Calcium, 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 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 .
The remaining 99% of the body’s calcium supply is stored in the bones and teeth where it supports their structure and function . 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 periods of growth in children and adolescents, 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 .
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; often used to plan nutritionally adequate diets for individuals.
- Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA.
- Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals.
Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.
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 United States . 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 are listed in Table 2.
|Table 2: Selected Food Sources of Calcium |
|Yogurt, plain, low fat, 8 ounces||415||42|
|Mozzarella, part skim, 1.5 ounces||333||33|
|Sardines, canned in oil, with bones, 3 ounces||325||33|
|Yogurt, fruit, low fat, 8 ounces||313–384||31–38|
|Cheddar cheese, 1.5 ounces||307||31|
|Milk, nonfat, 8 ounces**||299||30|
|Soymilk, calcium-fortified, 8 ounces||299||30|
|Milk, reduced-fat (2% milk fat), 8 ounces||293||29|
|Milk, buttermilk, lowfat, 8 ounces||284||28|
|Milk, whole (3.25% milk fat), 8 ounces||276||28|
|Orange juice, calcium-fortified, 6 ounces||261||26|
|Tofu, firm, made with calcium sulfate, ½ cup***||253||25|
|Salmon, pink, canned, solids with bone, 3 ounces||181||18|
|Cottage cheese, 1% milk fat, 1 cup||138||14|
|Tofu, soft, made with calcium sulfate, ½ cup***||138||14|
|Ready-to-eat cereal, calcium-fortified, 1 cup||100–1,000||10–100|
|Frozen yogurt, vanilla, soft serve, ½ cup||103||10|
|Turnip greens, fresh, boiled, ½ cup||99||10|
|Kale, fresh, cooked, 1 cup||94||9|
|Ice cream, vanilla, ½ cup||84||8|
|Chinese cabbage, bok choi, raw, shredded, 1 cup||74||7|
|Bread, white, 1 slice||73||7|
|Pudding, chocolate, ready to eat, refrigerated, 4 ounces||55||6|
|Tortilla, corn, ready-to-bake/fry, one 6” diameter||46||5|
|Tortilla, flour, ready-to-bake/fry, one 6” diameter||32||3|
|Sour cream, reduced fat, cultured, 2 tablespoons||31||3|
|Bread, whole-wheat, 1 slice||30||3|
|Kale, raw, chopped, 1 cup||24||2|
|Broccoli, raw, ½ cup||21||2|
|Cheese, cream, regular, 1 tablespoon||14||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 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. The U.S. Department of Agriculture’s (USDA’s) Nutrient Database Web site lists the nutrient content of many foods and provides comprehensive list of foods containing calcium arranged by nutrient content and by food name.
** 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.
In its food guidance system, MyPlate, the U.S. Department of Agriculture recommends that persons aged 9 years and older eat 3 cups of foods from the milk group per day . A cup is equal to 1 cup (8 ounces) of milk, 1 cup of yogurt, 1.5 ounces of natural cheese (such as Cheddar), or 2 ounces of processed cheese (such as American).