Almost 25 million adults in the U.S. have high cholesterol, which puts them at a higher risk of heart disease in the next decade. But a much larger portion have what’s called borderline high cholesterol, an in-between level that’s not quite high, but not quite within the normal range.

Here’s what you need to know about borderline cholesterol.

What is borderline cholesterol?

High cholesterol is defined as having a total cholesterol number of 240 mg/dL or above. Someone has borderline cholesterol when their total cholesterol is between 200 to 239 mg/dL.

“We create these thresholds—which are admittedly somewhat artificial—to classify people so we can understand if we need to do further analysis or assessment to understand their risk for cardiovascular disease,” says Dr. Donald Lloyd-Jones, past president of the American Heart Association and a professor of cardiology and the chair of preventive medicine at Northwestern University Feinberg School of Medicine. There’s some flexibility: Some people may be completely healthy with a total cholesterol level of 235, while others could be at risk at 205. It depends on a person’s other risk factors. But broadly speaking, these thresholds help doctors make decisions about patient care.

People with total cholesterol levels below 200 tend to have a lower risk of developing heart disease, while those over 240 have a higher risk. Those who land from 200 to 239 are somewhere in the middle, Lloyd-Jones says.

Cholesterol levels in this middle category aren’t automatically dangerous, but they do put you at a greater risk of developing high cholesterol, says Dr. Daron Gersch, a family physician with CentraCare Hospital in Long Prairie, Minn. And if you spend enough time in the borderline category, the effects can add up. People who had borderline high cholesterol for 11 to 20 years had twice as high a risk of developing heart disease compared with people who had high cholesterol for 10 years, according to research published in 2015 in .

“The analogy that I use is we are marinating our arteries in these cholesterol particles for our entire lifespan,” Lloyd-Jones says. “The more we marinate, the greater the chance that we form plaques. People who have very high levels for a short period of time are at risk of forming plaques, but even people who have modest levels for a long period of time can form plaques.” Those plaques build up and get inflamed over time, heart attacks and strokes.

The type of cholesterol matters

Total cholesterol levels don’t paint the whole picture. What’s most concerning are your levels of low-density lipoprotein or LDL cholesterol, sometimes called “bad” cholesterol, says Dr. Ann Marie Navar, associate professor of cardiology at UT Southwestern Medical School and co-author of the Circulation study. That’s because LDL is the type of cholesterol that . A is less than 100.

High-density lipoprotein or HDL cholesterol, on the other hand, is sometimes called “good” cholesterol because it removes fats from your blood, Gersch says. A is 60 or higher.

“If your total cholesterol is elevated because of the HDL, then you might not be at higher risk and actually might be somewhat protected,” Gersch says, “so it’s very important to not only get your total cholesterol levels, but to make sure it’s broken down into the good and bad cholesterol.”

That’s why it may be more accurate to look at borderline high LDL cholesterol only, Navar says. LDL cholesterol that’s 160 or higher is considered high, while LDL cholesterol from 130 to 159 is borderline, according to the American Academy of Family Physicians.

This is a rough categorization and not a guarantee of heart problems to come. “LDL-related cholesterol risk is on a continuum—there isn’t a magic number above which you’re at risk and below which you are not,” Navar says. “The higher your LDL is and the longer your LDL is elevated, the more risk you accumulate over time.”

How to lower borderline high cholesterol

After reviewing your blood test results in the context of your medical history, your doctor will recommend the best course of action to get your cholesterol levels into a healthy range for you.

If you have borderline high cholesterol but you’re otherwise healthy and younger than 60, your doctor may recommend lifestyle modifications that can help lower your overall risk of developing heart disease. These might include getting to and maintaining a healthy weight, eating a balanced diet (and scaling back on starches, alcohol, and high-fat foods), , and getting regular exercise.

But if you have borderline high cholesterol—and two or more other risk factors for heart disease—your doctor will likely recommend to keep your heart safe as long as possible, Gersch says. Those risk factors include , diabetes, smoking or exposure to secondhand smoke, being 60 or older, having a family history of heart disease, being sedentary, or carrying extra weight.

When to get your cholesterol tested

If those risk factors sound familiar, you should start . Men without heart disease risk factors can typically wait until 35, and women without these risk factors can wait until 45 to start regular cholesterol testing, Gersch says.

You’ll be retested every four to six years if your test results show your cholesterol is in the healthy range. But you can expect to have bloodwork done more regularly, and as often as , if your levels land you in the borderline or high categories or you have other heart disease risk factors.

Having borderline high cholesterol may mean it’s time to start some preventive measures, but it doesn’t mean a heart attack or stroke is inevitable—and your overall health and risk factors for future heart disease matter more than one specific number in your cholesterol panel.

“Is there really a difference between 199 and 201? No, there’s not,” Lloyd-Jones says. Rather, this is a generalized, population-wide relationship between cholesterol and heart disease risk that’s only one piece of the puzzle on the individual level. “These are kind of arbitrary barriers, but they help initially determine how aggressive and intensive you want to be.”