Osteoporosis

Alexandra M. Burgar, M.D.

Definition

Osteoporosis is Greek for “porous bone,” and a disease characterizedby low bone mass and structural deterioration of bone tissue leading tobone fragility and increased susceptibility to fractures. Thesefractures occur most commonly in the spine, hip and wrist, but canoccur in any bone.

Osteoporosis has been called “a pediatric disease with geriatricconsequences,” because the bone mass attained in childhood andadolescence is an important determinant of lifelong skeletal health.The health habits your kids are forming now, can make, or literallybreak, their bones as they age.

Fast Facts

• Called the “silent” disease — bone loss can occur without symptoms
• 80% of patients affected by osteoporosis are female
• 1 in 2 females and 1 in 4 males over age 50 will have an osteoporosis
• related fracture in their lifetime
• Responsible for greater than 1.5 million fractures annually
• A woman with a hip fracture is 4 times at risk to develop a second fracture
• Women can lose up to 20% of their bone mass within 5-7 years following menopause
• An average of 24% of hip fracture patients over 50 die within one year of their fracture

What is Bone?

In order to understand osteoporosis, it is important to learn aboutbone. Made mostly of collagen, bone is a living, growing tissue.Collagen is a protein that provides a soft framework. Calcium phosphateis a mineral that adds strength and hardens the framework. Thiscombination of collagen and calcium makes bone strong enough towithstand stress. More than 99 percent of the body’s calcium iscontained in the bones and teeth. The remaining 1 percent is found inthe blood.

There are two types of bone found in the body – cortical andtrabecular. Cortical bone is dense and compact. It forms the outerlayer of the bone. Trabecular bone makes up the inner layer of the boneand has a spongy, honeycomb-like structure.

Bone continually undergoes a two-part process called remodeling, orbone turnover. It involves two distinct stages: bone resorption(breakdown) and bone formation. Calcium is stored in bone. When it isneeded in the body, bone resorption increases. Bone cells calledosteoclasts attach to the bone surface and break it down, leavingcavities in the bone and releasing calcium. In bone formation,bone-forming cells called osteoblasts move in and release collagen andother proteins into these cavities and stimulate bone mineralization.The osteoblasts then join with calcium and other substances to form newbone material (matrix) to replace what was lost. Some of theseosteoblasts which remain part of the matrix are called osteocytes.Osteoclast and osteoblast function is regulated by several hormonesincluding calcitonin, parathyroid hormone, vitamin D, estrogen (inwomen) and testosterone (in men), among others.

Thinkof bone as a bank account where you “deposit” and “withdraw” bonetissue. During childhood and the teenage years, new bone is added tothe skeleton faster than old bone is removed. As a result, bones becomelarger, heavier, and denser. For most people, bone formation continuesat a faster pace than removal until bone mass peaks during the thirddecade of life.

In order to be able to make “deposits” of bone tissue and reach thegreatest possible peak bone mass, you need to get enough calcium,vitamin D, and exercise – important factors in building bone.

After age 30, bone “withdrawals” can begin to exceed “deposits.” Formany people, this bone loss can be prevented by continuing to getcalcium, vitamin D, and exercise and by avoiding tobacco and excessivealcohol use. Your body continually removes and replaces calcium fromthe bone. If more calcium is removed than replaced, the bone becomesweaker and has a greater chance of breaking. Osteoporosis develops wheneither bone removal occurs too quickly or replacement occurs too slowlyor both. You are more likely to develop osteoporosis if you did notreach your maximum peak bone mass during your bone building years.

Factors Affecting Peak Bone Mass

Peak bone mass is influenced by a variety of factors: some that youcan’t change, like gender and race, and some that you can, likenutrition and physical activity.

Gender: Bone mass or density is generally higher in men thanin women. Before puberty, boys and girls develop bone mass at similarrates. After puberty, however, boys tend to acquire greater bone massthan girls.

Race: For reasons still not well understood, African-American girlstend to achieve higher peak bone mass than Caucasian girls, andAfrican-American women are at lower risk for osteoporosis later inlife. More research is needed to understand the differences in bonedensity between the various racial and ethnic groups. However, becauseall women, regardless of race, are at significant risk forosteoporosis, girls of all races need to build as much bone as possibleto protect themselves against this disease.

Hormonal factors: Sex hormones, including estrogen and testosterone,are essential for the development of bone mass. Girls who start tomenstruate at an early age typically have greater bone density. Thosewho frequently miss their menstrual periods sometimes have lower bonedensity.

Nutritional status: Calcium is an essential nutrient for bonehealth. In fact, calcium deficiencies in young people can account for a5 to10 percent lower peak bone mass and may increase the risk for bonefracture in later life. A well-balanced diet including adequate amountsof vitamins and minerals such as magnesium, zinc, and vitamin D is alsoimportant for bone health.

Physical activity: Important for building healthy bones, physicalactivity provides benefits that are most pronounced in the areas of theskeleton that bear the most weight. These areas include the hips duringwalking and running and the arms during gymnastics and weight lifting.

DETECTION

Special tests to assess osteoporosis are called Bone Mineral Densitytests. BMD tests measure bone density, or amount of calcium buildup atvarious sites. These tests can detect osteoporosis, predict chances offracture in the future, and determine the rate of bone loss withrepeated tests every 2 years.

The National Osteoporosis Foundation recommends BMD tests in thefollowing: all female patients over 65, younger, post-menopausal womenwith greater than one risk factor for osteoporosis, and post-menopausalwomen who present with a fracture to confirm the diagnosis anddetermine bone density.

