November 1, 2023
Many experts tout the benefits of having high levels of high-density lipoprotein, or HDL, the so-called “good” cholesterol. But too much HDL may have a downside: an increased risk of Alzheimer’s disease.
A new study found that older adults with either very high or very low levels of HDL had a higher risk of Alzheimer’s disease and related forms of dementia than their peers with normal HDL readings. The findings, published in the journal Neurology, underscore the importance of keeping cholesterol levels in a healthy range for optimal brain health.
“The elevation in dementia risk with both high and low levels of HDL cholesterol was unexpected,” said study author Maria Glymour of Boston University. “Previous studies on this topic have been inconclusive.” But, she added, “these increases are small,” and “their clinical significance is uncertain.”
The study showed only an association between HDL levels and dementia risk and cannot prove cause and effect. But the study was large, involving 184,367 older men and women in northern California whose average age was 70. None had dementia or other serious memory problems at the start of the study.
Participants filled out health and lifestyle questionnaires and had their cholesterol levels measured several times during the first few years. Researchers then reviewed their medical records over the next nine years or so. During that time, slightly more than 25,000 had developed Alzheimer’s disease or other forms of dementia.
The average HDL cholesterol level among those in the study was 53.7 milligrams per deciliter of blood. Healthy HDL levels are considered to be above 40 for men and above 50 for women.
The researchers divided the participants into five groups, according to their HDL levels. Those with the highest HDL levels — 65 or higher — had a 15 percent higher risk of dementia compared to those in the middle group. Those with the lowest HDL levels — 11 to 41 — had a 7 percent higher risk of dementia than those in the middle group.
Researchers found only a slight association between elevated levels of LDL, the so-called “bad” cholesterol, and increased dementia risk. But other studies have found that having high LDL or high total cholesterol in midlife are linked to an increased risk of Alzheimer’s disease.
Experts advise that people aim to keep total cholesterol levels under 200, with less than 100 mg/dL of the “bad” LDL kind. Men and women should aim for HDL cholesterol levels around 60. Other studies suggest that extremely high levels of HDL, of 90 to 100 or higher, may have adverse health effects.
Regular exercise, and especially aerobic activities like walking, dancing or running, are thought to boost levels of “good” HDL cholesterol. Other studies have shown that regular exercise may likewise reduce the risk of developing Alzheimer’s later in life. Exercise also improves cardiovascular function, including blood flow to the brain. In addition, a heart-healthy Mediterranean diet, rich in fish, nuts and healthy oils like olive oil, is also recommended to keep the brain healthy into old age.
By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Eric Schmidt, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University.
Source: Erin L. Ferguson, MPH; Scott C. Zimmerman; Chen Jiang; et al: “Low- and High-Density Lipoprotein Cholesterol and Dementia Risk Over 17 Years of Follow-up Among Members of a Large Health Care Plan.” Neurology, October 4, 2023
