It's generally considered a good thing to have elevated levels of HDL cholesterol, also commonly referred to as "good" cholesterol. But new research indicates that when those HDL levels climb too high, dementia could be an unwanted side effect.
Cholesterol is a tricky, sticky thing. Too much of it overall in our circulatory system can lead to plaques that create blockages, which restrict blood flow. Once those plaques are formed, they can't be removed – although new research suggests that the element manganese might be effective in doing just that.
Yet, conventional wisdom has said that having higher levels of one type of cholesterol known as high-density lipoprotein (HDL) in your body is good for preventing this buildup. That's because HDL cholesterol functions to soak up bad cholesterol in the bloodstream and deliver it to the liver where it can be processed and eliminated. Still, a study released last year called into question the function of HDL cholesterol in preventing heart attacks, and found that its effects on reducing cardiovascular disease only applied in white populations.
Now, a study from Monash University has concluded that very high levels of HDL can actually be quite bad for us. The researchers analyzed data from the Aspirin in Reducing Events in the Elderly (ASPREE) trial, which has tracked the health of over 19,000 elderly people from the US and Australia since 2010. The primary aim of the study was to see how daily aspirin use affected participants, but the study also provided medical data that can be useful in other analyses. Also, at the start of the study, none of the participants had dementia, physical disabilities, cardiovascular disease, or life-threatening illnesses, so it's a useful group to study as changes in health develop among the cohort.
The researchers found that during a period of 6.3 years, individuals with HDL cholesterol levels over 80 mg/dl were 27% more likely to develop dementia than those with healthy HDL levels, which are considered to be in the 40-60 mg/dl range.
When those same HDL levels were observed in participants over 75 years old, the rate of dementia climbed to 42%. To put the findings in perspective, the researchers found just over 2,700 people who had extremely high HDL levels at the start of the study. Of those, 38 participants under the age of 75 developed dementia, as did 101 of those beyond age 75.
The researchers say that the high values they saw in the people chosen for the study were likely caused by metabolic disorders rather than anything to do with their diets.
“While we know HDL cholesterol is important for cardiovascular health, this study suggests that we need further research to understand the role of very high HDL cholesterol in the context of brain health,” said first author and Monash University School of Public Health and Preventive Medicine senior research fellow Monira Hussain. “It may be beneficial to consider very high HDL cholesterol levels in prediction algorithms for dementia risk.”
Hussain also said that further research is needed to investigate the link between extremely high HDL levels and the development of dementia.
The research has been published in the journal The Lancet Regional Health - Western Pacific.
Source: Monash University