Hearts by the numbers

What’s in a blood pressure number?

As I paged through the Parade magazine that arrived with my newspaper this past weekend, my attention was grabbed by Dr. Oz’s health column on page 7, specifically this statement about heart health:

Blood pressure is the largest driver of heart disease; ideally it should be 115/70.

I confess to doing a bit of a doubletake. 115 over 70? What happened to the standard yardstick of 120/80?

It’s not an idle question. High blood pressure is one of the most common cardiovascular conditions, so where the threshold is set is a matter of importance to millions of Americans.

As it turns out, the answer isn’t all that straightforward. Once upon a time, optimal blood pressure was determined by adding your age to a baseline of 100 – a method that wasn’t particularly evidence-based or useful. As researchers tracked large populations to see how they fared over the course of many years, a consensus emerged: People were less likely to have a stroke or heart attack if their blood pressure was maintained at 140/90 or  lower.

This became the goal to which patients and their doctors aspired. But with more research came more nuances. In 2003 the National Institutes of Health identified a new, and lower, “normal”: 120/80. The guidelines also created a category known as prehypertension, defined as systolic readings of 120 to 139 and diastolic readings of 80 to 89, a range previously considered “high normal” but now thought to elevate the risk of heart disease

As a result, 120/80 or lower became the gold standard for successfully managing high blood pressure.

(For an easy-to-read breakdown of the stages of hypertension, check out this chart from the American Heart Association, or this one from the Mayo Clinic.)

So where does 115/70 fit in? Has the threshold for risk been ratcheted down even further, and are we headed for trouble if we don’t achieve these numbers?

Maybe not. Nowhere does this appear to be a new official guideline – not by the American Heart Association, the American Society of Hypertension, the Heart, Lung and Blood Institute, nor the U.S. Preventive Services Task Force, which evaluates the scientific evidence and makes recommendations for clinical practice in everything from pain management for arthritis to the best use of antidepressants.

In fact, there appears to be no such thing as an “ideal” blood pressure value, although there’s certainly a range that’s considered optimal; 120/80 obviously is better for overall health than, say, 160/100. I had to do some online digging but finally came up with the apparent basis for the numbers cited by Dr. Oz: 115/70 appears to be the cut-off point at which researchers have seen no evidence of increased risk for cardiovascular disease.

Is this a number we all should strive for, then? Well, I don’t know. Most American adults – especially those middle-aged and older – are unlikely to achieve that target without serious lifestyle changes, prescription medications or both. What’s more, a too-aggressive approach to lowering blood pressure comes with risks of its own, such as increased likelihood of dizziness and falls, not to mention the increased costs of all those drugs.

To complicate the picture further, evidence has emerged that suggests even prehypertension doesn’t necessarily raise the risk of dying from a stroke or heart attack. A study published last year in the Journal of General Internal Medicine analyzed data from the National Health and Nutrition Examination Survey and concluded that people with prehypertension were no more likely to die prematurely of heart disease than those whose blood pressure was categorized as “normal.” What seemed to matter were the individual systolic and diastolic numbers and the person’s age. Systolic readings consistently over 140 were associated with higher risk among people 50 and older, whereas it was the diastolic number that was more predictive among those younger than 50.

This particular study looked only at mortality and did not attempt to quantify the risk of non-fatal heart attacks and strokes among people with elevated blood pressure. Meanwhile, the state of knowledge is continuing to evolve. The last time the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure revised its guidelines was back in 2003; an update is in the works and scheduled to be released this year, possibly refining our understanding of the picture even further.

It would probably be safe to say that there’s more to blood pressure management than achieving a simple, standard set of numbers. While Dr. Oz’s benchmark of 115/70 might not have been wrong, technically speaking, it’s not the whole story. We’d do well to ask ourselves what these numbers really mean and whether there’s all that much to be gained before adopting this as a new goal.