Bone Mineral Density testing ispainless, noninvasive and safe. Bone mineral testing when completed iscompared to 2 standards. The first standard is age matched (Z score) —it compares the patient’s bone density to the expected density ofsomeone of the same age, sex and size. The second standard is the youngnormal (T score) — it compares the patient’s bone density to theoptimal peak density of a healthy young adult of the same sex.

TREATMENTS

Medication

Although there is no cure for osteoporosis, medications may be usedto prevent and or treat osteoporosis. These medications includeBisphosphonates, Estrogen/Hormone Therapy, and Selective EstrogenReceptor Modulators (SERMs).

Bisphosphonates affect the bone remodeling cycle and are classifiedas anti-resorptive medications. Anti-resorptive medications slow orstop the bone-resorbing portion of the bone remodeling cycle. They donot slow the boneformation portion of the cycle. As such — the new boneformation builds faster than the resorption, therefore the bone densitymay increase over time.

Estrogen or Hormone therapy has been shown to reduce bone loss andincrease the bone density in both the spine and the hip. Due to theincreased risk of developing other cancers with continued estrogen use,Healthcare providers prescribe the hormone progestin with estrogen tominimize this risk.

Selective Estrogen Receptor Modulators (SERMs) have been developedto provide the beneficial effects of estrogens without the potentialdisadvantages and side effects.

Nutrition

Calcium is essential for many of the body’s functions. Calcium is a mineral found in many foods. Adequate calcium intake is important because the human body cannot produce calcium. When reaching full skeletal growth, adequate calcium intake is important because the body loses calcium every day through the skin, nails, hair and sweat. Lost calcium is replaced daily from the diet. Without adequate intake through the diet, the body tries to replenish it by absorbing it through the bone. With increased amounts of calcium loss, the bone becomes weaker and more susceptible to fractures.

Vitamin D helps the body absorb calcium. It allows the body to absorb calcium into the bloodstream. The active or body tolerant form of vitamin D is activated by skin exposure to sunlight. 10-15 minutes a day of sunlight exposure to the hands and face will allow the vitamin D to become active and allow the body to absorb calcium. The recommendation for Vitamin D intake is 200-600 IU a day.

Prevention

Childhood Bone Development

Experts believe calcium should come from food sources whenever possible. However, if you think your children are not getting adequate calcium from their diet, you may want to consider a calcium supplement. For optimal absorption, no more than 500 mg of calcium should be taken at one time. Muscles get stronger when we use them. The same idea applies to bones: the more work they do, the stronger they get. Any kind of physical exercise is great for your kids, but the best ones for their bones are weightbearing activities like walking, running, hiking, dancing, tennis, basketball, gymnastics, and soccer. (Children who tend to play outside will also have higher vitamin D levels.) Swimming and bicycling promote your kids’ general health, but are not weight-bearing exercises and will not help build bone density. Organized sports can be fun and build confidence, but they are not the only way to build healthy bones.

Osteoporosis is rare among children and adolescents. When it occurs, it is usually caused by an underlying medical disorder or by medications used to treat such disorders. If you are concerned about your child’s frequent fractures, talk to their doctor for more information.

Beyond Childhood

By age 20 the average female has acquired 98% of her skeletal mass. Therefore building strong bones during childhood and adolescence is the best defense.

To optimize bone health — the following guidelines should be considered:

• Balanced diet rich in calcium and vitamin D
• Weight-bearing and resistive training exercises
• Healthy lifestyle — no smoking or excessive alcohol intake
• Talking to your health care professional about bone health
• Bone mineral density tests and medication when appropriate

Risk Factors

Factors which increase the likelihood of developing osteoporosis may include:

• history of fracture after age 50
• current low bone mass
• female
• low body weight (less than 85% ideal body weight or less than 120 pounds)
• thin, or small frame
• advanced age
• family history
• estrogen deficiency
• anorexia nervosa
• inadequate calcium intake
• vitamin D deficiency
• use of certain medications (corticosteroids, chemotherapy, anticonvulsants)
• decreased testosterone (men)
• inactivity
• smoking
• excess alcohol

World Health Organization Definitions of Osteoporosis Based on Bone Density Levels (T score)

• Normal Bone density is within 1 SD (-1 or +1) of the young adult mean
• Low Bone Mass – Bone density is between 1 to 2.5 SD below the young adult mean
• Osteoporosis – Bone density is greater than 2.5 SD below the young adult mean
• Severe/Established Osteoporosis – Bone density is greater than 2.5 SD below the young adult mean and a history of one or more osteoporotic fractures

Recommended Calcium Intakes*

Age Amount of calcium

Infants

• Birth – 6 months 210 mg
• 6 months – 1 year 270 mg

Children/Young Adults

• 1– 3 years 500 mg
• 4 – 8 years 800 mg
• 9 – 18 years 1,300 mg

Adult Women and Men

• 19 – 50 years 1,000 mg
• 50+ 1,200 mg

Pregnant or Lactating Women

• 18 years or younger 1,300 mg
• 19 – 50 years 1,000 mg

* Source: National Academy of Sciences, 1997.

Sources

• National Institute of Arthritis and Musculoskeletal and Skin Diseases
• National Osteoporosis Foundation
• National Institute of Health
• National Academy of Sciences Institute of Medicine
• American Academy of Orthopedic Surgeons