Some nights the newscasts make it seem unsafe to eat, breathe, exercise or sit still. Yet even as the number of hazards in our daily lives seems to be multiplying, reports of treatment breakthroughs and advances in scientific understanding abound. It may be tempting to discount the warnings when danger seems all around us, yet should we also discount the good news? The answer in many cases is "yes" to both.
In fact, some of the dramatic risks and breakthroughs you may hear about are not so impressive when you consider three common pitfalls in how medical news is reported and interpreted:
- An association between a possible risk factor and a disease is often mistakenly assumed to mean that the risk factor causes the disease.
- Relative risk (that is, your risk in relationship to the risk of others) is reported without mention of absolute risk.
- Preliminary research is assumed to be the last word.
The Difference Between Association and Cause
Take a June 2001 study that found an increased risk of breast cancer among women older than 65 with high bone density. If you read only the headline or briefly glanced at the article, it might appear that high bone density causes breast cancer. Yet high bone density generally has been viewed as a good thing because it helps to avoid the complications of osteoporosis, a disorder of low bone density in which hip, wrist and spine fractures may occur. Does this mean a woman should strive for high bone density, which may put her at risk of breast cancer, or should she accept low density and osteoporosis?
A more complete reading of the story sorts this out. "Bone density … is not a cause of breast cancer, but it is an indirect measure of levels of hormone, such as testosterone and estrogen, that have been linked both to bone density and to breast cancer." The real news of this report is that higher bone density is associated with an increased risk of breast cancer (and may help predict its development), not that higher bone density will cause breast cancer.
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Relative Vs. Absolute Risk
Consider the near panic over phenylpropanolamine (PPA) in the fall of 2000. Many news outlets reported a dramatic increase in the risk of stroke among patients taking this medication, which is an ingredient in appetite suppressants and many over-the-counter cold remedies. According to a study summarized on the news, a woman taking PPA for a cold tripled her risk of stroke; the risk was even higher if she took PPA in the form of an appetite suppressant.
Although that sounds bad, realize that this is a relative risk — one risk (that of women taking PPA) compared with another (that of women not taking PPA). The absolute risk of developing a stroke while taking PPA is estimated at 1 or 2 in 1 million. Although PPA appears to increase the risk of stroke, the chances of PPA causing serious harm when taken for cold symptoms are quite small. (As a result of these concerns, and the fact that effective cold remedies without PPA are available, the U.S. Food and Drug Administration recommended a voluntary recall of products containing PPA.)
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Preliminary Research and Cautious Optimism
Most medical advances are realized gradually. Well before a definitive study can demonstrate safety and effectiveness in people, studies in animals and small trials in humans are required. These small, preliminary studies are critical because many drugs or treatments do not deliver on their early promises. For this reason, many reports of breakthroughs that are based on small, preliminary studies do not deserve the publicity and excitement they generate. Although cautious optimism may be entirely appropriate, it is not always easy to see past the pronouncements of "cures" and "major findings."
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The Bottom Line
At its best, medical news keeps us updated on the latest advances in maintaining health and fighting disease. But sometimes it generates or perpetuates medical myths by overestimating the importance of research findings. You can be better informed by remembering the difference between an association and a cause, by looking for absolute (not just relative) risk in the story, and by recognizing that there is a good reason many medical reports sign off with a familiar phrase: "More study is needed."
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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.