The number of people who inherit a tendency to develop high levels of cholesterol may be higher than previously thought.

Researchers say the condition, known as familial hypercholesterolemia (FH), may be twice as common in the United States as earlier studies have indicated.

The genetic predisposition can lead to elevated cholesterol levels. The condition is a leading cause of early heart attacks.

The findings were published today in the America Heart Association’s journal Circulation.

"It's more common than we thought and it's important to look for it at a young age. Someone with FH may have no symptoms until there is serious heart disease,” Dr. Sarah de Ferranti, M.P.H., lead author of the study, assistant professor of pediatric cardiology at Harvard Medical School, and director of preventive cardiology at Boston Children’s Hospital, said in a statement.

Read More: When Having Lots of ‘Good’ Cholesterol Isn’t Good »

What the Numbers Say

Previous research done outside the United States showed FH affected about one in every 500 adults.

The study’s researchers, however, took a broad look at figures within the United States.

They pored over statistics from almost 37,000 participants in the 1999-2012 National Health and Nutrition Examination Survey (NHANES). They then projected figures for the 210 million Americans 20 years and older.

They figured that genetically inherited high levels of cholesterol affected closer to one in every 250 U.S. adults. If true, that would mean more than 830,000 Americans have FH.

The researchers said they also found that men and women are affected equally.

In terms of ethnicity, FH affects one in every 211 African-Americans, one in 249 Caucasians, and one in 414 Mexican-Americans.

The researchers said they also discovered FH varies by age and weight.

The data suggest FH becomes more common as people age. One in every 1,557 people in their 20s is affected. One in 118 people is in their 60s.

The condition is also found in one in 172 people who are obese, compared to one in 325 people who are not.

Read More: Half of Latinos Unaware They Have High Cholesterol »

Treating It Early

In the study, researchers focused on high levels of low-density lipoprotein (LDL). That’s considered the “bad” cholesterol because it contributes to plaque build up in arteries.

The biggest danger in FH, the researchers said, is that it can create heart disease before a younger person expects to develop such a disorder.

"If you're born with FH, you have lifelong exposure to high cholesterol, making your heart attack risk similar to someone decades older," de Ferranti said. "If you know that somebody has had an early heart attack in your family, consider asking for everyone to be checked."

If the health problem is caught early, a younger person can be put on statins or other medication. Treatment can reduce LDL levels and the possibility of heart disease.

People with FH should also be warned about contributing factors such as smoking, lack of exercise, and poor diet.

"The fact that FH varies by age and obesity shows that there are other factors at play in raising LDL cholesterol levels in addition to genetics," de Ferranti said.

Researchers plan to study the issue further. They want to better understand the genetic disease and find effective treatments.

A scientific statement by the American Heart Association, published Dec. 1 in Circulation, states FH is "underdiagnosed and undertreated worldwide.”

Read More: Promising Early Results for Cholesterol-Busting PCSK9 Drugs »