Osteoporosis and Calcium

Osteoporosis and Calcium Definitions and Facts

Illustration of bones affected by osteoporosis.
The amount of calcium needed daily depends on a person's age and gender.

Calcium is an important nutrient and is needed for many of the body's functions, including blood clotting and the proper function of the heart, muscles, and nerves. Calcium is also critical for the health and strength of bones. Not getting enough calcium can contribute to the development of osteoporosis (porous bones).

Osteoporosis is a disease characterized by bones that are thin and fragile and can break (fracture) easily. People with osteoporosis have low bone mass, and low bone mass can result in bone fractures.

Having enough calcium intake in the diet is essential in helping to prevent osteoporosis and helping to prevent the loss of bone mass.

Calcium alone cannot protect a person from bone loss caused by certain medications or diseases, smoking, alcoholism, not enough exercise, or a lack of estrogen. Calcium does help a person maintain healthy bones, though, and it helps children and adolescents grow strong bones. However, only 50%-60% of adults and only 10%-25% of adolescents in the United States get the recommended amount of calcium.

Calcium and Bone Mass

Bones may seem like hard and lifeless structures, but they are, in fact, living tissue. Old bone is constantly broken down (through a process called resorption) by our bodies, and new bone is deposited. Anytime bone is broken down faster than it is deposited, bone weakness and osteoporosis can occur.

Bones are made from collagen and non-collagen proteins, and they are fortified with calcium. If a person does not take in enough calcium from their diet, the body extracts calcium from the bones, resulting in loss of bone strength and mass. This can ultimately lead to thin, fragile bones and osteoporosis.

More than 90% of a person's bone mass develops before 20 years of age, and half of that bone mass develops from 11-15 years of age. To have strong bones, children and adolescents need to consume enough calcium to build up the bone mass that they will need throughout their lives.

Even after age 20, a person can help protect his or her bones. Bone mass can still be built up until the early 30s. After that, protecting the amount of bone that already exists comes from consuming enough calcium because calcium is essential in maintaining bone mass.

Calcium works like this:

  • After calcium is consumed, several nutrients, especially vitamin D, help the body absorb the calcium.
  • The blood transports the calcium that is not needed for other body processes to the bones where it adds to the bone mass and is stored for when it is needed in the rest of the body.
  • Sometimes a lack of calcium comes from not consuming enough in the diet or because the body is not absorbing enough into the blood. When this happens, calcium is removed from the bones into the blood to keep a constant level of calcium in the blood.

Adequate calcium intake is important to keep a normal amount of calcium in the blood and to protect the bones from calcium loss. If enough calcium is not regularly consumed and the calcium continues to be taken from the bones, a person's bone mass decreases. Decreased bone mass can lead to osteoporosis, fractures, and disability.

Adequate calcium intake is also important because the body cannot produce calcium on its own. Every day, the body loses calcium through shedding hair, skin, and nails and through sweat, urine, and feces. Every day, this lost calcium must be replaced by what a person eats.

How Does Calcium Help Prevent Osteoporosis?

Calcium makes bones strong. In fact, bones and teeth contain 99% of the body's total calcium, with the remaining 1% in intracellular and extracellular fluids. Bones act as a storehouse for calcium, which is used by the body and replaced by the diet throughout a person's life. If enough calcium is not consumed, the body takes it from the bones. If more calcium is removed from the bones than is consumed in the diet, the bones become fragile and weak as a person gets older, leading to osteoporosis and fractures.

Osteoporosis prevention begins during childhood and adolescence by getting enough exercise and the proper nutrients, including calcium and vitamin D. However, adults can help prevent osteoporosis in the same ways.

The importance of calcium in developing and maintaining bone mass (bone density) varies throughout a person's life. At times of rapid and significant bone growth (during the teenage years) or rapid bone loss (after age 50 years), calcium is more important. Therefore, to reduce the risk of osteoporosis, calcium intake should be the highest during adolescence and after 50 years of age. See Prevention of Osteoporosis for more information.

How Much Calcium Is Needed?

Since the body's calcium needs change with age, calcium intake should be adjusted as necessary. Depending on age, an appropriate calcium intake is generally between 1,000 and 1,300 milligrams (mg) a day.

The amount of calcium needed daily depends on a person's age and gender.

After extensive consideration, the United States Institute of Medicine decided on the following recommendations for calcium intake. These recommendations were issued in a report in November 2010. These recommendations indicate the total amount of calcium from food and supplements combined.

Calcium Recommended Daily Allowances
Age Range (Years) Calcium (mg/Day)
9-18 1,300
51-70 (Men)
51-70 (Women) 1,200
Over 70 1,200

The intestines can only absorb about 500-600 mg of calcium at a time, and so total calcium intake should be divided over the course of a day. Taking too much calcium can lead to kidney stone formation. Excess calcium intake may be associated with other health risks, including heart attacks and strokes, but the scientific studies are not conclusive. Therefore, when it comes to calcium intake, it is important to get enough calcium, however, more is not better.

