Low "good" cholesterol doesn't cause heart attacks
To try to isolate the effects of HDL itself, Frikke-Schmidt and her colleagues focused on people with a well-known variant of a gene called LCAT, which lowers HDL levels and occurs in about four percent of the population.
The variant gene is used as a stand-in for low HDL, she noted, but people with the variant don't necessarily have the other risk factors that usually affect HDL levels in the larger population.
In the new study, a 13 percent decrease in HDL relative to average levels in the population was linked to an 18 percent increase in heart attack risk -- if the low HDL was not explained by a gene variant. For people with the variant gene, the same HDL reduction was not linked to any increased risk of heart attack.
The findings add to a growing body of research that's making cardiologists second guess what they've thought for decades, Cannon told Reuters Health.
"It's a total relook at what we thought was gospel," he said.