What is calcium?
Calcium is a mineral your body needs to help build strong bones and healthy teeth. Low-fat and fat-free milk and dairy products are especially good sources of calcium.
Calcium, the most abundant mineral in the human body, has several important functions. More than 99% of total body calcium is stored in the bones and teeth where it functions to support their structure. The remaining 1% is found throughout the body in blood, muscle, and the fluid between cells. Calcium is needed for muscle contraction, blood vessel contraction and expansion, the secretion of hormones and enzymes, and sending messages through the nervous system. A constant level of calcium is maintained in body fluid and tissues so that these vital body processes function efficiently.
Bone undergoes continuous remodeling, with constant resorption (breakdown of bone) and deposition of calcium into newly deposited bone (bone formation). The balance between bone resorption and deposition changes as people age. During childhood there is a higher amount of bone formation and less breakdown. In early and middle adulthood, these processes are relatively equal. In aging adults, particularly among postmenopausal women, bone breakdown exceeds its formation, resulting in bone loss, which increases the risk for osteoporosis (a disorder characterized by porous, weak bones).
Why is calcium important for strong bones and teeth?
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.
Recommended Adequate Intake
|Male and Female Age
||Pregnancy & Lactation
| 0 to 6 months
| 7 to 12 months
| 1 to 3 years
| 4 to 8 years
| 9 to 13 years
| 14 to 18 years
| 19 to 50 years
| 51+ years
Good sources of calcium
Calcium is found in a variety of foods. Low-fat and fat-free milk and other dairy products are great sources of calcium because of they have so much of it.
Tweens and teens can get most of their daily calcium from 3 cups of low-fat or fat-free milk, but they also need additional servings of calcium to get the 1,300 mg necessary for strong bones.
Other reasons low-fat and fat-free milk and dairy products are great sources of calcium include:
Low-fat and fat-free milk has lots of calcium with little or no fat.
The calcium in low-fat and fat-free milk and dairy products is easy for the body to absorb and in a form that gives the body easy access to the calcium.
Low-fat and fat-free milk has added vitamin D, which is important for helping your body better absorb calcium.
In addition to calcium, milk and dairy products provide other essential nutrients that are important for optimal bone health and development.
In addition to low-fat and fat-free milk and dairy products, there are other good sources of calcium, including:
Dark green, leafy vegetables, such as spinach, broccoli, and bok choy.
Foods with calcium added, such as calcium-fortified tofu, orange juice, soy beverages, and breakfast cereals or breads.
Selected Food Sources of Calcium
| Yogurt, plain, low fat, 8 oz.
| Yogurt, fruit, low fat, 8 oz.s
| Sardines, canned in oil, with bones, 3 oz.
| Cheddar cheese, 1 ˝ oz shredded
| Milk, non-fat, 8 fl oz.
| Milk, reduced fat (2% milk fat), no solids, 8 fl oz.
| Milk, whole (3.25% milk fat), 8 fl oz
| Milk, buttermilk, 8 fl oz.
| Milk, lactose reduced, 8 fl oz.**
| Mozzarella, part skim 1 ˝ oz..
| Tofu, firm, made w/calcium sulfate, ˝ cup***
| Orange juice, calcium fortified, 6 fl oz.
| Salmon, pink, canned, solids with bone, 3 oz.
| Pudding, chocolate, instant, made w/ 2% milk, ˝ cup
| Cottage cheese, 1% milk fat, 1 cup unpacked
| Tofu, soft, made w/calcium sulfate, ˝ cup***
| Spinach, cooked, ˝ cup
| Instant breakfast drink, various flavors and brands,
powder prepared with water, 8 fl oz.
| Frozen yogurt, vanilla, soft serve, ˝ cup
| Ready to eat cereal, calcium fortified, 1 cup
| Turnip greens, boiled, ˝ cup
| Kale, cooked, 1 cup
| Ice cream, vanilla, ˝ cup
| Soy beverage, calcium fortified, 8 fl oz.
| Chinese cabbage, raw, 1 cup
| Tortilla, corn, ready to bake/fry, 1 medium
| Tortilla, flour, ready to bake/fry, one 6" diameter
| Sour cream, reduced fat, cultured, 2 Tbsp
| Bread, white, 1 oz
| Broccoli, raw, ˝ cup
| Bread, whole wheat, 1 slice
| Cheese, cream, regular, 1 Tbsp
**Content varies slightly according to fat content; average =300 mg calcium
*** Calcium values are only for tofu processed with a calcium salt. Tofu processed with a non-calcium salt will not contain significant amounts of calcium.