What Foods Contain Calcium?

Dairy foods generally contain the most concentrated amounts of calcium. The calcium is not contained in the "fat portion" of dairy products, so removing the fat (as in low-fat dairy foods) does not affect the calcium content. In fact, many low-fat dairy foods are made by replacing the fat portion with an equal part of skimmed milk, so these foods actually have increased calcium content. In other words, 1 cup of skim or low-fat milk has more calcium than 1 cup of whole milk because almost the entire cup of skim milk is made up of the calcium-containing portion.

Although dairy foods generally contain the most concentrated amounts of calcium, many other foods are good sources of calcium. Here are some food ideas and the amount of calcium they contain:

Dairy foods

  • 1 cup of milk - 291-302 mg
  • 1 cup of yogurt - 345-415 mg
  • 1 ounce of American cheese - 174 mg
  • 1 ounce of cheddar cheese - 191 mg
  • 1 ounce of mozzarella cheese - 207 mg
  • ½ cup ricotta cheese - 337 mg
  • 1 cup of fortified soy or rice beverage - 250 mg-300 mg
  • ½ cup ice cream - 80 mg-90 mg

Protein foods

  • 1 cup beans (cooked) - 90 mg
  • ½ cup soybeans (cooked) - 130 mg
  • ½ cup tofu - 204 mg
  • ½ cup hummus - 66 mg
  • 3 ounces canned salmon (with bones) - 167 mg
  • 3 ounces canned sardines (with bones) - 371 mg
  • 4 ounces salmon - 300 mg
  • ½ cup almonds - 188 mg
  • 1 tablespoon sesame seeds - 88 mg


  • 1 cup calcium-fortified orange juice - 300 mg
  • 1 orange - 92 mg
  • ½ cup dried figs - 144 mg
  • ½ cup rhubarb - 174 mg


  • ½ cup broccoli (cooked) - 89 mg
  • ½ cup kale (cooked) -90 mg
  • ½ cup collard greens (cooked) - 74 mg
  • ½ cup spinach (cooked) - 61 mg


  • 1 cup fortified cereal - 200 mg-300 mg
  • 1 English muffin (wheat) - 175 mg
  • 2 slices bread (white) - 70 mg

The enzyme lactase can help people who are lactose intolerant digest dairy products. It can be taken either as a pill or in liquid form. Some dairy products in stores have lactase already added, other products are lactose free.

What Impairs the Absorption of Calcium?

Some things impair absorption of calcium, so more calcium must be ingested in the diet to make up for what is not being absorbed.

  • Corticosteroids: Corticosteroid therapy, such as prednisone, taken for longer than six weeks, an extra 300-500 milligrams of calcium should be consumed a day (or a total of 1,500 milligrams daily).
  • Sodium: Sodium increases the amount of calcium that is excreted in the urine, so if eating foods high in salt, more calcium should be consumed.
  • Excess protein: The body uses excess protein for energy. However, as protein is burned for energy, it produces sulfate. Sulfate increases the amount of calcium excreted in the urine, which decreases the amount of calcium in the body. Excess protein creates excess sulfate.
  • Oxalate: Found in some foods and beverages, most notably spinach, chard, berries, chocolate, and tea, oxalate binds with calcium and increases the loss of calcium through fecal excretion. For example, even though sweet potatoes contain calcium, not all of it is absorbed because of the oxalic acid (oxalate) that is also in them.
  • Phosphorous: Also known as phosphoric acid and phosphate, phosphorous, which is in cola and many processed foods, can interfere with calcium absorption.
  • Insoluble fiber: This type of fiber, such as the kind in wheat bran, reduces calcium absorption.
  • Alcohol intake: Drinking excessive amounts of alcohol can interfere with the calcium balance by inhibiting the enzymes that convert inactive vitamin D to active vitamin D.
  • Caffeine: Excessive intake of caffeine (300 mg-400 mg) can increase urinary excretion as well as fecal excretion. (One cup [8 fl oz] of brewed coffee contains about 137 mg of caffeine.)
  • Smoking, stress, and lack of exercise: These lifestyle factors contribute to the body not being able to absorb calcium as efficiently.

What Assists the Absorption of Calcium?

Vitamin D is the most significant nutrient for the proper absorption of calcium. Vitamin D and calcium work together to slow down or even reverse osteoporosis. Vitamin D is essential in helping the body absorb and use calcium; in fact, the body cannot absorb calcium at all without some vitamin D.

