Calcium Information

• What is Calcium
• Recommended Intakes for Calcium
• Sources of Calcium
• Calcium Intakes and Status
• Calcium Deficiency
• Groups at Risk of Calcium Inadequacy
• Calcium and Health
• Health Risks from Excessive Calcium
• Calcium Interactions with Medications
• Calcium and Healthy Diets

Calcium, the most abundant mineral in the body, is found in some foods, added to others, available as a dietary supplement. Calcium is required for muscle contraction, blood vessel expansion and contraction, secretion of hormones and enzymes, and transmitting impulses throughout the nervous system. 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.

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.

Table 1: 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

Milk, yogurt, and cheese are rich 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. 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.

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
Tofu, firm, made with calcium sulfate, ½cup***	204	20
Salmon, pink, canned, solids with bone, 3 ounces	181	18
Pudding, chocolate, instant, made with 2% milk, ½cup	153	15
Cottage cheese, 1% milk fat, 1 cup unpacked	138	14
Tofu, soft, made with calcium sulfate, ½cup***	138	14
Spinach, cooked, ½cup	120	12
Frozen yogurt, vanilla, soft serve, ½cup	103	10
Turnip greens, boiled, ½cup	99	10
Kale, cooked, 1 cup	94	9
Ice cream, vanilla, ½cup	85	8.5
Chinese cabbage, raw, 1 cup	74	7
Tortilla, corn, ready-to-bake/fry, 1 medium	42	4
Sour cream, reduced fat, cultured, 2 tablespoons	32	3
Bread, white, 1 ounce	31	3
Broccoli, raw, ½cup	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. ** 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, MyPyramid, 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).

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. Both the carbonate and citrate forms are similarly well absorbed, but individuals with reduced levels of stomach acid can absorb calcium citrate more easily. 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. The body absorbs calcium carbonate most efficiently when the supplement is consumed with food, whereas the body can absorb calcium citrate equally effectively when the supplement is taken with or without food.

Calcium supplements contain varying amounts of elemental calcium. For example, calcium carbonate is 40% calcium by weight, whereas calcium citrate is 21% calcium.

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. 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 gas, bloating, constipation, or a combination of these symptoms. Such symptoms can often be resolved by spreading out the calcium dose throughout the day, taking the supplement with meals, or changing the brand of supplement used.

Medicines

Because of its ability to neutralize stomach acid, calcium carbonate is found in some over-the-counter antacid products, such as Tums® and Rolaids®. Depending on its strength, each chewable pill or softchew provides 200 to 400 mg of calcium. As noted above, calcium carbonate is an acceptable form of supplemental calcium, especially for individuals who have normal levels of stomach acid.

Many Americans do not ingest recommended amounts of calcium from food. Approximately 44% of boys and 58% of girls aged 6-11 fell short in 1994-1996, as did 64% of boys and 87% of girls aged 12-19 years and 55% of men and 78% of women aged 20 years or older, according to the nationwide Continuing Survey of Food Intakes of Individuals. The National Health and Nutrition Examination Survey 1999-2000 found that average calcium intakes were 1,081 and 793 mg/day for boys and girls ages 12-19 years, respectively; 1,025 and 797 mg/day for men and women 20-39 years; and 797 and 660 mg/day for men and women ?60 years. Overall, females are less likely than males to get recommended intakes of calcium from food.

Not all calcium consumed is actually absorbed in the gut. Among the factors that affect its absorption are the following:

• Amount consumed: the efficiency of absorption decreases as the amount of calcium consumed at a meal increases.
• Age: 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 and continues to decrease as people age; this explains the higher recommended calcium intakes for ages ?51 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. In contrast, wheat products (with the exception of wheat bran) do not appear to have a negative impact on 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 take absorption into account.

Some absorbed calcium is eliminated from the body in urine, feces, and sweat. This amount is affected by such factors as the following:

• Sodium, potassium, and protein intakes: high intakes of sodium and protein increase calcium excretion. Adding more potassium to a high-sodium diet might help decrease calcium excretion, particularly in postmenopausal women.
• 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 2-3 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: these foods, when metabolized, shift the acid/base balance of the body towards the alkaline by producing bicarbonate, which reduces calcium loss. Metabolic acids produced by diets high in protein and cereal grains, for example, cause bone to release minerals such as calcium and phosphates and alkaline salts that neutralize the excess acid. In one experiment, women ?50 years of age who took supplements of bicarbonate showed significant reductions in calcium excretion, indicating reduced bone resorption.

