New research examines the data of almost 100,000 participants and finds that excessively low levels of low-density lipoprotein (LDL) cholesterol increase the risk of hemorrhagic stroke.

The internet abounds with articles and scientific studies that warn health-care consumers of the perils of high cholesterol levels. Whether it is LDL cholesterol—also known as "bad" cholesterol—raising heart disease and early death risk or high levels of "good" cholesterol increasing the risk of heart attacks and cardiovascular death, excessive cholesterol seems to link inextricably to poor health.

However, could it be the case that excessively low cholesterol also harms cardiovascular health? Some researchers have recently argued that this is the case. For instance, a study that Medical News Today reported on earlier this year found that very low levels of bad cholesterol raise the risk of hemorrhagic, or bleeding, stroke in women over the age of 45 years.

Now, a new, large-scale study appearing in the journal Neurology confirms the idea that too little LDL cholesterol may increase the risk of bleeding stroke in both men and women. Xiang Gao, associate professor of nutritional sciences and director of the Nutritional Epidemiology Lab at Pennsylvania State University (Penn State) in State College, is the senior author of the study.

Cholesterol in moderation may be key

"For our study, we wanted to expand the scope of knowledge in this area by investigating the issue prospectively in a large cohort with multiple LDL cholesterol measurements to capture variation over time," explains first author Chaoran Ma, who is a nutritional sciences graduate student at Penn State.

Specifically, Gao and team examined 96,043 participants who did not have a history of stroke, heart attack, or cancer at the start of the study. The researchers measured the participants' LDL cholesterol at baseline and then every year for 9 years.

Using data from the participants' medical records, the scientists examined the correlation between LDL cholesterol levels and the risk of hemorrhagic stroke, adjusting for potential confounders including age, sex, blood pressure, and other medication.

They found that people whose LDL cholesterol levels were below 70 milligrams per deciliter (mg/dL) had a significantly higher risk of hemorrhagic stroke than those with LDL cholesterol levels greater than or equal to 70 mg/dL. The likelihood of having a bleeding stroke was 169% higher among the participants whose LDL cholesterol levels were below 50 mg/dL than among those whose levels were 70–99 mg/dL. For cholesterol levels between 70 and 99 mg/dL, stroke risk stayed the same among participants.

"Traditionally, an LDL cholesterol level of more than 100 mg/dL had been considered as optimal for the general population and lower in individuals at elevated risk of heart disease," explains Gao. "We observed that the risk of hemorrhagic stroke increased in individuals with LDL cholesterol levels below 70 mg/dL. This observation, if confirmed, has important implications for treatment targets," he continues.

"As is true with many things in nutrition, moderation and balance [are] key when deciding the optimal target level of LDL cholesterol. You can't go to either extreme—too high or too low."

—Xiang Gao

"And, if you're at a high risk for hemorrhagic stroke due to family history or risk factors like high blood pressure and heavy alcohol drinking, you may want to be extra careful about LDL cholesterol levels," continues the senior author.

Ma comments on the strengths of the study, saying, "The results were based on a large community-based study, which is an advantage because it focused on healthy people in a nonclinical setting."