Vitamin D comes from two sources. It is made in the skin through direct exposure to sunlight, and it comes from the diet. The body's ability to produce vitamin D from exposure to sunlight and to absorb calcium and vitamin D decreases with age. Getting enough vitamin D helps the body absorb calcium and also helps the kidneys break down and incorporate (resorb) calcium that would otherwise be excreted. Vitamin D is found in eggs, butter, fatty fish, liver, and fortified foods such as milk, orange juice, and cereal. Elderly individuals who are not exposed to sunlight and may not eat a variety of food containing vitamin D may need vitamin D supplements to maintain adequate levels to help calcium absorption.

In addition to vitamin D, vitamin C, vitamin E, vitamin K, magnesium, and boron assist in absorbing calcium and also increasing bone mass. Exercise also helps the body absorb calcium.

Because the body has a hard time absorbing a large amount of calcium at once, spreading out the intake of calcium is recommended. Taking in about 500 mg or less of calcium several times throughout the day is best.

Calcium Supplements

While experts recommend getting as much calcium and other nutrients as possible from foods instead of from supplements, it may be difficult to get all the calcium needed from diet alone. A calcium supplement may be taken to help make up the difference.

Calcium supplements come in a variety of different forms, including compounds such as calcium citrate (Citracal or Solgar), calcium lactate, and calcium gluconate. The actual amount of calcium, called elemental calcium, varies in each supplement. Chelated forms of calcium, such as in the compounds just listed, are more easily absorbed by the body than other forms of calcium. However, calcium carbonate (Os-Cal or Tums), while not as easily absorbed, contains the highest amount of elemental calcium.

Be sure to examine the labels of supplements to see how much elemental calcium they have and what the serving sizes are. In some cases, the serving size is more than one tablet.

Calcium carbonate and calcium citrate are the most commonly used calcium supplements, particularly because they contain more calcium per tablet and are less expensive per milligram of calcium than other supplements. Calcium carbonate supplies more elemental calcium per tablet than other forms and is therefore usually the best value; however, it is best to take this kind of calcium compound with food because stomach acid is needed to dissolve it. Calcium citrate has less elemental calcium in it, so more of it will need to be taken, but it is absorbed more easily than calcium carbonate.

When taking a supplement, a few other things should be considered.

  • More isn't always better; the recommended daily dose should not be exceeded because exceeding the dose increases the risk of side effects.
  • A doctor or pharmacist knows whether a calcium supplement will interact with any prescription medications also being taken. For example, calcium chews, such as Viactiv, contain calcium and vitamin D but also contain vitamin K and should not be taken by individuals treated with anticoagulants, such as warfarin (Coumadin).
  • To retain maximum supplement absorption, just as with dietary calcium, take only about 500 mg or less at one time.

When purchasing a calcium supplement, check with the pharmacist or doctor. Since the manufactures of these dietary supplements are not regulated as prescription medications, look for a reputable brand name or a company that advertises "quality control." This ensures that the advertised amount of elemental calcium per tablet is correct.

Treatment with Calcium

A diet that includes adequate calcium and vitamin D is essential. Recommendations for people with osteoporosis include a daily dosage of 1,200 mg of calcium along with 600-800 IU (international units) of vitamin D. A doctor can measure levels of calcium in the blood and urine, how much vitamin D is in the blood, and make suggestions to ensure that the correct dosages are taken.

Calcium may also boost the power of other osteoporosis treatments, such as hormone replacement therapy. Bone mass is significantly greater in women on hormone replacement therapy who consume more calcium.

What Does Osteoporosis Look Like?

The image on the left shows decreased bone density in osteoporosis. The image on the right shows normal bone density.
The image on the left shows decreased bone density in osteoporosis. The image on the right shows normal bone density.

Arrow indicates vertebral fractures.
Arrow indicates vertebral fractures.

A. Normal spine, B. Moderately osteoporotic spine, C. Severely osteoporotic spine.
A. Normal spine, B. Moderately osteoporotic spine, C. Severely osteoporotic spine.

For More Information About Osteoporosis and Calcium

National Osteoporosis Foundation
1232 22nd Street NW
Washington, DC 20037-1292

International Osteoporosis Foundation
[email protected]

National Institutes of Health Osteoporosis and Related Bone Diseases National Resource Center
2 AMS Circle
Bethesda, MD 20892-3676
[email protected]

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Foods That Help to Prevent Osteoporosis

Many foods can help prevent osteoporosis. A number of scientific studies have shown that eating more fruits and vegetables leads to stronger bones. Low-fat dairy products are high in calcium, and many are fortified with vitamin D and help strengthen bones. Fatty fish such as salmon, mackerel, tuna, and sardines are high in vitamin D. Canned sardines and salmon (with bones) are high in calcium.

"Calcium and Vitamin D: What You Need to Know." National Osteoporosis Foundation. 2020.