High good and low bad cholesterol are not just good for the heart but also the brain, suggests new research published in JAMA Neurology.
Study leader Bruce Reed, a professor of neurology at the University of California (UC) Davis, and associate director of its Alzheimer's Disease Center, says:
"Our study shows that both higher levels of HDL - good - and lower levels of LDL - bad - cholesterol in the bloodstream are associated with lower levels of amyloid plaque deposits in the brain."
He explains that while we already have long-standing evidence of raised cholesterol linked to a higher risk of developing Alzheimer's, their study is the first to link it to amyloid plaques in the brains of living people.
Prof. Reed says:
"Unhealthy patterns of cholesterol could be directly causing the higher levels of amyloid known to contribute to Alzheimer's, in the same way that such patterns promote heart disease."
The study participants were 74 men and women aged 70 and over who were attending the Alzheimer's Disease Center, stroke clinics, and community senior facilities.
The group included three people with mild dementia, 38 with mild cognitive impairment, and 33 who were cognitively normal.
All the participants had fasting blood tests and underwent brain PET scans where amyloid plaques were highlighted using a radioactive tracer that binds to them.
When they analyzed the results of the blood tests and brain scans, the researchers found that higher levels of "bad" cholesterol (LDL) and lower levels of "good" cholesterol (HDL) were linked to more amyloid plaques in the brain.
The findings were independent of age or presence of the E4 variant of the ApoE gene, which has been linked to some forms of Alzheimer's.
Control cholesterol to keep brain healthy later in life
In the US, a level of 60 milligrams (mg) of HDL cholesterol per deciliter (dL) of blood or higher is considered protective against heart disease, and for LDL cholesterol, a level of 100 mg/dL is considered optimal, with 70 mg/dL or lower recommended for people at very high risk of heart disease.
Study co-author Charles DeCarli, also a professor of neurology at UC Davis and director of its Alzheimer's Disease Center, says their findings are a "wake-up call" in that not only can people improve their chances of keeping their brains healthy later in life by controlling their blood pressure, but also by controlling their cholesterol:
"If you have an LDL above 100 or an HDL that is less than 40, even if you're taking a statin drug, you want to make sure that you are getting those numbers into alignment. You have to get the HDL up and the LDL down."
Guidelines issued recently from expert bodies in the US have suggested LDL targets should be abandoned where heart health is concerned.
But Prof. Reed believes their findings point to an exception to the old adage that says what is good for the heart is good for the brain:
"This study provides a reason to certainly continue cholesterol treatment in people who are developing memory loss regardless of concerns regarding their cardiovascular health."
"It also suggests a method of lowering amyloid levels in people who are middle aged, when such build-up is just starting. If modifying cholesterol levels in the brain early in life turns out to reduce amyloid deposits late in life, we could potentially make a significant difference in reducing the prevalence of Alzheimer's, a goal of an enormous amount of research and drug development effort."
According to the American Heart Association, factors that can be controlled through changes in lifestyle, such as diet, weight, physical activity and exposure to tobacco smoke, all affect people's cholesterol levels.