Calcium is a mineral found mainly in the hard part of bones, where it is stored. Calcium is added to bones by cells called osteoblasts and is removed from bones by cells called osteoclasts. It is the most abundant mineral in the body, is found in some foods, added to others, available as a dietary supplement, and present in some medicines (such as antacids). Calcium is essential for healthy bones. It is also important for muscle contraction, blood vessel expansion and contraction, secretion of hormones and enzymes, transmitting impulses throughout the nervous system and normal blood clotting. The body strives to maintain constant concentrations of calcium in blood, muscle, and intercellular fluids, though less than 1% of total body calcium is needed to support these functions.

The remaining 99% of the body's calcium supply is stored in the bones and teeth where it supports their structure. Bone itself undergoes continuous remodeling, with constant resorption and deposition of calcium into new bone. The balance between bone resorption and deposition changes with age. Bone formation exceeds resorption in growing children, whereas in early and middle adulthood both processes are relatively equal. In aging adults, particularly among postmenopausal women, bone breakdown exceeds formation, resulting in bone loss that increases the risk of osteoporosis over time.

Bones are living tissue. Our bodies continually remove and replace small amounts of calcium from our bones as they grow. If more calcium is removed than is replaced, bones become weaker and have a greater chance of breaking. If you get enough calcium from the foods you eat and drink, your body doesn’t have to take the calcium from your bones and bones can stay strong. In fact, getting enough calcium when you’re young can help prevent osteoporosis, a condition that makes bones weak and more likely to break. Calcium also can help build strong teeth.  Both baby teeth and adult teeth need calcium to grow and develop.  Calcium can also help protect teeth against tooth decay.  Calcium also helps make gums healthy and makes jawbones strong too. 

Chemically calcium is reactive and soft for a metal (though harder than lead, it can be cut with a knife with difficulty). It is a silvery metallic element that must be extracted by electrolysis from a fused salt like calcium chloride. Once produced, it rapidly forms a gray-white oxide and nitride coating when exposed to air. It is somewhat difficult to ignite, unlike magnesium, but when lit, the metal burns in air with a brilliant high-intensity red light. Calcium metal reacts with water, evolving hydrogen gas at a rate rapid enough to be noticeable, but not fast enough at room temperature to generate much heat.

According to the National Academy of Sciences, adequate intake of calcium is 1,200 milligrams a day (four glasses of milk) for men and women 51 and older, 1,000 milligrams a day for adults 19 to 50, and 1,300 milligrams a day for children 9 to 18. The upper limit for calcium intake is 2.5 grams daily.

Intake recommendations for calcium and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences).. DRI is the general term for a set of reference values used for planning and assessing the nutrient intakes of healthy people. These values, which vary by age and gender, include:

  • Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy individuals.
  • Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
  • Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.
The FNB established AIs for the amounts of calcium required to maintain adequate rates of calcium retention and bone health in healthy people. They are listed in Table 1 in milligrams (mg) per day.

Adequate Intakes (AIs) for Calcium
Age Male Female Pregnant Lactating
Birth to 6 months 210 mg 210 mg    
7-12 months 270 mg 270 mg    
1-3 years 500 mg 500 mg    
4-8 years 800 mg 800 mg    
9-13 years 1,300 mg 1,300 mg    
14-18 years 1,300 mg 1,300 mg 1,300 mg 1,300 mg
19-50 years 1,000 mg 1,000 mg 1,000 mg 1,000 mg
50+ years 1,200 mg 1,200 mg    

mg = milligrams

Food sources of calcium include dairy foods, some leafy green vegetables such as broccoli and collards, canned salmon, clams, oysters, calcium-fortified foods, and tofu. Milk, yogurt, and cheese are rich sources of calcium and are the major food contributors of this nutrient to people in the United States. Non-dairy sources include vegetables, such as Chinese cabbage, kale, and broccoli. Most grains do not have high amounts of calcium unless they are fortified; however, they contribute calcium to the diet because they do have small amounts and people consume them frequently. Foods fortified with calcium include many fruit juices and drinks, tofu, and cereals. Selected food sources of calcium are listed in Table 2.

Selected Food Sources of Calcium
Food Milligrams (mg) per serving Percent DV*
Yogurt, plain, low fat, 8 ounces 415 42
Sardines, canned in oil, with bones, 3 ounces 324 32
Cheddar cheese, 1.5 ounces 306 31
Milk, nonfat, 8 ounces 302 30
Milk, reduced-fat (2% milk fat), 8 ounces 297 30
Milk, lactose-reduced, 8 ounces 285-302 29-30
Milk, whole (3.25% milk fat), 8 ounces 291 29
Milk, buttermilk, 8 ounces 285 29
Mozzarella, part skim, 1.5 ounces 275 28
Yogurt, fruit, low fat, 8 ounces 245-384 25-38
Orange juice, calcium-fortified, 6 ounces 200-260 20-26
Tofu, firm, made with calcium sulfate, ˝ cup 204 20
Salmon, pink, canned, solids with bone, 3 ounces 181 18
Pudding, chocolate, instant, made with 2% milk, ˝ cup 153 15
Cottage cheese, 1% milk fat, 1 cup unpacked 138 14
Tofu, soft, made with calcium sulfate, ˝ cup 138 14
Spinach, cooked, ˝ cup 120 12
Ready-to-eat cereal, calcium-fortified, 1 cup 100-1,000 10-100

Instant breakfast drink, various flavors and brands, powder
prepared with water, 8 ounces

105-250 10-25
Frozen yogurt, vanilla, soft serve, ˝ cup 103 10
Turnip greens, boiled, ˝ cup 99 10
Kale, cooked, 1 cup 94 9
Kale, raw, 1 cup 90 9
Ice cream, vanilla, ˝ cup 85 8.5
Soy beverage, calcium-fortified, 8 ounces 80-500 8-50
Chinese cabbage, raw, 1 cup 74 7
Tortilla, corn, ready-to-bake/fry, 1 medium 42 4
Tortilla, flour, ready-to-bake/fry, one 6" diameter 37 4
Sour cream, reduced fat, cultured, 2 tablespoons 32 3
Bread, white, 1 ounce 31 3
Broccoli, raw, ˝ cup 21 2
Bread, whole-wheat, 1 slice 20 2
Cheese, cream, regular, 1 tablespoon 12 1

* DV = Daily Value. DVs were developed by the U.S. Food and Drug
Administration to help consumers compare the nutrient contents among
products within the context of a total daily diet.

The DV for calcium is 1,000 mg for adults and children aged 4 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.

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