New research suggests that high-density lipoprotein, or HDL cholesterol, is much more complex than previously thought.

So-called “good” HDL cholesterol may not be as healthy as experts once thought, a new study suggests.

The new study, published Wednesday in Neurology, found that having either high or low levels of high-density lipoprotein, or HDL, cholesterol, may increase the risk of dementia in older adults. It’s more evidence showing that keeping HDL cholesterol within a certain range is important for cardiovascular and brain health.

“The relationship between HDL cholesterol and dementia is more complex than we previously thought," said the study’s lead author, Erin Ferguson, a doctoral student studying epidemiology at the University of California San Francisco. "While the magnitude of this relationship is relatively small, it’s important,”