Benefits / uses
Bone health and osteoporosis
Bones increase in size and mass during periods of growth in childhood and adolescence, reaching peak bone mass around age 30. The greater the peak bone mass, the longer one can delay serious bone loss with increasing age. Everyone should therefore consume adequate amounts of calcium and vitamin D throughout childhood, adolescence, and early adulthood. Osteoporosis, a disorder characterized by porous and fragile bones, is a serious public health problem for more than 10 million U.S. adults, 80% of whom are women. Osteoporosis is most associated with fractures of the hip, vertebrae, wrist, pelvis, ribs, and other bones. Supplementation with calcium plus vitamin D has been shown to be effective in reducing fractures and falls in institutionalized older adults.

When calcium intake is low or ingested calcium is poorly absorbed, bone breakdown occurs as the body uses its stored calcium to maintain normal biological functions. Bone loss also occurs as part of the normal aging process, particularly in postmenopausal women due to decreased amounts of estrogen. Many factors increase the risk of developing osteoporosis, including being female, thin, inactive, or of advanced age; smoking cigarettes; drinking excessive amounts of alcohol and having a family history of osteoporosis.

Although osteoporosis affects individuals of all races, ethnicities, and both genders, women are at highest risk because their skeletons are smaller than those of men and because of the accelerated bone loss that accompanies menopause. Regular exercise and adequate intakes of calcium and vitamin D are critical to the development and maintenance of healthy bones throughout the life cycle.

Cardiovascular disease
Calcium has been proposed to help reduce cardiovascular disease risk by decreasing intestinal absorption of lipids, increasing lipid excretion, lowering cholesterol levels in the blood and promoting calcium influx into cells. In the Iowa Women's Health Study, higher calcium intake was associated with reduced ischemic heart disease mortality in postmenopausal women.

Blood pressure and hypertension
Several clinical trials have demonstrated a relationship between increased calcium intakes and both lower blood pressure and risk of hypertension Other observational and experimental studies suggest that individuals who eat a vegetarian diet high in minerals (such as calcium, magnesium, and potassium) and fiber and low in fat tend to have lower blood pressure. The Dietary Approaches to Stop Hypertension (DASH) study was conducted to test the effects of three different eating patterns on blood pressure: a control "typical" American diet; one high in fruits and vegetables; and a third diet high in fruits, vegetables, and low-fat dairy products. The diet containing dairy products resulted in the greatest decrease in blood pressure

Cancer of the colon and rectum
Several studies have found that higher intakes of calcium from foods (low-fat dairy sources) and/or supplements are associated with a decreased risk of colon cancer. In a follow-up study to the Calcium Polyp Prevention Study, supplementation with calcium carbonate led to reductions in the risk of adenoma (a nonmalignant tumor) in the colon, a precursor to cancer, even as long as 5 years after the subjects stopped taking the supplement. In two large prospective epidemiological trials, men and women who consumed 700-800 mg per day of calcium had a 40%-50% lower risk of developing left-side colon cancer.
In the Women's Health Initiative, a clinical trial involving 36,282 postmenopausal women, daily supplementation with 1,000 mg of calcium and 400 IU of vitamin D3 for 7 years produced no significant differences in the risk of invasive colorectal cancer compared to placebo.

Weight management
Several studies have linked higher calcium intakes to lower body weight or less weight gain over time. Two explanations have been proposed. First, high calcium intakes might reduce calcium concentrations in fat cells by decreasing the production of two hormones (parathyroid hormone and an active form of vitamin D) that increase fat breakdown in these cells and discourage fat accumulation.

When To Take/Types To Take
Calcium supplements are best taken with meal. Since calcium cannot be absorbed without vitamin D, better supplements will include it. A daily intake of 400-600 IU of vitamin D would be ideal. Most experts agree that magnesium should also be present.
Which form of calcium is best? There is no simple answer to this question since there are many effective options. Some research has found that approximately the same level of absorption can be attained with various forms of calcium (including calsium citrate, clacium carbonate, hydroxypatite, calcium gluconolactate, and calcium pidolate), while other research has shown that certain forms of calcium (such as calcium citrate) are better absorbed over other forms (such as calcium gluconolactate and carbonate). Still other reserach shows that even calcium carbonate (a relatively insoluble form of calcium) is fairly well absorbed when taken with a meal.