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Osteoporosis is a condition marked by reduced bone strength, which can lead to an increased risk of fractured, or broken, bones. The strength of a person’s bones is affected by their bone mass (amount of bone) and bone quality. Osteoporosis is the major underlying cause of fractures in postmenopausal and older women. Fractures occur most often in bones of the hip, spine and wrist, but any bone can be affected. Some fractures can be permanently disabling, especially when they occur in the hip.

Osteoporosis usually progresses without symptoms until a fracture occurs. In some cases, bones affected by osteoporosis can become so fragile that fractures occur spontaneously or as the result of minor bumps, falls, or normal stresses and strains such as bending, lifting or even coughing.

Many people think that osteoporosis is a natural and unavoidable part of aging; however, medical experts now believe that osteoporosis is largely preventable. People who already have osteoporosis can take steps to prevent or slow the progression of the disease, and reduce their risk of fractures. Although osteoporosis was once viewed primarily as a disease of old age, it is now recognized as a disease that can stem from less-than-optimal bone growth during childhood and adolescence, as well as from bone loss later in life.

Bone remodelling

Bones are living, growing tissue. During our lifetime, bone is constantly being renewed. The old bone is removed and the new bone is laid down. This process is called bone remodelling. We are so efficient at remodelling that we are able to replace our entire skeleton every 10 years!

Remodelling has two purposes. First, by remodelling, the bone is able to repair microfractures – tiny microscopic cracks that occur in the bone with daily activity. This repairing of microfractures helps to prevent osteoporosis fractures. Second, remodelling allows the bone to serve as a source of minerals important to the function of many organ systems.

There are two procesesses involved in remodelling:

  1. Resorption
    Cells called osteoclasts dissolve some tissue on the bone's surface, creating a small cavity. This process usually takes place over a few days.
  2. Formation
    Cells called osteoblasts fill the cavities with a soft protein containing collagen. This hardens when minerals, especially calcium, are deposited on it. Although many systems in our body need calcium to function properly, most of the calcium is in our bones and teeth. Bone formation occurs over the course of several months.

Typically bone formation and bone resorption occur at equal rates so that the quantity and quality of bone are maintained. When the rate of resorption exceeds the rate of formation, which occurs as we age and with estrogen deficiency, the quantity and quality of bone decrease.

Below is an image of normal bone (on the left), where bone formation and bone resporption are equal; and an image (on the right) of porous bone, where resorption exceeds formation, such as we see in people who have osteoporosis.

 Normal Bone  Porous Bone
Normal bone Porous bone

What helps bones to grow?
Hormones (estrogen in women, testosterone in men), an adequate intake of calcium and vitamin D, and weight-bearing exercise are all important to enhance the formation of bone. If the bone removed by resorption is completely replaced, then the amount of bone does not change, and bones stay strong.

What Causes Osteoporosis?

Osteoporosis is characterized by an imbalance in the bone remodelling cycle: too much bone resorption, not enough bone formation, or a combination of excess resorption and decreased formation. The imbalance in remodelling leads to a decrease in the amount and quality of bone, which increases a person’s risk of fractures.

Osteoporosis and Bone Mass
One way to think of bone is as a bank account, where you make "deposits" and "withdrawals" of bone tissue. During childhood and adolescence, much more bone is deposited than withdrawn, so the skeleton grows in both size and density. Up to 90 percent of peak bone mass is acquired by age 18 in girls and age 20 in boys, which makes youth the best time to "invest" in your bone health.

The amount of bone tissue in the skeleton, known as bone mass, can keep growing until around age 30. At that point, bones have reached their maximum strength and density, known as peak bone mass. In women, there tends to be minimal change in total bone mass between age 30 and menopause. But in the first few years after menopause, most women experience rapid bone loss – a "withdrawal" from the bone bank account – which then slows but continues throughout the postmenopausal years. This loss of bone mass can lead to osteoporosis.

Given that a high peak bone density reduces the risk of osteoporosis later in life, it makes sense to pay attention to those factors that optimize our peak bone mass, such as getting enough calcium and vitamin D, doing weight-bearing exercises and avoiding smoking.

Risk factors

Fractures from osteoporosis are about twice as common in women as they are in men.

As a person ages, the quantity and quality of bone decreases. This increases a person’s risk of osteoporosis.

Estrogen plays a critical role in building and maintaining bone. Decreased estrogen, due to natural menopause, surgical removal of the ovaries, or chemotherapy or radiation treatments for cancer, can lead to bone loss and eventually osteoporosis. After menopause, bone loss occurs as the amount of estrogen produced by a woman’s ovaries drops dramatically. Bone loss is most rapid in the first few years after menopause but continues into the postmenopausal years.

