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CALCIUM

Calcium is an essential element. The body contains about one kilogram of calcium, of which 99% is stored in the bones and teeth. The remainder is distributed in various organs and tissues. Calcium is involved in a multitude of important functions, such as the release of neural transmitters and muscle contraction. There is a homeostasis between calcium ions in the bones and calcium ions in the bloodstream. Excessive calcium in blood is actively deposited into the bones, and calcium is readily released from the bones when the blood level of calcium becomes too low. Prolonged calcium insufficiency can bring about osteoporosis.

What Are the Major Functions of Calcium?

 • Bones and teeth. Bones are in a dynamic state and are constantly being repaired or rebuilt. All the calcium in your bones will be replaced within 8–12 years, but calcium in your teeth will never be replaced once deposited. The interplay between osteoblasts (bone-forming cells) and osteoclasts (bone-removing cells) in the bones is essential for maintaining bone health. Osteoblasts deposit calcium in the bones, and osteoclasts release calcium from the bones. During the growth phase in childhood, osteoblasts are actively adding calcium to the bones, while in patients with osteoporosis, osteoclasts are actively removing calcium from the bones.

 • Blood coagulation. Blood coagulation factors require calcium as a cofactor. Binding to calcium enables these blood coagulation factors to adhere to platelets. Without binding to calcium, these blood coagulation factors cannot form blood clots, causing uncontrollable bleeding.

 • Neurotransmitters. As the action potential (transporting electrical signals from one cell to the next) arrives, calcium ions stored in the neurons are released, which triggers the release of neurotransmitters, such as dopamine, to the neighboring neurons.

 • Muscle contraction. Muscle cells form muscle fibers, which are comprised of actin and myosin. Actin and myosin display a mutual attraction to each other. The binding of actin to myosin induces muscle contraction. In a resting state, troponin and tropomyosin sandwich themselves between actin and myosin to prevent actin from binding to myosin. When the brain sends a message for muscle contraction, calcium ions are quickly released and bind to troponin. Calcium binding to troponin causes the movement that removes troponin and tropomyosin from between actin and myosin, hastening the binding of actin to myosin and the subsequent muscle contraction.

What Are the Symptoms of Calcium Deficiency?

 • The major symptoms of calcium deficiency include fragile bones, impaired vision, atrial fibrillation, and osteoporosis.

What Are the Causes of Calcium Deficiency?

 • Diet. An unhealthy diet is the main cause of calcium deficiency. According to data from the USDA, 78% of women and 87% of teenage girls are calcium insufficient. Only 55% of men obtain sufficient calcium from foods. Hence it is not surprising that osteoporosis is now a serious health issue in the US.

 • Parathyroid hormone. Parathyroid hormones regulate calcium concentrations in the blood. Low blood calcium triggers the secretion of parathyroid hormones from the parathyroid gland. Parathyroid hormones then release calcium from the bones and elevate blood calcium levels. When blood calcium is too high, the body will attenuate the secretion of parathyroid hormones. Parathyroid hormone disorder can contribute to problems related to calcium deficiency.

Prevention and Treatment of Diseases

 • Prevention. Meta-analysis confirms that calcium can help prevent bone fractures (46), preeclampsia (97), and colorectal cancer (56).

 • Treatment. Calcium supplements help treat hypertension (78).

Which Food Items Are Calcium Rich?

Milk and other dairy products are excellent sources of calcium. Plant-based foods like broccoli, spinach, tofu, and nuts, as well as animal-based foods like eggs, sardines, and salmon, contain high amounts of calcium.

This list of calcium-rich food items is adapted from information provided by the NIH Office of Dietary Supplements.

Daily reference value of calcium is 1,000 mg according to the 2013 FDA food-labeling guidelines.

What Are the Recommended Dietary Allowances for Calcium?

The upper daily intake limit of calcium is 2,500 mg (19–50 years old) or 2,000 mg (51 years and older).

Calcium Supplements

 • Types. Calcium supplements come in different chemical formulations, including calcium carbonate, calcium citrate, calcium malate, calcium lactate, calcium gluconate, and the like. Among them, calcium carbonate is the least expensive—this is the form found in oyster shells and coral. It is easier for the intestines to absorb calcium citrate and calcium malate compared to calcium carbonate. Owing to high molecule weights, calcium lactate and calcium gluconate supplements are mainly available in large tablet sizes, which may contain less calcium per tablet.

 • Dosage. Calcium contents in calcium supplements often are not clearly stated on the label. For instance, based on their weights, calcium carbonate, calcium malate, and calcium gluconate contain only 40%, 21%, and 9% calcium, respectively. A 1-gram tablet of a calcium gluconate supplement may have only 90 mg of calcium. Read the label carefully for the calcium content of these products when purchasing.

 • Preteen and teenage girls. During growth and development, girls aged 9–18 should take 500 mg of calcium and 800 IU of vitamin D daily.

 • Women. Calcium supplementation can attenuate premenopausal syndromes, including mood swings, headaches, overeating, and bloating. It is recommended that premenopausal women take 1 g of calcium daily for three days before menstruation.

 • Bone fractures. Calcium plus vitamin D supplements prevent bone fractures. It is recommended that postmenopausal women take 500 mg of calcium and 400 IU of vitamin D daily to curtail the risk of bone fractures.

 • Hypertension. Calcium deficiency elevates the risk of hypertension. Calcium supplementation lowers systolic and diastolic pressure in hypertensive patients.

 • Life-span. Taking calcium supplements may extend the life-span. Studies from Canada have shown that postmenopausal women who took calcium supplements at a daily dose of 1 g for 10 years had a reduced rate of death from cardiovascular diseases.

 • Cholesterol. Taking daily supplements of calcium at a dose of 1 g for one year raises “good” cholesterol (HDL) and lowers “bad” cholesterol (LDL) in postmenopausal women.

Safety Issues

 • Overdose. Daily supplements of calcium at doses greater than 1,500 mg may increase the risk of prostate cancer and heart disease. On the other hand, calcium insufficiency also adds to the risk of prostate cancer.

 • Vitamin D. Vitamin D enhances calcium absorption in the intestines. It is beneficial to take calcium and vitamin D supplements together. A dose of 500 mg of calcium is absorbed very efficiently by the intestines. If a daily dose of 1,000 mg of calcium is needed, you may take 500 mg twice a day.

 • Diet. High-sodium and protein-rich diets may trigger overexcretion of calcium in the urine. People who enjoy salty and meaty meals need to be cautious about potential calcium deficiency.

What Types of Drugs May Interact with Calcium?

 • Diuretics. Diuretic drugs may enhance renal absorption of calcium, leading to problems associated with high blood calcium levels.

 • Digoxin. Heart failure patients who take digoxin together with calcium supplements may exacerbate the risk of atrial fibrillation.

 • Antibiotics. Taking calcium supplements may interfere with the absorption of tetracycline and other antibiotics by the intestines.

 • Other medications and supplements. Antacid drugs, corticosteroids, heparin, iron, manganese, and chromium all lower the absorption of calcium by the intestines.

 • Diabetes. Metformin interferes with the absorption of vitamin B12 by the intestines in type 2 diabetes patients. Calcium supplementation improves the absorption of vitamin B12. The suggested daily dose is 1 g of calcium.