Q. How do doctors interpret a bone mineral density (BMD) report?

A. DXA (dual energy x-ray absorptiometry) measures bone mass at two sites - the lumbar or lower spine and the hip. The vertebrae or bones of the spine all have numbers. The test looks at the bones L1 to L4. DXA looks at several areas of the hip, most notably the femoral neck.

To diagnose osteoporosis, doctors compare the bone mass with two different standards. The first comparison is with young adults of the same sex. This provides a measure of peak bone mass called the T-score. The second comparison is to age, weight, sex and race-matched controls. This is known as the Z- score.

For a given BMD, the T-score is the number of standard deviations below the mean of young adult controls. (A standard deviation is a consistent unit of measure above or below a zero point that is considered normal). The Z-score gives the SD below the mean of age-matched controls.

A committee of the World Health Organization has defined osteoporosis in adults based on BMD:

• Normal bone density is present when the T-score is greater than or equal to -1.0
• Osteopenia, or mild bone loss, is present when the T-score at either the hip or spine is less than -1.0 but greater than -2.5
• Osteoporosis is defined as a T-score below -2.5
• Severe osteoporosis is said to be present when an individual has sustained a fragility fracture.

Q. What is the relationship between bone mass and fracture risk?

A. There is a direct relationship between bone mass and fragility fractures. For each SD decline in BMD, there is about a two-fold increase in the risk of fracture. For example, with a T-score of -1.0, the fracture risk doubles, while at a T-score of -3.0, the fracture risk increases to 8 times that of a young adult.

Although people sometimes compare measuring bone density to assess osteoporosis risk with measuring cholesterol to assess cardiovascular risk, the relationship between bone mass and osteoporosis is actually more direct.

Q. Can calcium and exercise prevent/treat postmenopausal osteoporosis?

A. Lifetime management to maintain bone should include:

• avoiding lifestyle risk factors (no smoking, low intake of alcohol and caffeine)
• daily calcium rich foods and vitamin D to enhance calcium absorption
• improvement in walking and with balance
• daily weight bearing exercise

Through diet and supplements, postmenopausal women require 1,200 mg to 1,500 mg of elemental calcium and 400 to 800 international units of vitamin D daily. The typical North American diet contains 200 mg to 300 mg of elemental calcium (one glass of milk has 300 mg).

Daily calcium is important to prevent bone loss associated with the decrease in estrogen in postmenopausal women but it is not enough on its own. High calcium intake may decrease the rate of bone loss in the elderly, however, it has not been shown to prevent age or menopause-related bone loss on a regular basis.

Several studies show that weight-bearing exercise has a positive effect on bone density, making bones stronger and less fragile. Exercise has also been shown to improve the effect of other therapies (for example, combined with drug treatment).

Increased exercise is also important for:

• easy body movement
• increase in muscle strength
• improvement in walking and with balance
• stronger muscles which lead to a decreased risk of falling

Q. How can I prevent fractures?

A. Fractures are a potential major consequence of osteoporosis. The risk increases with age and decreasing bone mineral density. The best way to avoid a fracture is to avoid falling (to prevent hip and wrist fractures) and to maintain good back care/posture (to minimize risk of spine fractures). Use these links for practical tips on fall prevention and on modifying your daily activities to protect your back.

Some medical conditions and medications and medical conditions can interfere with strength, co-ordination, posture and balance. These factors increase the risk of falling and fracturing your hip. The potential risk of these issues can be addressed with your health care provider. A visual impairment can also increase the risk of falls and fractures.

For older people, fall prevention strategies are an important part of the treatment plan. The best way to develop these strategies is to have an occupational therapy assessment for your home or workplace. A physiotherapist can help by explaining how to exercise for strength, balance and flexibility.