Calcium: Reference and Dietary Sources

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Abstract

In this article, we describe:

  • the major purposes of this specific nutrient in the human body, 
  • its experimentally confirmed health uses, 
  • conventional ways to estimate nutrient status,
  • nutrient’s toxicities and deficiencies,
  • experimentally confirmed and approved levels of the nutrient intake for different demographics,
  • dietary sources of the nutrient.

Introduction

Calcium, the most abundant mineral in the body, 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 homeostatic concentrations of calcium in blood, muscle, and intercellular fluids. The remaining 99% of the body’s calcium supply is stored in the bones and teeth where it supports their structure and function.

Not all calcium consumed is actually absorbed in the gut. Humans absorb about 30% of the calcium in foods, but this varies depending upon the type of food consumed. Other factors also affect calcium absorption include amount consumed; age and life stage (absorption decreases to 15%–20% in adulthood, increases during pregnancy, and continues to decrease as people age); vitamin D intake; other components in food (phytic acid and oxalic acid, found naturally in some plants, bind to calcium and can inhibit its absorption). In contrast, wheat products (with the exception of wheat bran) do not appear to lower calcium absorption.

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; stimulants (caffeine and alcohol) intake; consumption of fruits and vegatables. 

There are two tests to measure blood calcium. The total calcium test measuresboth the free and bound forms. The ionized calcium test measures only the free, metabolically active form. 

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 (such as diuretics). 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.

Although frank calcium deficiency is uncommon, dietary intakes of the nutrient below recommended levels might have negative health consequences over the long term. The following groups are among those most likely to need extra calcium: postmenopausal women; amenorrheic women and the female athlete triad; individuals with lactose intolerance or cow’s milk allergy; and vegetarians.

Many claims are made about calcium’s potential benefits in health promotion and disease prevention and treatment: bone health and osteoporosis; cardiovascular disease; hypertension and preeclampsia; blood pressure regulation and hypertension; cancers of the colon, rectum, and prostate; kidney stones; and weight management.

Excessively high levels of calcium in the blood known as hypercalcemia can cause renal insufficiency, vascular and soft tissue calcification, hypercalciuria (high levels of calcium in the urine) and kidney stones. Although very high calcium intakes have the potential to cause hypercalcemia, it is most commonly associated with primary hyperparathyroidism or malignancy.

Some evidence links higher calcium intake with increased risk of prostate cancer, but this effect is not well understood, in part because it is challenging to separate the potential effect of dairy products from that of calcium. Some studies also link high calcium intake, particularly from supplements, with increased risk of cardiovascular disease.

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Recommended Dietary Allowances (RDAs) for Calcium

AgeMaleFemalePregnantLactating
0–6 months*200 mg200 mg
7–12 months*260 mg260 mg
1–3 years700 mg700 mg
4–8 years1,000 mg1,000 mg
9–13 years1,300 mg1,300 mg
14–18 years1,300 mg1,300 mg1,300 mg1,300 mg
19–50 years1,000 mg1,000 mg1,000 mg1,000 mg
51–70 years1,000 mg1,200 mg
71+ years1,200 mg1,200 mg

* Adequate Intake (AI)

Dietary Sources of Calcium

Milk, yogurt, and cheese are rich natural sources of calcium and are the major food contributors of this nutrient to people in the developed countries. Nondairy sources include vegetables, such as Chinese cabbage, kale, and broccoli. Spinach provides calcium, but its bioavailability is poor. Most grains do not have high amounts of calcium unless they are fortified; however, they contribute calcium to the diet because they contain small amounts of calcium and people consume them frequently. Foods fortified with calcium include many fruit juices and drinks, tofu, and cereals.

 Selected Food Sources of Calcium

FoodMilligrams (mg) per servingPercent DV*
Plain low fat yogurt, 8 ounces41532
Orange juice, calcium-fortified, 1 cup34927
Mozzarella cheese, 1.5 ounces33326
Canned in oil sardines with bones, 3 ounces32525
Cheddar cheese, 1.5 ounces30724
Non-fat milk, 1 cup29923
Soymilk, calcium-fortified, 1 cup29923
Milk, reduced-fat (2%), 1 cup29323
Buttermilk, 1 cup28422
Whole milk (3.25%), 1 cup27621
Fruit yogurt, low fat, 6 ounces25820
Firm tofu, with calcium sulfate, ½ cup***25319
Canned with bone pink salmon, 3 ounces18114
Cottage cheese 1% milk fat, 1 cup13811
Soft tofu, with calcium sulfate, ½ cup***13811
Ready-to-eat cereal, calcium-fortified, 1 cup13010
Frozen yogurt, ½ cup1038
Cooked turnip greens, ½ cup998
Cooked kale, 1 cup947
Ice cream, ½ cup846
Chinese cabbage (bok chow), raw, 1 cup746
White bread, 1 slice736
Chocolate pudding ready to eat, 4 ounces555
Corn tortilla, 1 – 6” diameter464
Flour tortilla, 1 – 6” diameter322
Sour cream, cultured, 2 tablespoons312
Whole wheat bread, 1 slice302
Raw kale, 1 cup242
Raw broccoli, ½ cup212
Cream-cheese, 1 tablespoon141

* DV = Daily Value. The DV for calcium used above is 1,300 mg for adults and children aged 4 years and older. Foods providing 20% of more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.
** Calcium content varies slightly by fat content; the more fat, the less calcium the food contains.
*** Calcium content is for tofu processed with a calcium salt. Tofu processed with other salts does not provide significant amounts of calcium.

References

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