Both elevated and low levels of high-density lipoprotein (HDL) cholesterol, commonly known as “good” cholesterol, are associated with a slightly increased risk of dementia in older adults, according to a recent study published in Neurology, the medical journal of the American Academy of Neurology.
This study does not prove that high or low levels of HDL cholesterol cause dementia; it only shows an association.
Background and previous findings
“Previous studies on this topic have been inconclusive, and this study is particularly informative because of the large number of participants and long follow-up,” said study author Maria Glymour, ScD, of Boston University. “This information allowed us to examine the association with dementia across the range of cholesterol levels, and to get accurate estimates even for people with very high or very low cholesterol levels.”
Details of the study
The study involved 184,367 people from the Kaiser Permanente Northern California Health Plan, with an average age of 70, who did not have dementia at the start of the study.
For the research, they completed a survey about their health behaviours and had their cholesterol measured an average of 2.5 times during routine health care visits over the next two years. They were then followed in the Kaiser health care system for an average of nine years using electronic health records. During that time, 25,214 people developed dementia.
Findings on HDL cholesterol levels and dementia risk
The average HDL cholesterol level was 53.7 milligrams per decilitre (mg/dL). Healthy levels are considered to be above 40 mg/dL for men and above 50 mg/dL for women. The participants were divided into five groups based on their HDL cholesterol levels.
People with the highest levels of HDL cholesterol had a 15% higher rate of dementia than those in the middle group. Those with the lowest levels had a 7% higher rate of dementia compared to those in the middle group.
Taking other risk factors into account
These results took into account other factors that could affect the risk of dementia, such as alcohol consumption, high blood pressure, cardiovascular disease and diabetes.
The researchers found only a weak link between low-density lipoprotein, or “bad” cholesterol, and the risk of dementia.
“The increased risk of dementia with both high and low levels of HDL cholesterol was unexpected, but these increases are small and their clinical significance is uncertain,” Glymour said. “In contrast, we found no association between LDL cholesterol and dementia risk in the overall study cohort. Our results add to the evidence that HDL cholesterol has similarly complex associations with dementia as with heart disease and cancer”.
