D per day and that those over 70 consume 600 IU
per day.11 For best absorption, calcium supplements
should be taken with meals. Complications from excessive calcium
intake are rare, as excess calcium is usually not absorbed. Patients
with with hyperparathyroidism or cancer should not take calcium
supplements unless under a physician's supervision.12
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