Some people just can’t catch a break. For years now, physicians have been telling patients that normal blood pressure is anything below 140/90, and if you fell below this number you were A-OK in the blood pressure department. Well, some of these folks probably got a rude surprise if they read about a study published in the New England Journal of Medicine. This study looked at people with “high-normal” blood pressure (systolic BP 130-139, diastolic BP 85-89), people that were previously felt to be out of danger from the perils of hypertension. What the study found was that these folks were actually still two to three times as likely to have heart attacks or strokes than were people with lower normal values.
This is an especially important finding for people with diabetes, because the adverse effects of high blood pressure tend to be magnified in these folks. While it remains to be seen if treating people with “high-normal” blood pressure with drugs or non-pharmacologic means (like with diet or exercise) will help them, I suspect that the answer will be yes when the appropriate studies on large numbers of patients are finally completed.
But that’s not what motivates me to write about this topic. I believe that there’s a hidden truth in studies like the one cited above that will begin to emerge over the next decade or so. I’m talking about the quest for absolute guidelines in medicine, an approach that works because it’s the best we can do, but which I feel is philosophically bankrupt.
Let’s spell out the problem: Doctors want to know if their methods achieve the desired results. If it is common practice to treat high blood pressure only once it tops 140/90, then we need to look at that practice dispassionately and assess if there might be a better way. So, researchers look at large numbers of people and come up with results such as I described above. Out of these results come guidelines with which doctors and patients can make rational choices about therapy. This all makes sense, and there’s no doubt that these guidelines have helped a great many patients and physicians alike.
The problem with this is that absolute guidelines based on studies in whole populations do not take into account the fact that doctors don’t treat populations. They treat individuals. Patients are genetically distinct from one another and surrounded by their own unique environments. We know this in our bones–how often do you hear someone say something like “That guy has smoked like a chimney for thirty years and he’s healthy as a horse, so how come this other person gets lung cancer?” Or, “Bob eats everything he wants to and stays skinny, but Ed watches his diet and still gains weight.” Individuals have very different propensities for disease, even within the same family or community.
This problem affects every medical condition, but the issue is very prominent in diabetes. Some people will get diabetes if they gain just a few extra pounds, while others will avoid the problem even if grossly obese. Similarly, there are studies that show that if your hemoglobin A1c is below 8%, it’s probably acceptable. Other studies show that there is no hemoglobin A1c threshold for diabetic complications, which is why we recommend that control be as tight as tolerable. The truth is that some people will be fine with a hemoglobin A1c of 8%, while others are not as fortunate. We just don’t know which people are which until it’s too late.
And that’s where I think the biggest advances will be made in the upcoming decade or so. We are going to learn which genes predict good and bad outcomes in diabetes, and we are going to be able to tailor our recommendations to individual patients. I believe that we’ll be able to tell someone that a blood pressure of 140/90 is OK for them, while the next patient might need medication even with a pressure of 130/80. In the meantime, absolute guidelines are worth following because they bring at least some evidence to bear on the complex decisions that patients and their doctors must make every day. But the next phase is coming, and I can’t wait.
Vasan R. S., Larson M. G., Leip E. P., Evans J. C., O’Donnell C. J., Kannel W. B., Levy D. Impact of High-Normal Blood Pressure on the Risk of Cardiovascular Disease. New England Journal of Medicine 345:1291-1297, Nov 1, 2001