How bad can a little high blood pressure be? It turns out that it might be worse than we thought.

Fifty years ago, the rule of thumb for a healthy systolic blood pressure (the top number of a blood pressure reading [see “Blood pressure basics”]) was 100 plus your age. Today, a healthy blood pressure is below 120/80. High blood pressure (what doctors call hypertension) is any pressure above 140/90. In the spring of 2003, an expert panel appointed by the National Institutes of Health created a new category—prehypertension. It covers the 25% of Americans in the gray zone between normal blood pressure and hypertension, who have systolic blood pressures between 121 and 139 and/or diastolic pressures between 81 and 89.

Some doctors and pundits scoffed that this new definition was “disease mongering.” A study to be published in the April issue of the journal Neurology indicates that we should take prehypertension seriously.

Blood pressure basics

When the heart contracts, the pressure in the arteries rises—that’s your systolic pressure, usually written as the first number of a blood pressure reading. When the heart relaxes between beats, the pressure falls—that’s your diastolic pressure. The ideal blood pressure is 120/80.

Researchers from Southern Medical University in Guangzhou, China, examined the results of 19 high-quality studies looking at links between prehypertension and stroke. The studies included more than three-quarters of a million people, whose health and wellbeing was followed for 36 years. The researchers broke down the participants into two groups:

Low-range prehypertension: Blood pressure between 120/80 and 129/84

High-range prehypertension: Blood pressure between 130/85 and 139/89

People with high-range prehypertension had a 95% higher stroke risk compared to people with blood pressures less than 120/80. Those in the low-range had a 44% higher stroke risk.

Lifestyle changes lower health risks

The size of the study and the length of the followup make the results believable. They don’t mean that we should elevate prehypertension to a disease. But they do signal that we need to take it seriously.

How seriously? So far, there’s no solid evidence that people with prehypertension benefit from taking medications. Blood pressure drugs lower blood pressure, but they can also cause harmful side effects. In the prehypertension range, benefits and risks seem to cancel each other out.

Instead, lifestyle changes are the way to go for prehypertension. Here are several changes that can lower blood pressure:

If you smoke, quit

Strive to maintain a healthy weight.

Stay physically active as much as you can all day.Get at least 30 minutes of moderate intensity exercise most days of the week.

Make vegetables and fruits half of every meal. Potatoes don’t count as a vegetable.

For the other half, aim for healthy protein and whole grain carbohydrates.

Cut back on the amount of salt and sodium you take in. Much of the salt and sodium we consume comes from packaged foods, so check labels.

Drink water instead of sugary beverages.

If you drink alcohol, keep it moderate. That’s no more than one alcoholic drink a day for women, no more than two a day for men.

These changes will help beat prehypertension. Even better, they will almost surely lower your risk of having a stroke or heart attack, or developing heart failure, diabetes, kidney disease and some cancers.