Inadequate intakes of dietary calcium from food and supplements produce no obvious symptoms in the short term. Circulating blood levels of the nutrient, for example, 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.

Although frank calcium deficiency is uncommon, dietary intakes of the nutrient below recommended levels might have health consequences over the long term. The following groups are among those most likely to need extra calcium.

Postmenopausal women

Menopause leads to bone loss because decreases in estrogen production both increase bone resorption and decrease calcium absorption. Annual decreases in bone mass of 3%-5% per year frequently occur in the first years of menopause, but the decreases are typically less than 1% per year after age 65. Increased calcium intakes during menopause do not completely offset this bone loss.

Hormone replacement therapy (HRT) with estrogen and progesterone helps increase calcium levels and prevent osteoporosis and fractures. Estrogen therapy restores postmenopausal bone remodeling to the same levels as at premenopause, leading to lower rates of bone loss, perhaps in part by increasing calcium absorption in the gut. However, because of the potential health risks associated with HRT use, several medical groups and professional societies recommend that postmenopausal women consider using medications, such as bisphosphonates, instead of HRT to prevent or treat osteoporosis. In addition, consuming adequate amounts of calcium in the diet might help slow the rate of bone loss in all women.

Amenorrheic women and the female athlete triad

Amenorrhea, the condition in which menstrual periods stop or fail to initiate in women of childbearing age, results from reduced circulating estrogen levels that, in turn, have a negative effect on calcium balance. Amenorrheic women with anorexia nervosa have decreased calcium absorption and higher urinary calcium excretion rates, as well as a lower rate of bone formation than healthy women.

The “female athlete triad” refers to the combination of disordered eating, amenorrhea, and osteoporosis. Exercise-induced amenorrhea results in decreased bone mass. In female athletes and active women in the military, low bone-mineral density, menstrual irregularities, certain dietary patterns, and a history of prior stress factors are associated with an increased risk of future stress fractures. Such women should consume adequate amounts of calcium.

Individuals with lactose intolerance

Lactose intolerance refers to symptoms (such as bloating, flatulence, and diarrhea) that occur when one consumes more lactose, the naturally occurring sugar in milk, than the enzyme lactase produced by the small intestine can hydrolyze into its component monosaccharides, glucose and galactose. The symptoms vary, depending on the amount of lactose consumed, history of consumption of lactose-containing foods, and type of meal. Approximately 25% of U.S. adults have a limited ability to digest lactose, including 85% of Asians, 50% of African Americans, and 10% of Caucasians. Lactose-intolerant individuals are at risk of calcium inadequacy if they avoid dairy products.

Depending on the degree of lactose intolerance, some people with this condition might be able to consume moderate amounts of lactose, such as that present in 8 ounces of milk or in two 8-ounce glasses taken at different meals. Other options to reduce symptoms include drinking milk with a meal, inducing some adaptation by regularly eating foods with lactose daily for 2-3 weeks, or eating aged cheeses (such as Cheddar and Swiss with little lactose), yogurt (whose live active cultures aid in lactose digestion), or lactose-reduced or lactose-free milk. To ensure adequate calcium intakes, lactose-intolerant individuals can also choose nondairy food sources of the nutrient or take a calcium supplement.

Vegetarians

Vegetarians might absorb less calcium than omnivores because they consume more plant products containing oxalic and phytic acids. On the other hand, some vegetarian diets contain less protein than typical omnivore diets, which reduces calcium excretion. Lacto-ovo vegetarians (who consume eggs and dairy) and nonvegetarians have similar calcium intakes. However, vegans, who eat no animal products, might not obtain sufficient calcium because of their avoidance of dairy foods. It is difficult to assess the impact of vegetarian diets on calcium status because of the wide variety of eating practices.

Many claims are made about calcium’s potential benefits in health promotion and disease prevention and treatment. This section focuses on several areas in which calcium is or might be involved: bone health and osteoporosis; blood pressure regulation and hypertension; cancers of the colon, rectum, and prostate; kidney stones; and weight management.

