On Science: Losing bone: Osteoporosis
This article first appeared in the St. Louis Beacon, May 6, 2009 - My wife and I invited friends over to watch the Kentucky Derby last weekend. We try to do this every year, as we love the semi-ridiculous over-the-top feel of Derby Day. Not so much fun last year, when one of the horses fell at race's end with fractured ankles. It got me thinking about bone fractures.
I am no race horse, don't stress my ankles and don't expect to have to be put down anytime soon, but I do walk, run, jump, swim (rarely) and even squirm through the mud on occasion. How are MY bones doing?
The bones that make up my and your skeleton are not lifeless, like the scaffolding of a building, but rather living tissue that continues to grow and change throughout our lives. Just because we reach our full height does not mean that our bones stop growing. They stop elongating, but that is merely one aspect of bone growth. Every day of your life, your bones are adding new tissue and breaking down old tissue, reshaping your skeleton to meet the needs of your body.
If you break a bone, your body heals the fracture by adding new bone tissue at the site of the break. However, when the process of forming new bone is impaired, the bone becomes weak and unable to heal itself. A striking example of the impact of this failure of bone healing is exhibited by the little old lady that you might see walking down the street with a hunched back. The bump on her back is caused by an imbalance in bone metabolism, rather than poor posture.
As a person ages, the backbone and other bones tend to lose bone mass much faster than new bone mass is produced. Excessive bone loss is a condition called osteoporosis.
A section of normal bone is shown in the top photo. A section of bone from a patient with osteoporosis is shown in the bottom photo. You can see how much less bone tissue is present in the osteoporosis bone.
Unfortunately for the person suffering from osteoporosis, even everyday activities such as bending or lifting can result in a broken bone. The little old lady with the humped back has already experienced multiple bone fractures in her spine.
Although we often refer to it as the "backbone," the spine is not one bone but rather a column of many smaller bones stacked one on top of the other, like building blocks. The spine holds the upper body erect and in a person with osteoporosis, just the stress of the body's weight on the weakened bones cause small fractures up and down the spine.
Multiple spine fractures can result in a curvature of the back and a stooped posture.
A loss of height of an inch or more is often an early sign of osteoporosis.
How does a person know if they have osteoporosis? Unfortunately, a fractured bone is usually the primary warning sign of osteoporosis.
There are diagnostic tests that can check a person's bone density, but they often aren't done unless a person experiences a fracture. A bone density test should be performed when a person over 45 breaks a bone or in a person less than 45 who has had several fractures. The test used to diagnose osteoporosis, a bone density test measures the density, or mass, of the bones. The hips, spine and wrists are often used for evaluation because these are the bones most commonly broken due to osteoporosis.
A bone density test called DXA, for dual X-ray absorptiometry, is considered the gold standard test for diagnosing osteoporosis and monitoring bone loss over time. The test is a noninvasive low-dose X-ray. Actually, two X-rays of different energy levels (or wavelengths) are used to differentiate between bone and soft tissue. This provides a very accurate measurement of bone density.
The bone density of the patient is compared to that of a healthy 30 year old, which is when bone density is highest in both male and females, and a number known as a T-score is assigned. A T-score of one or above is normal. A negative T-score indicates that some bone loss has occurred. A number between -2.5 and -1 suggests an increased risk of fractures with a 10 percent-30 percent loss in bone density, while a value below -2.5 indicates osteoporosis.
Osteoporosis is often called a "silent disease" because symptoms usually aren't apparent until a fracture occurs. However, one out of every two women over 50 years of age experiences clinical bone loss to some degree. The incidence of osteoporosis is considerably less in men, with about one out of every four men experiencing bone loss.
More than 10 milion people in the United States have osteoporosis with twice that many at risk. Osteoporosis causes about 1.5 million fractures a year in men and women, with spine and hip fractures making up the majority of these.
Of the 10 million Americans affected by osteoporosis, more than 80 percent are older women. Osteoporosis is most prevalent in postmenopausal women over the age of 50.
The process of building up bone and breaking it down is controlled by various hormones in the body, chemical signals released into the bloodstream that control body functions. As a woman's body experiences changes in various hormone levels after menopause, some body functions, including the cyclic building up and breaking down of bone tissue, are altered. Other factors also contribute to osteoporosis including family history, inadequate sources of calcium and vitamin D in the diet, smoking, ethnicity (caucasian and asian women have a higher risk) and lack of exercise.
Is osteoporosis unavoidable? Not at all. Doctors are learning more and more about osteoporosis and how to treat it, and importantly, how to prevent it. Although it is a disease found most frequently in the elderly, it can be prevented by actions taken when a person is younger. Actions taken in your 20s can reduce the chance of your developing osteoporosis much later in life.
How can you avoid osteoporosis later in life? The "sculpting" of bone occurs throughout your lifetime, but it is in your childhood and teenage years when new bone is added at a faster rate than it is lost by the breakdown of bone tissue. This net addition of bone tissue continues until a person reaches about 30 years of age, when the balance begins to tip toward the direction of bone loss. Osteoporosis develops when the rate of bone loss exceeds the replacement of bone to the point the bone becomes weak and brittle.
Bone forms when calcium phosphate hardens around collagen fibers and so an adequate supply of calcium is important to healthy bone development. Because of this, it is important that children and teenagers have enough calcium in their diets to fulfill the needs of developing bone, as well as other body activities that require calcium.
Therefore, the best way to avoid osteoporosis in your elder years is to get ample amounts of calcium before you're 30. Building up strong, healthy, dense bones before 30 means that you have a larger pool of calcium in your bones to offset bone loss in your older years.
As people age, their bodies are less efficient at absorbing calcium and so people over 50 actually need to increase their calcium intake to 1,200 mg per day. Foods high in calcium include low-fat dairy product, dark green leafy vegetables, orange juice. Many people take calcium supplements to ensure that they get enough calcium.
Physical activity is also key to preventing osteoporosis, but it is important that the activity involves weight-bearing exercise such as walking or jogging. New bone tissue is added to areas of the bone that are stressed to make those areas stronger. Weight-bearing exercises, both in young and old, help to strengthen areas of the bone that might be most susceptible to fractures.
So watching the Derby, and thinking of bone fractures, was sort of a sad experience. Running all this over in my mind, the best treatment for osteoporosis is to avoid getting it by building up your bones when you're young. Unfortunately, I haven't been there in a while. My three daughters are going to get a lecture when they come home from college next month, though.
George B. Johnson's "On Science" column looks at scientific issues and explains them in an accessible manner.
Johnson, Ph.D., professor emeritus of Biology at Washington University, has taught biology and genetics to undergraduates for more than 30 years. Also professor of genetics at Washington University’s School of Medicine, Johnson is a student of population genetics and evolution, renowned for his pioneering studies of genetic variability. He has authored more than 50 scientific publications and seven texts.
As the founding director of The Living World, the education center at the St Louis Zoo, from 1987 to 1990, he was responsible for developing innovative high-tech exhibits and new educational programs.
Copyright George Johnson