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A new genetic study published in the journal Science suggests that contrary to the conventional wisdom, high levels of good cholesterol aren't necessarily heart-protective for everyone.

"Twenty years ago, if you had high bad cholesterol and high good cholesterol, doctors said don’t worry about it -- one offsets the other," Dr. Scott Wright, a cardiologist at the Mayo Clinic, who wasn't involved in the study, told The Huffington Post."I never really bought that, and time has proven my skepticism to be correct. You can have a heart attack despite having a high level of good cholesterol."

Doctors have long assumed that high levels of good cholesterol were intrinsically heart-protective, in recent years companies have focused on developing medications that boost these levels, with decidedly underwhelming results. Instead, according to this latest research, some people with naturally high good cholesterol due to a genetic mutation are at an increased risk of heart disease.

"It challenges our conventional wisdom about whether 'good' cholesterol is protecting people from heart disease or not," study author Adam Butterworth, a researcher at the University of Cambridge, told BBC. Drugs "trying to raise HDL may not be that useful," he said.

The difference between good and bad cholesterol

In general, high levels of bad (LDL) cholesterol leads to build up of the fatty, wax-like substance throughout the body, and good (HDL) cholesterol picks up those LDL deposits and clears them out of the body via the digestive tract. You would think that a stronger waste-management system (read: high levels of good cholesterol) would mean the body is running efficiently and you're healthier, but the new Science study shows that in some cases, that's not true.

The study analyzed 1,000 people with a SCARB1 gene mutation, which leads to naturally elevated good cholesterol levels, and found -- surprisingly -- that those individuals were at an 80 precent increased risk for heart disease.

Of course, this doesn't mean that everyone with high levels of good cholesterol is at an increased risk. The SCARB1 gene mutation is rare, only affecting 1 out of every 1,700 people. For the rest of the naturally high, good cholesterol folks, who don't have the SCARB1 gene mutation, good cholesterol could still offer them some degree of protection against heart disease.

Nearly all of the study participants with the SCARB1 gene mutation were of Ashkenazi Jewish descent (a group that's already at risk for other genetically linked conditions, including Gaucher disease, Parkinson's disease and breast and ovarian cancers). Still, it's important to note that SCARB1 gene mutations aren't limited to Ashkenzai Jews.

You can improve your health, even if you have 'bad' genes

"It's never too early to start with a good family health history," Dr. Charis Eng, a cancer geneticist at the Cleveland Clinic, previously told HuffPost. She advised sitting down with the family member who knows your extended family's health the best, and using that information to draw up family health blueprint (which you should update periodically).

And if you have both high good cholesterol and a family history of heart disease, which kills more than 600,000 Americans every year, you should talk to your health care provider about lowering your risk, according to Wright.

"Never assume you’re completely protected just because your good cholesterol is high," he said. "You always need to be paying attention to the other risks and living a healthy lifestyle to try to reduce your risk of heart disease."

Perhaps most importantly, the study shouldn't be interpreted as demonizing good cholesterol. The classic nutrition advice still holds: Quit smoking, try to maintain a healthy weight, exercise and focus on eating a healthful diet of lean proteins, lots of produce and healthy fats.

"Anything we do with diet and exercise to raise or improve our good cholesterol is healthy and not harmful," Wright said, who tells his own patients to get their weight in a healthy range and practice interval training to boost their good cholesterol and protect against heart disease.