Bone health and osteoporosis

Bones increase in size and mass during childhood and adolescence, reaching peak bone mass around age 30. The greater the peak bone mass, the longer one can delay serious bone loss with increasing age. Everyone should therefore consume adequate amounts of calcium and vitamin D throughout childhood, adolescence, and early adulthood.

Osteoporosis, a disorder characterized by porous and fragile bones, is a serious public health problem for more than 10 million U.S. adults, 80% of whom are women. (Another 34 million have osteopenia, or low bone mass, which precedes osteoporosis.) Osteoporosis is associated with fractures of the hip, vertebrae, wrist, pelvis, ribs, and other bones. An estimated 1.5 million fractures occur each year in the United States due to osteoporosis.

When calcium intake is low or ingested calcium is poorly absorbed, bone breakdown occurs as the body uses its stored calcium to maintain normal biological functions. Bone loss also occurs as part of the normal aging process, particularly in postmenopausal women due to decreased amounts of estrogen. Many factors increase the risk of developing osteoporosis, including being female, thin, inactive, or of advanced age; smoking cigarettes; drinking excessive amounts of alcohol; and having a family history of osteoporosis.

Various bone mineral density (BMD) tests are available. The T-score from these tests compares an individual’s BMD to an optimal BMD (that of a healthy 30-year old adult). A T-score between +1 and -1 indicates normal bone density, -1.0 to -2.5 indicates low bone mass (osteopenia), and lower than -2.5 osteoporosis.

Although osteoporosis affects individuals of all races, ethnicities, and both genders, women are at highest risk because their skeletons are smaller than those of men and because of the accelerated bone loss that accompanies menopause. Adequate intakes of calcium and vitamin D as well as regular exercise (both weight-bearing such as walking, running, and activities where one’s feet leave and hit the ground and work against gravity, as well as resistance exercises such as calisthenics and that involve weights) are critical to the development and maintenance of healthy bones throughout the life cycle.

In 1993, the U.S. Food and Drug Administration authorized a health claim related to calcium and osteoporosis for foods and supplements. In January 2010, this health claim is expanded to include vitamin D. Model health claims include the following: “Adequate calcium throughout life, as part of a well-balanced diet, may reduce the risk of osteoporosis” and “Adequate calcium and vitamin D as part of a healthful diet, along with physical activity, may reduce the risk of osteoporosis in later life”.

Blood pressure and hypertension

Several clinical trials have demonstrated a relationship between increased calcium intakes and both lower blood pressure and risk of hypertension, although the reductions are inconsistent. The authors of a systematic review of the effects of calcium supplements for hypertension found any link to be weak at best, largely due to the poor quality of most studies and differences in methodologies. Other observational and experimental studies suggest that individuals who eat a vegetarian diet high in minerals (such as calcium, magnesium, and potassium) and fiber and low in fat tend to have lower blood pressure.

The Dietary Approaches to Stop Hypertension (DASH) study was conducted to test the effects of three different eating patterns on blood pressure: a control “typical” American diet; one high in fruits and vegetables; and a third diet high in fruits, vegetables, and low-fat dairy products. The diet containing dairy products resulted in the greatest decrease in blood pressure, although the contribution of calcium to this effect was not evaluated.

Cancer of the colon and rectum

Observational and experimental studies on the potential role of calcium in preventing colorectal cancer provide mixed results. Several studies have found that higher intakes of calcium from foods (low-fat dairy sources) and/or supplements are associated with a decreased risk of colon cancer.

Supplementation with calcium carbonate has led to reductions in the risk of adenoma (a nonmalignant tumor) in the colon, a precursor to cancer, even as long as 5 years after the person stopped taking the supplement. In two large prospective epidemiological trials, men and women who consumed 700-800 mg per day of calcium had a 40%-50% lower risk of developing left-side colon cancer.

But other observational studies have found the associations to be inconclusive. In the Women’s Health Initiative, a clinical trial involving 36,282 postmenopausal women, daily supplementation with 1,000 mg of calcium and 400 IU of vitamin D₃ for 7 years produced no significant differences in the risk of invasive colorectal cancer compared to placebo. Given the long latency period for colon cancer development, long-term studies are needed to understand whether calcium intakes affect colorectal cancer risk.

