Calcium is the most abundant mineral in the human body.[1] Calcium is required for vascular contraction and vasodilation, muscle function, nerve transmission, intracellular signaling and hormonal secretion, though less than 1% of total body calcium is needed to support these critical metabolic functions. Serum calcium is very tightly regulated and does not fluctuate with changes in dietary intakes; the body uses bone tissue as a reservoir for, and source of calcium, to maintain constant concentrations of calcium in blood, muscle, and intercellular fluids[2] thus osteoporosis (loss of bone density) becomes a problem if prolonged calcium deficiency is experienced.


Symptoms of Calcium Deficiency:

Inadequate intakes of dietary calcium from food and supplements produce no obvious symptoms in the short term. Circulating blood levels of calcium are tightly regulated. Hypocalcemia results primarily from medical problems or treatments, including renal failure, surgical removal of the stomach, and use of certain medications. Symptoms of hypocalcemia include numbness and tingling in the fingers, muscle cramps, convulsions, lethargy, poor appetite, and abnormal heart rhythms. If left untreated, calcium deficiency leads to death.

Over the long term, inadequate calcium intake causes osteopenia which if untreated can lead to osteoporosis. The risk of bone fractures also increases, especially in older individuals. Calcium deficiency can also cause rickets, though it is more commonly associated with vitamin D deficiency

Anatomy of Absorption:

You are at increased risk of calcium deficiency if you have trouble absorbing fats, are taking prednisone, have extensive inflammation throughout your small intestines, or have had extensive removal of the small intestines.[3]

The two main forms of calcium in supplements are carbonate and citrate. Calcium carbonate is more commonly available and is both inexpensive and convenient. Due to its dependence on stomach acid for absorption, calcium carbonate is absorbed most efficiently when taken with food, whereas calcium citrate is absorbed equally well when taken with or without food. Calcium citrate is also useful for people with achlorhydria, inflammatory bowel disease, or absorption disorders.[2]

Factors That Affect Calcium Absorption

  • Amount consumed: the efficiency of absorption decreases as calcium intake increases.
  • Age and life stage: net calcium absorption is as high as 60% in infants and young children, who need substantial amounts of the mineral to build bone. Absorption decreases to 15%20% in adulthood (though it is increased during pregnancy) and continues to decrease as people age; compared with younger adults, recommended calcium intakes are higher for females older than 50 years and for both males and females older than 70 years.
  • Vitamin D intake: this nutrient, obtained from food and produced by skin when exposed to sunlight of sufficient intensity, improves calcium absorption.
  • Other components in food: phytic acid and oxalic acid, found naturally in some plants, bind to calcium and can inhibit its absorption. Foods with high levels of oxalic acid include spinach, collard greens, sweet potatoes, rhubarb, and beans. Among the foods high in phytic acid are fiber-containing whole-grain products and wheat bran, beans, seeds, nuts, and soy isolates. The extent to which these compounds affect calcium absorption varies. Research shows, for example, that eating spinach and milk at the same time reduces absorption of the calcium in milk [10]. In contrast, wheat products (with the exception of wheat bran) do not appear to lower calcium absorption. For people who eat a variety of foods, these interactions probably have little or no nutritional consequence and, furthermore, are accounted for in the overall calcium DRIs, which factor in differences in absorption of calcium in mixed diets.

    Some absorbed calcium is eliminated from the body in urine, feces, and sweat. This amount is affected by such factors as the following:
  • Sodium and protein intakes: high sodium intake increases urinary calcium excretion. High protein intake also increases calcium excretion and was therefore thought to negatively affect calcium status. However, more recent research suggests that high protein intake also increases intestinal calcium absorption, effectively offsetting its effect on calcium excretion, so whole body calcium retention remains unchanged.
  • Caffeine intake: this stimulant in coffee and tea can modestly increase calcium excretion and reduce absorption. One cup of regular brewed coffee, for example, causes a loss of only 23 mg of calcium. Moderate caffeine consumption (1 cup of coffee or 2 cups of tea per day) in young women has no negative effects on bone.
  • Alcohol intake: alcohol intake can affect calcium status by reducing its absorption and by inhibiting enzymes in the liver that help convert vitamin D to its active form. However, the amount of alcohol required to affect calcium status and whether moderate alcohol consumption is helpful or harmful to bone is unknown.
  • Phosphorus intake: the effect of this mineral on calcium excretion is minimal. Several observational studies suggest that consumption of carbonated soft drinks with high levels of phosphate is associated with reduced bone mass and increased fracture risk. However, the effect is probably due to replacing milk with soda rather than the phosphorus itself.
  • Fruit and vegetable intakes: metabolic acids produced by diets high in protein and cereal grains increase calcium excretion. Fruits and vegetables, when metabolized, shift the acid/base balance of the body towards the alkaline by producing bicarbonate, which reduces calcium excretion. However, it is unclear if consuming more fruits and vegetables affects bone mineral density. These foods, in addition to reducing calcium excretion, could possibly reduce calcium absorption from the gut and therefore have no net effect on calcium balance.

Medications that Interact with Calcium

*This is not an exhaustive list. Please check with your physician regarding interactions with medications you are taking*
Antacids that contain Aluminum [4]
Antibiotics (ex. Cipro - Ciprofloxacin, Doxycycline, Gentamicin, Levofloxacin, Minocycline, Norfloxacin, Ofloxacin, Tetracycline)[4]
Beta - Blocker Medication (ex. Atenolol / Tenormin) for blood pressure[4]
Bile Acid Sequesterants (ex. Cholestyramine, Colesevelam, Colestipol)[4]
Calcium Channel Blockers (ex. Verapamil)[4]
Cardiovascular (ex. Digoxin)[4]
Diuretics [Potassium Sparing (ex. Amiloride), Loop (ex. Bumetanide, Furosemide), Thiazide (ex. Hydrochlorothiazide)][4]
Hormones (ex. Estrogen)[4]
Osteoperosis Medications (ex. Alendronate)[4]
Anti-Siezure Medications (ex. Dilantin / Penytoin, Carbamazepine, Phenobarbitol, Primidone)[4]
Steroids (ex. Prednisone)[4]

Recommended Daily Intake:

Please see the chart below for recommended daily intake for calcium:

Natural Sources of Calcium:

Milk, yogurt, cheese, kale, broccoli, Chinese cabbage, canned salmon/sardines (from the bones of the fish), chia seeds

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