Calcium

Calcium is one of the most abundant minerals in the human body, accounting for approximately 1.5% of total body weight. Ninety-nine percent of the bodys calcium is found in the bones and teeth with the remaining 1% being distributed in other areas.

A calcium-deficient diet is one of the causative factors involved in the development and progression of osteoporosis, a disease characterized by brittle and porous bones, which affects more than 20 million individuals in the United States. Because of the widespread prevalence of osteoporosis and calcium\'s role in this disease, there has has recently been a plethora of public health messages encouraging the public to consume foods rich in calcium.

Dairy products have been commonly thought to be significant sources of dietary calcium. While dairy foods do contain significant amounts of calcium, many calcium-rich plant-based foods may be preferable sources since they provide considerable amounts of calcium, yet feature lower caloric content than many dairy products.

Physiological functions of calcium

• Maintains healthy and strong bones
• Supports the proper functioning of nerves and muscles
• Helps in blood clotting processes

Physiological events that may signal a need for greater calcium intake

• Muscle pain or spasms
• Tingling or numbness in extremities (hands and feet)
• Frequent bone fractures
• Growth retardation and bone deformities in children

Functions of calcium

Calcium plays a critical role in maintaining bone strength and density. Calcium is involved in a process known as bone mineralization where it joins with phosphorous to form calcium phosphate, a major component of hydoxyapatite, the mineral complex that gives bones their structure and strength.

In addition to bone integrity, calcium plays a role in various other physiological activities including nerve conduction, muscle contraction, blood clotting, enzymatic activity regulation and cell membrane function. Since these physiological activities are essential to life, there are complex regulatory systems in place to tightly control the amount of calcium in the blood so that it can be available for these activities. Therefore, when dietary intake of calcium is too low, the body draws upon bone calcium stores to maintain normal blood concentrations of calcium. After many years, the extraction of the calcium from the bone to the blood can lead to osteoporosis.

Causes and symptoms of calcium deficiency

Insufficient dietary calcium intake, poor absorption and excessive calcium losses through the urine and feces can cause calcium deficiency. Hypochlorhydria (diminished stomach acid secretions) can reduce calcium absorption and lead to compromised calcium status. Hypochlorhydria occurs in many people and is especially common in the elderly and in individuals who regularly consume antacids. As vitamin D plays an integral role in the absorption and utilization of calcium, vitamin D deficiency or inability of the liver or kidneys to efficiently convert inactive vitamin D to its active form can result in impaired calcium status. Genetic polymorphisms in vitamin D3 receptors can also negatively affect calcium absorption. Vitamin D3 receptors mediate the actions of vitamin D3, which include increasing calcium absorption from the small intestine and increasing the activity of osteoblasts (bone forming cells)and mineralization of bone. Defects in the VDR gene may therefore lead to reduced peak bone mass as a young adult and to a more rapid decline in bone density after middle age.

In adults, calcium deficiency can result in osteomalacia (softening of the bones) and can also be a contributing factor to the development of osteoporosis. In children, calcium deficiency can lead to rickets, characterized by growth retardation and bone deformities, caused by improper bone mineralization.

Low blood levels of calcium, particularly free ionized calcium, can result in tetany, a condition that manifests in excessive nerve activity. Muscle pain and spasms as well as tingling and numbness in the hands and feet are symptoms of tetany.

Causes and symptoms of calcium toxicity

Hypercalcemia, elevated blood calcium levels, may result from excessive intakes of more than 3,000 milligrams of calcium per day. Hypercalcemia can lead to soft tissue calcification if occurring simultaneously with low blood phosphorous levels. Soft tissue calcification results from calcium accumulating in cells other than bone. In 1997, the Institute of Medicine at the National Academy of Sciences set the Tolerable Upper Intake Level (UL) for calcium at 2,5000 milligrams per day.

The effect of cooking, storage and processing on calcium

Neither cooking nor long-term food storage affects the level of calcium in foods.