Cancer of the prostate

Several epidemiological studies have found an association between calcium intakes of 600 mg or more per day, intakes of more than 2.5 servings of dairy foods, or both and an increased risk of developing prostate cancer. However, others have found only a weak relationship, no relationship, or a negative association between calcium intake and prostate cancer risk. The authors of a meta-analysis of prospective studies concluded that high intakes of dairy products and calcium might slightly increase prostate cancer risk. Additional research is needed to determine whether a man’s risk of prostate cancer is affected by the amount of dairy products or calcium consumed.

Kidney stones

Kidney stones in the urinary tract are most commonly composed of calcium oxalate. In the Women’s Health Initiative clinical trial, postmenopausal women who consumed 1,000 mg of supplemental calcium and 400 IU of vitamin D per day for 7 years had a higher risk of kidney stones than subjects taking a placebo. Other studies, however, have found that high dietary calcium intakes decrease this risk. For most individuals, other risk factors for kidney stones, such as high intakes of oxalates from food and low intakes of fluid, appear to play a bigger role than calcium.

Weight management

Several studies have linked higher calcium intakes to lower body weight or less weight gain over time. Two explanations have been proposed. First, high calcium intakes might reduce calcium concentrations in fat cells by decreasing the production of two hormones (parathyroid hormone and an active form of vitamin D) that increase fat breakdown in these cells and discourage fat accumulation. Secondly, calcium from food or supplements might bind to small amounts of dietary fat in the digestive tract and prevent its absorption. Dairy products, in particular, might contain additional components that have even greater effects on body weight than their calcium content alone would suggest.

Despite these findings, the results from clinical trials have been largely negative. For example, a meta-analysis of 13 randomized controlled trials concluded that neither calcium supplementation nor increased dairy product consumption has a statistically significant effect on weight reduction. A more recent clinical trial found dietary supplementation with 1,500 mg/day of calcium (from calcium carbonate) for 2 years to have no clinically significant effects on weight in overweight and obese adults as compared with placebo. Any apparent effects of calcium and dairy products on weight regulation and body composition are complex, inconsistent, and not well understood.

Excessively high levels of calcium in the blood known as hypercalcemia impair kidney function, and lead to reduced absorption of other essential minerals, such as iron, zinc, magnesium, and phosphorus. However, hypercalcemia rarely results from dietary or supplemental calcium intake and is most commonly associated with hyperparathyroidism, advanced cases of cancer or excessive intakes of vitamin D from supplements at doses of 50,000 IU/day or higher. The Tolerable Upper Intake Levels (ULs) for calcium established by the Food and Nutrition Board are listed in Table 3.

Table 3: Tolerable Upper Intake Levels (ULs) for Calcium

Age	Male	Female	Pregnant	Lactating
Birth to 12 months	None established	None established
1-13 years	2,500 mg	2,500 mg
14-50 years	2,500 mg	2,500 mg	2,500 mg	2,500 mg
51+ years	2,500 mg	2,500 mg

mg = milligrams

Calcium supplements have the potential to interact with several types of medications. This section provides a few examples. Individuals taking these medications on a regular basis should discuss their calcium intake with their healthcare providers.

Calcium can decrease the absorption of the following drugs when taken together: biphosphonates (to treat osteoporosis), the fluoroquinolone and tetracycline classes of antibiotics, levothyroxine, phenytoin (an anticonvulsant), and tiludronate disodium (to treat Paget’s disease).

Thiazide-type diuretics can interact with calcium carbonate and vitamin D supplements, increasing the risks of hypercalcemia and hypercalciuria. Both aluminum- and magnesium-containing antacids increase urinary calcium excretion. Mineral oil and stimulant laxatives decrease calcium absorption. Glucocorticoids, such as prednisone, can cause calcium depletion and eventually osteoporosis when they are used for months.

According to the 2005 Dietary Guidelines for Americans, “nutrient needs should be met primarily through consuming foods. Foods provide an array of nutrients and other compounds that may have beneficial effects on health. In certain cases, fortified foods and dietary supplements may be useful sources of one or more nutrients that otherwise might be consumed in less than recommended amounts. However, dietary supplements, while recommended in some cases, cannot replace a healthful diet.”

The Dietary Guidelines for Americans describe a healthy diet as one that: