This “Good” Health Metric Was Just Linked with Elevated Alzheimer’s Risk, Research Finds

Updated: Jan. 08, 2024

It's classically associated with heart health, but a new Australian study finds a mysterious connection that science may need to further probe.

When we think of cholesterol, we tend to associate the concept of it with our hearts and circulatory systems. When a healthcare provider checks your cholesterol levels, they will analyze your cardiovascular disease risk based on the total cholesterol, HDL (high-density lipoprotein), LDL (low-density lipoprotein), and triglyceride numbers.

Generally, HDL, which is often called the “good” cholesterol, is considered protective of arteries at a higher level, while elevated LDL is considered to be problematic and potentially artery-clogging.

A November 2023 study in a regional edition of the prestigious peer-reviewed medical journal, The Lancet, suggests that the “good” HDL could potentially spell bad news for older adults who want to prevent cognitive decline or Alzheimer’s. Researchers from top universities in Australia were guided by several studies which had shown that very high levels of HDL were associated with several conditions that can worsen an individual’s quality of life, including macular degeneration of the eyes, sepsis and bone fractures, and that HDL levels of this nature could even shorten lifespan.

In addition, while higher levels of HDL cholesterol have been shown to reduce heart-related issues, some research had suggested that high levels of HDL may be associated with dementia in people aged 47 to 68 years. The researchers in this study wanted to see if the same rang true for those most highly at risk for cognitive decline, namely people over the age of 65. This later-onset dementia, they theorized, might be different than the earlier-onset type.

More than 18,000 participants in the study over the age of 65 were evaluated for their cholesterol levels and took a mental acuity test. Then, they were reevaluated every two years. If their performance fell below a certain threshold on the test or they were diagnosed in some other way with cognitive decline, that was documented as dementia.

The researchers discovered that high HDL levels were associated with all forms of dementia in middle-aged and elderly participants. However, those who were 75 years and older saw the greatest risk in relation to high HDL levels.

If you’re curious about the HDL numbers that caused concern, the research suggested the “danger zone” for HDL cholesterol appeared to be levels of 80 milligrams deciliter (mg/dL) or greater, resulting in a 27% higher risk for all age groups. (View our cholesterol chart by age to see where experts suggest your levels should fall.) With an adjusted model that took into account different mitigating factors like gender, economic status and lifestyle choices such as smoking and alcohol consumption and exercise habits, the outlook was even worse for those over 75, who saw an estimated 42% increase in dementia risk with the higher HDL readings.

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So what gives? Should people who are trying to protect their hearts and their memories while they age eschew cholesterol readings entirely? The researchers emphasize that the study has limitations, and the mechanism causing the association between cholesterol and cognitive decline is unclear. “The possibility also exists that increased dementia and very high HDL are both consequences of a separate and unrelated pathology,” they surmised. Plus, other studies have found a protective effect from higher HDL levels. In addition, heavy alcohol use can cause higher HDL levels, but can certainly have negative effects on aging brains, and that nuance might not have been captured in the study.

Overall, a healthy diet low in saturated fat and a regular pattern of exercise is still recommended to optimize cholesterol numbers. The people who exhibited the greatest cognitive decline in the study were less physically active and more frail in general; they also tended to skew female.

The people with HDL levels over 80 mg/dL generally had healthier hearts, were more physically active, and had lower rates of high blood pressure, diabetes, and kidney disease—all of which have been tied to better brain health in later years.