A study shows that so-called “good cholesterol” may not be as healthy as previously believed.
The study, published Wednesday in the journal Neurology, claims that high or low levels of high-density lipoprotein, or HDL, could increase dementia risk for older people.
Researchers tracked more than 180,000 California residents through health surveys for about two years starting between 2002 and 2007, then tracked the group using medical records for about nine years on average. The subjects are now an average of 70 years old.
“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,” study author Maria Glymour said in a statement. “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.”
During the course of the study, about 25,000 people developed dementia.
People with the highest levels of HDL cholesterol had a 15 percent higher rate of dementia compared to those in the middle group, the study found. Those with the lowest levels had a 7 percent higher rate of dementia compared to those in the middle group.
The recommended “healthy” HDL amount is 40 mg/dL in blood. Study subjects’ average was about 54 mg/dL.
The study also tracked LDL cholesterol, dubbed “bad cholesterol,” but found that it did not significantly impact dementia rates.
“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 said. “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 dementia as with heart disease and cancer.”
The study released Wednesday follows the results of another released in July which found that having cholesterol levels which fluctuate over time may also increase dementia risk. That study, also published in Neurology, found that people whose cholesterol levels fluctuate the most are at about 19 percent higher risk of dementia.