The remaining 99% of the body's calcium supply is stored in the bones and teeth where it supports their structure and function [1]. 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 [1].
Recommended Intakes
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) [1]. 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 [1].
| Age | Male | Female | Pregnant | Lactating |
|---|---|---|---|---|
| 0–6 months* | 200 mg | 200 mg | ||
| 7–12 months* | 260 mg | 260 mg | ||
| 1–3 years | 700 mg | 700 mg | ||
| 4–8 years | 1,000 mg | 1,000 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 |
| 51–70 years | 1,000 mg | 1,200 mg | ||
| 71+ years | 1,200 mg | 1,200 mg |
* Adequate Intake (AI)
Sources of Calcium
FoodMilk, yogurt, and cheese are rich natural sources of calcium and are the major food contributors of this nutrient to people in the United States [1]. 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.
| Food | Milligrams (mg) per serving |
Percent DV* |
|---|---|---|
| Yogurt, plain, low fat, 8 ounces | 415 | 42 |
| Orange juice, calcium-fortified, 6 ounces | 375 | 38 |
| Yogurt, fruit, low fat, 8 ounces | 338–384 | 34–38 |
| Mozzarella, part skim, 1.5 ounces | 333 | 33 |
| Sardines, canned in oil, with bones, 3 ounces | 325 | 33 |
| Cheddar cheese, 1.5 ounces | 307 | 31 |
| Milk, nonfat, 8 ounces** | 299 | 30 |
| Milk, reduced-fat (2% milk fat), 8 ounces | 293 | 29 |
| Milk, buttermilk, 8 ounces | 282–350 | 28–35 |
| Milk, whole (3.25% milk fat), 8 ounces | 276 | 28 |
| 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 |
| Instant breakfast drink, various flavors and brands, powder prepared with water, 8 ounces | 105–250 | 10–25 |
| Frozen yogurt, vanilla, soft serve, ½ cup | 103 | 10 |
| Ready-to-eat cereal, calcium-fortified, 1 cup | 100–1,000 | 10–100 |
| Turnip greens, fresh, boiled, ½ cup | 99 | 10 |
| Kale, fresh, cooked, 1 cup | 94 | 9 |
| Kale, raw, chopped, 1 cup | 90 | 9 |
| Ice cream, vanilla, ½ cup | 84 | 8 |
| Soy beverage, calcium-fortified, 8 ounces | 80–500 | 8–50 |
| 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 |
| 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 Nutrient Database Web site lists the nutrient content of many foods. It also provides a comprehensive list of foods containing calcium.
** 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 [3].
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).** 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.
Dietary supplements
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 [4]. Calcium citrate is also useful for people with achlorhydria, inflammatory bowel disease, or absorption disorders [1]. Other calcium forms in supplements or fortified foods include gluconate, lactate, and phosphate. Calcium citrate malate is a well-absorbed form of calcium found in some fortified juices [5].
Calcium supplements contain varying amounts of elemental calcium. For example, calcium carbonate is 40% calcium by weight, whereas calcium citrate is 21% calcium. Fortunately, elemental calcium is listed in the Supplement Facts panel, so consumers do not need to calculate the amount of calcium supplied by various forms of calcium supplements.
The percentage of calcium absorbed depends on the total amount of elemental calcium consumed at one time; as the amount increases, the percentage absorption decreases. Absorption is highest in doses ≤500 mg [1]. So, for example, one who takes 1,000 mg/day of calcium from supplements might split the dose and take 500 mg at two separate times during the day.
Some individuals who take calcium supplements might experience gastrointestinal side effects including gas, bloating, constipation, or a combination of these symptoms. Calcium carbonate appears to cause more of these side effects than calcium citrate [1], so consideration of the form of calcium supplement is warranted if these side effects are reported. Other strategies to alleviate symptoms include spreading out the calcium dose throughout the day and/or taking the supplement with meals.
