There’s a study out this week that’s gotten major headlines: Therapy with a statin may lower cardiovascular disease risk by about 50%, even in those with normal cholesterol. Sounds great, right? Not so fast. This may indeed be good news, but it’s much more complicated than the headlines suggest.
First of all, let’s talk for a minute about what a 50% decrease in risk means. Let’s say, for instance, that you had a crystal ball and knew that you had a 1 in 4 (25%) chance of having a heart attack in the next 10 years. (There are ways to guess at this risk for any given person, using their age, gender, blood pressure, cholesterol, and smoking history.) If a magic pill could cut your risk by 50%, you’d only have a 1 in 8 (12.5%) chance of having that heart attack.
Put another way, if I gave 100 people with a 1 in 4 chance of a heart attack that magic pill, I’d avoid about 12 heart attacks. Not too bad.
But what if you didn’t start with a 1 in 4 chance, but a 1 in 20 chance (5%) of having that heart attack? I might still have a magic pill to cut your risk in half. But now, we’re talking about decreasing the risk from 1 in 20 to 1 in 40 (2.5%). Now if I gave 100 people like you the magic pill, I’d only be preventing 2 or 3 heart attacks. And the other 98 people might not get any benefit.
In the study, the authors calculated that, given the statistics involved, doctors would need to treat about 25 patients for four years to prevent a cardiovascular event or death. That one person who benefits might certainly think it worthwhile—but that’s a lot of medication and a lot of health-care costs. And the 24 people who didn’t see a benefit would have been on a drug that can have side effects for a long period of time. It’s not an easy recommendation to put into practice without more thought.
So every time you hear about a 20% or 30% or 50% decrease in risk based on a given treatment, consider whether the condition being treated is really one that you or your family member is at high risk of having happen. This information is rarely given in the media coverage of new therapies, but it’s a critical piece of data you need before making your own medical decisions.
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