Daily Values (DV) were developed to help consumers determine if a typical serving of a food contains a lot or a little of a specific nutrient. The DV for calcium is based on 1000 mg.
Factors which affects calcium absorption and excretion
Calcium absorption refers to the amount of calcium that is absorbed from the digestive tract into our body's circulation. Calcium absorption can be affected by the calcium status of the body, vitamin D status, age, pregnancy and plant substances in the diet. The amount of calcium consumed at one time such as in a meal can also affect absorption. For example, the efficiency of calcium absorption decreases as the amount of calcium consumed at a meal increases.
Net calcium absorption can be as high as 60% in infants and young children, when the body needs calcium to build strong bones. Absorption slowly decreases to 15-20% in adulthood and even more as one ages. Because calcium absorption declines with age, recommendations for dietary intake of calcium are higher for adults ages 51 and over.
Vitamin D helps improve calcium absorption. Your body can obtain vitamin D from food and it can also make vitamin D when your skin is exposed to sunlight. Thus, adequate vitamin D intake from food and sun exposure is essential to bone health.
Current calcium recommendations for non pregnant women are also sufficient for pregnant women because intestinal calcium absorption increases during pregnancy. For this reason, the calcium recommendations established for pregnant women are not different than the recommendations for women who are not pregnant.
Phytic acid and oxalic acid, which are found naturally in some plants, may bind to calcium and prevent it from being absorbed optimally. These substances affect the absorption of calcium from the plant itself not the calcium found in other calcium-containing foods eaten at the same time. Examples of foods high in oxalic acid are spinach, collard greens, sweet potatoes, rhubarb, and beans. Foods high in phytic acid include whole grain bread, beans, seeds, nuts, grains, and soy isolates. Although soybeans are high in phytic acid, the calcium present in soybeans is still partially absorbed. Fiber, particularly from wheat bran, could also prevent calcium absorption because of its content of phytate. However, the effect of fiber on calcium absorption is more of a concern for individuals with low calcium intakes.
Calcium excretion refers to the amount of calcium eliminated from the body in urine, feces and sweat. Calcium excretion can be affected by many factors including dietary sodium, protein, caffeine and potassium.
Sodium and protein
Typically, dietary sodium and protein increase calcium excretion as the amount of their intake is increased. However, if a high protein, high sodium food also contains calcium, this may help counteract the loss of calcium.
Increasing dietary potassium intake (such as from 7-8 servings of fruits and vegetables per day) in the presence of a high sodium diet (>5100 mg/day, which is more than twice the Tolerable Upper Intake Level of 2300 mg for sodium per day) may help decrease calcium excretion particularly in postmenopausal women.
Caffeine has a small effect on calcium absorption. It can temporarily increase calcium excretion and may modestly decrease calcium absorption, an effect easily offset by increasing calcium consumption in the diet. One cup of regular brewed coffee causes a loss of only 2-3 mg of calcium easily offset by adding a tablespoon of milk. Moderate caffeine consumption, (1 cup of coffee or 2 cups of tea per day), in young women who have adequate calcium intakes has little to no negative effects on their bones.
: The effect of dietary phosphorus on calcium is minimal. Some researchers speculate that the detrimental effects of consuming foods high in phosphate such as carbonated soft drinks is due to the replacement of milk with soda rather than the phosphate level itself.
: Alcohol can affect calcium status by reducing the intestinal absorption of calcium. It can also inhibit enzymes in the liver that help convert vitamin D to its active form which in turn reduces calcium absorption. However, the amount of alcohol required to affect calcium absorption is unknown. Evidence is currently conflicting whether moderate alcohol consumption is helpful or harmful to bone.
Calcium's role in health and disease prevention
Calcium and bone health
The bones are living tissues and continue to change throughout life. During childhood and adolescence, bones increase in size and mass. Bones continue to add more mass until around age 30, when peak bone mass is reached. Peak bone mass is the point when the maximum amount of bone is achieved. Because bone loss, like bone growth, is a gradual process, the stronger your bones are at age 30, the more your bone loss will be delayed as you age. Therefore, it is particularly important to consume adequate calcium and vitamin D throughout infancy, childhood, and adolescence.
