dementia

Both High and Low HDL Cholesterol Tied to Increased Risk of Dementia

A new study found that having either high or low levels of high-density lipoprotein cholesterol, or “good” cholesterol, is tied to a small increased risk of dementia in older adults.

Older adults who have high or low levels of high-density lipoprotein (HDL) cholesterol, known as the “good” cholesterol, may have a small increased risk of developing dementia, according to a new study by a School of Public Health researcher. 

Published in the journal Neurology, the study found that people with the highest levels of HDL cholesterol had a 15 percent higher rate of dementia and those with the lowest levels had a 7 percent higher rate of dementia, compared to older adults in the middle range of cholesterol levels.  

“Previous studies on this topic have been inconclusive and this study is especially informative because of the large number of participants and long follow-up,” says study corresponding author Maria Glymour, chair and professor of epidemiology. “This information allowed us to study the links with dementia across the range of cholesterol levels and achieve precise estimates even for people with cholesterol levels that are quite high or quite low.” 

For the study, Glymour and colleagues from The University of California San Francisco and Kaiser Permanente analyzed survey data among 184,367 people enrolled in the Kaiser Permanente Northern California health plan with an average age of 70 who did not have dementia. The participants answered questions on their health behaviors and had their cholesterol levels measured during routine healthcare visits an average of 2.5 times in the following two years. They were then followed within the Kaiser healthcare system for an average of nine years. During that time, 25,214 people developed dementia. 

The average HDL cholesterol level was 53.7 milligrams per deciliter (mg/dL). Healthy levels are considered to be above 40 mg/dL for males and above 50 mg/dL for females. Participants were divided into five groups based on their HDL cholesterol levels. 

These results took into account other factors that could affect the risk of dementia, such as alcohol use, high blood pressure, cardiovascular disease and diabetes. 

The researchers found only a slight association between low-density lipoprotein, or “bad” cholesterol, and the risk of dementia. 

“The elevation in dementia risk with both high and low levels of HDL cholesterol was unexpected, but these increases are small, and their clinical significance is uncertain,” Glymour says. “In contrast, we found no association between LDL cholesterol and dementia risk in the overall study cohort. Our results add to evidence that HDL cholesterol has similarly complex associations with heart disease and cancer.”