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 During childhood and adolescence, much more bone is deposited than withdrawn, so the skeleton grows in both size and density.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

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

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

Estrogen
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
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.

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