Osteoporosis is a disorder characterized by porous, fragile bones. Osteoporosis is a concern because of its association with fractures of the hip, vertebrae, wrist, pelvis, ribs, and other bones. Each year, Americans suffer from 1.5 million fractures because of osteoporosis.
Osteoporosis and osteopenia can result from dietary factors such as:
- chronically low calcium intake
- low vitamin D intake
- poor calcium absorption
- excess calcium excretion
When calcium intake is low or calcium is poorly absorbed, bone breakdown occurs because the body must use the calcium stored in bones to maintain normal biological functions such as nerve and muscle function. Bone loss also occurs as a part of the aging process.
Researchers have identified many factors that increase the risk for developing osteoporosis. These factors include being female, thin, inactive, of advanced age, cigarette smoking, excessive intake of alcohol, and having a family history of osteoporosis.
Although osteoporosis affects people of different races, genders and ethnicities, women are at highest risk because their skeletons are smaller to start with and because of the accelerated bone loss that accompanies menopause. Adequate calcium and vitamin D intakes, as well as weight bearing exercise are critical to the development and maintenance of healthy bone throughout the lifecycle. Older adults should strive to maintain recommended daily calcium intakes as well as an adequate vitamin D intake.
Calcium and high blood pressure
Some observational studies and experimental studies indicate that individuals who eat a vegetarian diet high in minerals (including calcium, magnesium and potassium) and fiber, and low in fat, tend to have reduced blood pressure.
Findings from some clinical trials (a specific type of experimental study) used to evaluate the effects of one or more treatments/interventions in humans) indicate that an increased calcium intake lowers blood pressure and the risk of hypertension (high blood pressure).
Calcium and cancer
The relationship between calcium intake and the risk of colon cancer has not been conclusively determined. Observational and experimental research studies investigating the role calcium plays in the prevention of colon cancer show mixed results. Some studies suggest that increased intakes of dietary (low fat dairy sources) and supplemental calcium are associated with a decreased risk of colon cancer. Supplementation with calcium carbonate is reported to lead to reduced risk of adenomas (nonmalignant tumors) in the colon, a precursor to colon cancer, but it is not known if this will ultimately translate into reduced cancer risk.
There is some evidence to suggest that higher calcium (ranging from 600 mg to >2000 mg of calcium) and/or dairy intakes (>2.5 servings) may be associated with the development of prostate cancer. However, these studies are observational in nature rather than clinical trials and cannot establish a definite causal relationship between calcium and prostate cancer. Other findings only show a weak relationship, no relationship at all or the opposite relationship between calcium and prostate cancer. Thus, the relationship between calcium intake, dairy intake and prostate cancer risk remains unclear.
Calcium and kidney stones
Kidney stones are crystallized deposits of calcium and other minerals in the urinary tract. Calcium oxalate stones are the most common form of kidney stones. High calcium intakes or high calcium absorption were previously thought to contribute to the development of kidney stones. However, more recent studies show that high dietary calcium intakes actually decrease the risk for kidney stones. Other factors such as high oxalate intake and reduced fluid consumption appear to be more of a risk factor in the formation of kidney stones than calcium in most individuals.
Calcium and weight management
Several studies, primarily observational in nature, have linked higher calcium intakes to lower body weights or less weight gain over time. High-calcium intakes may reduce calcium concentrations in fat cells by lowering the production of two hormones (parathyroid hormone and an active form of vitamin D), which in turn increases fat breakdown in these cells and discourages its accumulation. In addition, calcium from food or supplements may bind to small amounts of dietary fat in the digestive tract and prevent its absorption, carrying the fat (and the calories it would otherwise provide) out in the feces.
Inadequate calcium intake, decreased calcium absorption, and increased calcium loss in urine can decrease total calcium in the body, with the potential of producing osteoporosis and the other consequences of chronically low calcium intake. If an individual does not consume enough dietary calcium or experiences rapid losses of calcium from the body, calcium is withdrawn from their bones in order to maintain calcium levels in the blood.
