Calcium

In terms of the quantities of mineral that should be taken daily, mineral are classified into two groups, macrominerals and trace minerals. "Macro" means large in Greek. That means we need a larger amount of macro minerals to sustain our normal and healthy cells.

Calcium (Ca)

Calcium, the most common macro-mineral in the human body. It takes up 1 to 2 percent of adult human body weight. Up to 99% of calcium is stored in bones and teeth. The mineral component of bone consists mainly of hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] crystals, which contain large amounts of calcium and phosphate. With hydroxyapatite crystals, bone is remodeled throughout life, going through two processes, bone formation and bone resorption. When bone formation exceeds bone resorption, a human has a normal growth. Conversely, when bone resorption chronically exceeds bone formation, a human is likely to suffer from osteoporosis.

In addition, about 1% of calcium is stored in the bloodstream and soft tissue, where the calcium plays a role in mediating vascular contraction and vasodilation, muscle contraction, nerve transmission, and glandular secretion. In order to preserve normal physiological function, the level of calcium in the blood must be maintained within a very narrow concentration range. When the amount of calcium intake becomes inadequate, the body will demineralize bone to keep up the level of normal blood calcium.

Daily Calcium Intake for Population

According to the Food and Nutrition Board of the National Academy of Sciences, kids who are 1 to 3 years old should intake calcium 500mg/day; kids who are 4 to 8 years old should intake calcium 800mg/day; kids who are 9 to 18 years old should intake 1,300 calcium mg/day; both men and women who are 19 to 50 years old should intake calcium 1200mg/day; pregnant and breast-feeding women who are 18 years old and younger should intake calcium 1300mg/day; pregnant and breast-feeding women who are 19 years old and older should intake calcium 1000mg/day.

List of Calcium Rich Foods

Food with Calcium	Serving size	Calcium per serving (mg)*
Dairy products
Milk	1 cup	290-300
Swiss cheese	1 oz (slice)	250-270
Yogurt	1 cup	240-400
American cheese	1 oz (slice)	165-200
Ice cream or frozen dessert	1/2 cup	90-100
Cottage cheese	1/2 cup	80-100
Parmesan cheese	1 Tbs	70
Powdered nonfat milk	1 tsp	50
Other
Sardines in oil (with bones)	3 oz	370
Canned salmon (with bones)	3 oz	170-210
Cabbage/ bok choy	1/2 cup	190
Broccoli	1 cup	160-180
Soybean curd (tofu)	4 oz	145-155
Turnip greens	1/2 cup, cooked	100-125
Kale	1/2 cup, cooked	90-100
Corn bread	2 1/2-in. square	80-90
Egg	1 medium	55
Orange	1/2 cup	52

Recently, multiple studies found that taking too much calcium supplements raises the risk of heart attack up to 30%. Do not rely on tablets to get calcium. Getting calcium from food sources is recommended.

Calcium Deficiency

Inadequate calcium intake or poor intestinal absorption leads to reduced bone mass and osteoporosis. Circulating ionized calcium has an interrelationship with parathyroid hormone synthesis and release. Once the blood calcium concentration goes below normal, parathyroid hormone fails to promote the reabsorption of calcium in the distal tubule at the kidneys. Thereupon, parathyroid hormone stimulates vitamin D to its active form (1,25-dihydroxyvitamin D) so that the absorption of calcium increases from the small intestine. Parathyroid hormone induces bone resorption and releases calcium into the bloodstream. Normal circulating calcium concentration is maintained by parathyroid hormone, which is done at the expense of skeletal mass.

Healthy Facts about Vegetarian Diets

In vegetarian diets, high contents of oxalate and phytate reduce calcium bioavailablity. This situation is balanced out by metabolizable anions which lower urinary calcium excretion. In comparison to omnivore diets containing animal protein, vegetarian diets have fairly similar dietary calcium intakes and similar amount of urinary calcium excretion.

Calcium Excess

A study found that higher doses of calcium supplements (1200mg/day in addition to 900mg/day from dietary sources) did cause constipation in 13% of the blinded trials.

Oxalate is a major component of kidney stone. Calcium can inhibit oxalate absorption from the intestines, so calcium has a protective effect. However, if the dose of calcium intake is too high, over 2,000mg/day, then the risk of nephrolithiasis (kidney stone formation) might increase.

Gastritis occasionally happens in some cases, which might be caused by taking calcium carbonate between meals. As a result, rebound acid production is stimulated.