Since worry can increase your blood pressure, it’s counterproductive to fret about the recent alarming headlines declaring that hypertension now affects half of all Americans, including about 80 percent of those over 65.

The numbers don’t reflect a sudden decline in the public’s health. Instead, health authorities have expanded the definition of hypertension so it now includes some 30 million more people. And yet despite this dramatic shift, surprisingly little has changed in the scientific understanding of hypertension, or in what your doctor is likely to recommend.

The news this month was that the American Heart Association and the American College of Cardiology have just lowered the bar for high systolic blood pressure (which is the top number). It used to be 140, and now it’s 130. While the New York Times announced that now tens of millions of Americans will “need” to lower their blood pressure, the health police are unlikely to arrest you for a reading of 131. A better phrasing might have been that tens of millions more people might benefit from lowering their blood pressure — but many of those people already knew that.

For most people in that newly diagnosed range, which used to be called pre-hypertension, the recommendation is not necessarily to take drugs, but to try lifestyle changes, such as exercising and eating less junk food — the same stuff doctors have been nagging people about for decades. These changes can have positive effects across the board. For some people who already lead a healthy lifestyle, it’s still acceptable for doctors simply to keep an eye on things.

The only substantial change in scientific understanding comes from a 2015 study, said Raymond Townsend, director of the hypertension program at the University of Pennsylvania. Called SPRINT — for Systolic Blood Pressure Intervention Trial — it was actually geared to find the best treatment for people with high blood pressure and other factors that put them at an elevated risk of heart attacks or strokes. These were people who had about a 20 percent chance of dying within the next 10 years.

It was a big trial, including thousands of patients monitored at more than 100 different sites. Some of the participants were treated with drugs aimed at getting their blood pressure below 140. A second group was treated more aggressively, with the goal of getting their readings down to 120. The result was a modest decrease in deaths among those treated more aggressively: For every 200 people given the more aggressive treatment, there was one fewer death.

Here’s how Yale cardiologist Harlan Krumholz interpreted the findings in a New York Times commentary: “If you are age 50 or older, with a top blood pressure number between 130 and 180 (as measured in the study) and are either age 75 or older or have a high risk of stroke or heart or kidney disease, then you have a new option to consider.” That’s not very scary.

That parenthetical point about the way they measured blood pressure in the study matters, say the experts, because blood pressure can swing in and out of the healthy zone over the course of the day and in response to anxiety. SPRINT participants were monitored with multiple readings that were averaged over a period of time. With this more reliable measuring technique, “We’ve found that a lot of people who are thought to be hypertensive are not,” said William White, chief of the division of hypertension and clinical pharmacology at the University of Connecticut School of Medicine.

What does this mean, if anything, for people too healthy to have qualified for SPRINT, but now labeled as hypertensive? “Some of this is really extrapolation,” said White. “We don’t really have any direct evidence that taking someone at 135 and lowering them to 120 will help,” he said. For healthy individuals, that’s “a theoretical construct,” he added.

Though there will be a huge increase in people labeled as having hypertension, he said, the new guidelines don’t necessarily recommend giving those people drugs. Still, he said, earlier guidelines were too lax — defining the healthy range as anything under 150 for people over 60. The higher the blood pressure, the stronger the evidence of danger.

In the best-case scenario, said Penn’s Townsend, the SPRINT findings and new guidelines can be incorporated into an individualized approach. Blood pressure does tend to creep up over time, he said, so people with readings in the 130s or even in the 120s might benefit from exercising or adopting a healthier diet, if they don’t already do those things.

A few more patients might end up taking drugs under the new guidelines, but drug therapy can come with side effects, including harm to the kidneys, dizziness and an increased risk of falls, he said. Prescribing decisions have to weigh individual risks and benefits. He said he hopes doctors won’t be penalized for their patients’ blood-pressure readings under the new guidelines, calling them “no substitute for good clinical judgment.”

In the end, the new guidelines are based on available science, but what the scary stories often leave out is the fact that the science is limited, and there’s a certain amount of extrapolation and educated guessing required. In an interview, Yale’s Krumholz said that doctors should be honest about the uncertainty. The new guidelines shouldn’t be seen as a way of labeling more people with a disease, but as an opportunity for people to work with their doctors to consider different ways to stay healthy over the long run.

Faye Flam, a Bloomberg View columnist, has a degree in geophysics from the California Institute of Technology and has been a Knight-Wallace fellow at the University of Michigan.

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