The levels of sex hormones in men also decline after middle age, but the decline is more gradual. This decline probably also contributes to bone loss in men after around age 50.

Family history
Osteoporosis tends to run in families. Having a parent, brother or sister who has osteoporosis puts a person at greater risk.

Smoking may decrease a person’s peak bone mass. 

Certain conditions and medications
A wide range of diseases, conditions, medications and medical treatments can cause bone loss, which can result in osteoporosis. This is called secondary osteoporosis.

Causes of secondary osteoporosis include:

  • diseases that affect the endocrine system, such as hyperparathyroidism or hyperthyroidism
  • diseases of the gastrointestinal (digestive) tract, such as Crohn’s and celiac disease (which are associated with poor gut absorption of calcium and vitamin D)
  • smoking
  • chronic alcoholism
  • liver disease
  • premature menopause
  • eating disorders (which cause estrogen levels to drop)
  • a vitamin D deficiency
  • time spent in bed because of illness (which causes us to do less weight-bearing activity)
  • poor nutrition

Medications that can cause osteoporosis include:

  • phenytoin (such as Dilantin, used to treat epilepsy)
  • corticosteroids (such as prednisone and inhaled steroids for asthma)
  • blood-thinning drugs (such as heparin and cyclosporin)
  • some antacids used for heartburn (such as Nexium, Prevacid, Prilosec)
  • diuretics
  • chemotherapy drugs or aromatase inhibitors (used to treat breast cancer)

If you have an illness that needs medication, ask your doctor or pharmacist if either the disease or medication has any effect on your bone mass. Sometimes taking the lowest dose possible to treat a condition can lessen its effect on your bones.

Fractures from osteoporosis

Most osteoporosis-related fractures occur in the hip, spine or wrist.

Hip fractures|
An osteoporosis-related fracture of the hip is usually a break in the area of the bone called the femoral neck. While most fractures result from a fall, they can also occur spontaneously if the osteoporosis is advanced. In 1988, Canadians had approximately 15,000 hip fractures, 70 per cent of which can be attributed to osteoporosis. By 1993, the total number of hip fractures had increased to 25,000. By 2005, there were 28,200 hip fractures. Because the Canadian population is aging, it is estimated that the number of hip fractures will continue to increase significantly.

Twelve to 20 per cent of people who suffer a hip fracture die of related complications. Two-thirds (68 per cent) of hip fracture patients who survive for one year still cannot walk without assistance. That is about twice the number that needed help walking before the hip fracture. An even greater concern is the number of patients who are in wheelchairs or are still bedridden one year after the fracture. This number increases from 6 per cent before the hip fracture to 23 per cent in one-year survivors.

Changes in the shape of the skeletonSpinal fractures
Osteoporosis-related fractures in the spine can occur spontaneously or as a result of a minor trauma, such as coughing, hugging or lifting. Repeated fractures can cause:

  • acute and chronic back pain
  • kyphosis (also known as dowagers hump – the curving forward of the upper spine)

These changes in the shape of the skeleton can be accompanied by:

  • a significant loss of height
  • gastrointestinal or digestive problems
  • respiratory or breathing problems, because of the ribcage pushing on the pelvis

Wrist fractures
Osteoporosis-related fractures of the wrist are usually the result of a fall on the outstretched hand. Wrist fractures are painful, and need to stay immobile in a plaster cast for four to six weeks.

If you think you may have broken your wrist, it is important to see a doctor as soon as possible so that the bones will be properly aligned when healing.

Osteoporosis and men

Men gain more bone mass than women during adolescence and adulthood and they lose less bone later in life. This is why women are twice as likely as men to develop osteoporosis.

However, as in women, sex hormones can play a role in male bone loss. Hypogonadism and the gradual decline of the sex hormone testosterone can cause fragile bones in men. While menopausal women lose bone due to increased bone resorption, men probably lose bone due to decreased bone formation.

Most men who develop osteoporosis earlier in life do so due to secondary causes, such as:

  • excessive alcohol intake
  • tobacco use
  • lack of physical activity
  • low calcium intake
  • reduced strength and activity due to an illness
  • small build or leanness
  • drug therapy, for example, long-term use of corticosteroids, such as prednisone (used to treat rheumatoid arthritis, asthma and Crohn's disease)

Treating male osteoporosis
Treatment for men with osteoporosis can include:

  • weight-bearing exercise
  • fall prevention
  • increased calcium and vitamin D intake
  • medication, such as bisphosphonates
  • hormone therapy using testosterone

More research and education is needed to help us prevent and treat osteoporosis in men.


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Medical description

Bone remodelling

What causes osteoporosis?

Fractures from osteoporosis

Osteoporosis and men

  • A publication of:
  • Women's College Hospital