Benefits: Maintains normal heartbeat, nerve and muscle function and blood clotting.
Good food sources: Milk products, green leafy vegetables, canned salmon with bones and sardines with bones, calcium-fortified orange juice, corn tortillas processed with lime.
Cautions: Consult your doctor if you have: kidney disease, chronic constipation, colitis, diarrhea, stomach or intestinal bleeding, irregular heartbeat.
Substance interactions: Taking calcium with digitalis may result in heartbeat irregularities. Calcium decreases the absorption of iron supplements unless vitamin C is taken at same time. Increases blood level of both calcium and magnesium-containing medications or supplements. Oral contraceptives and estrogens may increase calcium absorption. Potassium supplements increases chance of heartbeat irregularities. Decreases absorption of tetracycline. Mega-doses of vitamin A stimulates bone loss. Mega-doses of vitamin D excessively increases absorption of calcium supplements.
Signs of toxicity: Severe nausea vomiting. Extremely low blood pressure. Extreme muscle weakness. Slow or irregular heartbeat.* Recommended daily intake levels, per the Consensus Development Conference of the National Institutes of health in Bethesda, Maryland:
Infants, up to age 6 months: 400 milligrams
Infants, ages 6 to 11 months: 600 milligrams
Children, ages 1 to 10 years: 800 to 1200 milligrams
Adolescents and young adults, ages 11 to 24: 1200 to 1500 milligrams
Men, ages 25 to 65: 1000 milligrams
Women, ages 25 to 50: 1000 milligrams
Pregnant and nursing women: 1200 to 1500 milligrams
Women at menopause (ages 51 to 65) who are taking estrogen: 1000 milligrams
Women at menopause (ages 51 to 65) who are not taking estrogen: 1500 milligrams
Men and women over age 65: 1500 milligrams
* Calcium in the foods you eat is absorbed through the small intestine and into the blood. The amount of calcium in the blood is regulated by parathyroid hormone. When calcium intake is low, the hormone signals for bone to be broken down, releasing calcium into the blood stream. With adequate calcium levels in the blood, we produce less hormone, so we conserve more calcium and more bone. Calcium then combines with phosphorus to help form hard substances that create the frame for strong bones and teeth.
* Avoid natural calcium carbonate and dolomite, which are natural forms of calcium, but may contain lead and aluminum. Pharmaceutical-grade calcium carbonate is free of contaminates. Calcium gluconate, lactate and citrate are metal-free, but they contain less concentrated forms of calcium. Calcium carbonate is found in several types of antacids (i.e. Tums, Rolaids), but avoid antacids which contain aluminum.
* Take supplements with food, however, high-fiber wheat bran cereals can reduce absorption by a fourth.
* When taking more than 500 mg of calcium, split it up and take it throughout the day. The body has trouble absorbing more than 500 mg at a time. Taking more than 2000 mg per day may cause constipation and kidney stones and inhibit zinc and iron absorption.
* Take calcium with the same amount of magnesium for maximum benefit. If the magnesium has a laxative effect, reduce the dosage.