Signs of calcium deficiency
Because circulating blood calcium levels are tightly regulated in the bloodstream, hypocalcemia (low blood calcium) does not usually occur due to low calcium intake, but rather results from a medical problem or treatment such as renal failure, surgical removal of the stomach (which significantly decreases calcium absorption), and use of certain types of diuretics (which result in increased loss of calcium and fluid through urine). Simple dietary calcium deficiency produces no signs at all. Hypocalcemia can cause numbness and tingling in fingers, muscle cramps, convulsions, lethargy, poor appetite, and mental confusion. It can also result in abnormal heart rhythms and even death. Individuals with medical problems that result in hypocalcemia should be under a medical doctor's care and receive specific treatment aimed at normalizing calcium levels in the blood.
Who may need extra calcium to prevent a deficiency?
Menopause often leads to increases in bone loss with the most rapid rates of bone loss occurring during the first five years after menopause. Drops in estrogen production after menopause result in increased bone resorption, and decreased calcium absorption. Annual decreases in bone mass of 3-5% per year are often seen during the years immediately following menopause, with decreases less than 1% per year seen after age 65.
Hormone therapy (HT), previously known as hormone replacement therapy (HRT), with sex hormones such as estrogen and progesterone, helps to prevent osteoporosis and fractures. Postmenopausal women using combination HT to reduce bone loss should consult with their physician about the risks and benefits of estrogen therapy for their health.
Estrogen therapy works to restore postmenopausal bone remodeling levels back to those of premenopause, leading to a lower rate of bone loss. Estrogen appears to interact with supplemental calcium by increasing calcium absorption in the gut. However, including adequate amounts of calcium in the diet may help slow the rate of bone loss for all women.
Amenorrheic Women and the Female Athlete Triad
Amenorrhea is the condition when menstrual periods stop or fail to initiate in women who are of childbearing age. Secondary amenorrhea is the absence of three or more consecutive menstrual cycles after menarche occurs (first menstrual period). The secondary type of amenorrhea can be induced by exercise in athletes and is referred to as "athletic amenorrhea". Potential causes of athletic amenorrhea include low body weight and low percent body fat, rapid weight loss, sudden onset of vigorous exercise, disordered eating and stress. Amenorrhea results from decreases in circulating estrogen, which then negatively affect calcium balance. Studies comparing healthy women with normal menstrual cycles to amenorrheic women with anorexia nervosa (a type of disordered eating) found decreased levels of calcium absorption, a higher urinary calcium excretion, and a lower rate of bone formation in women with anorexia.
The condition "female athlete triad" refers to the combination of disordered eating, amenorrhea, and osteoporosis. Exercise-induced amenorrhea has been shown to result in decreases in bone mass.
Lactose Intolerant Individuals
Lactose maldigestion (or "lactase non-persistence") describes the inability of an individual to completely digest lactose, the naturally occurring sugar in milk. Lactose intolerance refers to the symptoms that occur when the amount of lactose exceeds the ability of an individual's digestive tract to break down lactose.
Symptoms of lactose intolerance include bloating, flatulence, and diarrhea after consuming large amounts of lactose (such as the amount in 1 quart of milk). Lactose maldigesters may be at risk for calcium deficiency, not due to an inability to absorb calcium, but rather from the avoidance of dairy products. Although some lactose maldigesters avoid dairy products, others are able to consume moderate amounts of lactose, such as the amount in an 8-oz glass of milk. Some individuals may be able to consume two 8-oz glasses of milk a day if they do so at different meals.
Drinking milk with a meal helps reduce symptoms of lactose intolerance substantially. In addition, regularly eating foods (e.g. daily for 2-3 weeks) with lactose (such as milk) can help the body adapt to the lactose and thus reduce symptoms of lactose intolerance.
There are several types of vegetarian eating practices. Individuals may choose to include some animal products (ovo-vegetarian, lacto-vegetarian, lacto-ovo vegetarian, pesco-vegetarian) or no animal products (vegan) in their diet. Calcium intakes between lacto-ovo-vegetarians (those who consume eggs and dairy products) and non-vegetarians have been shown to be similar.
Calcium absorption may be reduced in vegetarians because they eat more plant foods containing oxalic and phytic acids, compounds which interfere with calcium absorption. However, vegetarian diets that contain less protein may reduce calcium excretion. Therefore, it is important for vegans to include adequate amounts of non-dairy sources of calcium in their daily diet or consider taking a calcium supplement to meet their recommended calcium intake. Furthermore, while early studies found vegetarian diets to be beneficial for bone health, more recent studies have found no benefits or even the opposite effect.