Calcium

Calcium, the most abundant mineral in the body, makes up 2% of the body weight and 39% of total body minerals. Approximately 99% of the calcium exists in the bones and teeth. The remaining 1% of calcium is in the blood and extracellular fluids and within the cells of all tissues, where it regulates many important metabolic functions. Bone is a dynamic tissue that returns calcium and other minerals to the extracellular fluids and blood on demand. Bone takes up calcium and other minerals from the blood when they are consumed. The calcium in teeth cannot be mobilized back to the blood because the minerals of erupted teeth are fixed for life. Late in life bone retention of calcium derived from food and supplements is limited unless the calcium is consumed along with sufficient vitamin D or bone-conserving drug. 

Adequate dietary calcium is needed to permit optimal gains in bone mass and density in the prepubertal and adolescent years. These gains are especially critical for girls because the accumulated bone may provide additional protection against osteoporosis in the years after menopause. Peak calcium retention by girls has been shown to occur in the prepubertal and early pubertal periods and is influenced by race with black girls having significantly higher retention rates.

Postmenopausal women need to obtain sufficient amounts of calcium to maintain bone health and suppress PTH (Parathyroid hormone), which increases later in life in most individuals, perhaps as a result of inadequate calcium in the diet. Additional amounts of calcium are recommended to meet the needs of pregnancy and lactation. 

Calcium is required for nerve transmission and regulation of heart muscle function. The proper balance of calcium, sodium, potassium, and magnesium maintains skeletal muscle tone and controls nerve irritability. A significant increase in the serum calcium level can cause cardiac or respiratory failure, whereas a decrease results in tetany of skeletal muscles.

Ionized calcium initiates the formation of a blood clot by stimulating the release of thromboplastin from blood platelets. 

High dietary calcium intakes are associated with decreased prevalence of overweight and obesity. The mechanism for this affect appears to be related to depression of the PTH and vitamin D, which leads to inhibition of lipogenesis and increased lipolysis, and increased excretion of fecal fat due to soaps formation.

Prolonged bed rest or periods of weightlessness during space travel promote significant calcium losses in response to a lack of tension or gravity on the bones. Older individuals who required a prolonged recovery with limited activity, such as those with hip fractures or other illnesses, also have increased calcium losses. Many studies have shown that physical activity promotes bone health.

Dietary reference intake

Infants 210-700 mg/day

Children 1000-1300 mg/day

Adolescents 1300 mg/day

Adults 1000-1200 mg/day

Pregnant 1000-1300 mg/day

Lactating 1000-1300 mg/day

Calcium content of selected foods

Milkshake, vanilla, 11 oz (457 mg)

Yogurt, low fat, with fruit, 1 cup (345 mg)

Fast-food enchilada, 1 (324 mg)

Rhubarb, cooked, ½ cup (318 mg)

Spinach, frozen, cooked, 1 cup (291 mg)

Milk, 2% milkfat, 1 cup (285 mg)

Cheese, cheddar, 1 oz (204 mg)

Salmon, canned, with bones, 3 ½ oz (181 mg)

Tofu, regular, ¼ block (163 mg)

Cheese, cottage, 1 cup (155 mg)

Almonds, 1 oz (70 mg)

Baked beans, white, ½ cup (64 mg)

Bread, whole wheat, 1 slice (20 mg)

Deficiency

Osteomalacia

Colon cancer

Hypertension (high blood pressure)

Osteoporosis

Toxicity

Hypercalcemia (calcification in soft tissues – kidneys)

Increased bone fractures in the elderly

Constipation

Interfere absorption of iron, zinc, manganese (calcium and these minerals should be taken at different times)