Interactions between medications and calcium

Medications that impact the absorption, utilization, and/or excretion of calcium:

• Corticosteroids (i.e., hydrocortisone and prednisone)
  • reduce the bodys ability to activate vitamin D, resulting in decreased calcium absorption and increased calcium excretion in the urine
• Aluminum-containing antacids (i.e., Maalox^TM and Mylanta^TM)
  • may increase the urinary and stool loss of calcium
• Thyroid hormones
  • may increase urinary excretion of calcium
• Anticonvulsant medications (i.e., Dilantin^TM)
  • decrease the activity of vitamin D, resulting in decreased calcium absorption
• Antibiotics (including gentamicin, erythromycin, neomycin, isoniazid, sulfamethoxazole, tobramycin and cycloserine)
  • may interfere with calcium absorption and/or utilization
• Hormone replacement therapy
  • may decrease calcium excretion and increase calcium absorption in postmenopausal women

   

Calcium (especially from dietary supplements) may be compromised with the absorption of the following medications:

• Alendronate (Fosamax^TM)
  • Since most people who take alendronate also take calcium supplements, it is advisable to take Alendronate at least two hours before or after taking the calcium supplement.
• Tetracycline antiobiotics
  • Calcium from antacids, dairy products, and supplements can decrease its absorption, therefore reducing its effectiveness.

   

Interactions that occur between calcium and other nutrients

Nutrients that compromise the absorption, utilization, and/or excretion of calcium:

• Vitamin D
  • accelerates the absorption of calcium from the gastrointestinal tract
• Potassium
  • high intake reduces the urinary excretion of calcium
• Sodium
  • high intake causes an increase in the urinary excretion of calcium
• Caffeine
  • high intake causes an increase in the urinary excretion of calcium
• Protein
  • high intake causes an increase in the urinary excretion of calcium
• Dietary fiber, as found in wheat and oat bran
  • decreases transit time of food, thereby limiting the amount of time calcium has to be absorbed
  • stimulates proliferation of friendly intestinal flora, which binds calcium, making it less available for absorption
• Phytic acid, as found in whole grains, nuts, legumes and other foods
  • can form an insoluble complex by binding to calcium, thereby reducing calciums absorption, although the actual reduction of available calcium is relatively small
• Oxalic acid, as found in spinach, beets, celery, pecans, peanuts, tea, cocoa and other foods
  • can bind to calcium and form an insoluble complex that is excreted in the feces, although the actual reduction of available calcium is relatively small

   

Calcium impacts the absorption of the following nutrients:

• Heme and nonheme iron
• Magnesium
  • As calcium and magnesium compete for intestinal absorption, dietary supplements of these two minerals should not be taken at the same time.

   

Health conditions that require special emphasis on calcium

Individuals who have the following health conditions should pay special attention to their calcium status:

• Colon cancer
• Inflammatory bowel disease
• Hypertension
• Kidney stones
• Cataracts
• Osteoporosis
• Polycystic ovarian syndrome
• Pregnancy-induced hypertension and preeclampsia
• Premenstrual syndrome

Forms in which calcium is found in dietary supplements.

The different forms of calcium used in the manufacture of calcium supplements fall into three general categories: 1) naturally-derived calcium, also known as unrefined calcium carbonate 2) refined calcium carbonate and 3) chelated calcium.

Naturally-derived calcium is typically listed in dietary supplement labels as either bone meal, oyster shell, limestone or dolomite (clay). While these forms are typically less expensive, they carry greater risk as they may contain significant amounts of lead, which can cause toxicity effects to brain, kidney and red blood cells.

The most commonly used form of calcium is refined calcium carbonate. While relatively inexpensive in comparison to chelated calcium, it is also less well-absorbed. The presence of food in the stomach will cause the secretion of hydrochloric acid, which is necessary for the breakdown of calcium carbonate, therefore, to enhance absorption of this type of calcium, make sure that you take the supplements with meals.

When calcium is bound to an organic acid, such as malate, citrate, lactate or gluconate, or an amino acid, such as asparate, it is referred to as chelated calcium. Scientific research has shown that these chelated forms, especially calcium citrate, are more bioavailable than calcium carbonate. Hydroxyapatite, the phosphorous-containing compound of bone mineral matrix, is another form in which calcium is available in dietary supplements.

Supplemental calcium can be found in a variety of delivery forms including tablets, chewable tablets, capsules, chewable candies and fortified juices and foods.

Foods that are concentrated sources of calcium

Excellent sources of calcium include mustard greens, tofu (processed with calcium) and turnip greens. Very good sources of calcium include blackstrap molasses, cheddar cheese, cows milk, goats milk, kale, sesame seeds, Swiss chard and yogurt as well as herbs and spices such as basil, cinnamon, peppermint and thyme.