"What's good for the heart is good for the brain." So is "good cholesterol" good for the brain?

Most of us get our cholesterol levels checked every year or so.  We hope that our "bad cholesterol" (low-density lipoprotein, or LDL) values will be low and our "good cholesterol" (small high-density lipoprotein, or HDL) will be higher.  The right numbers should favor a lower likelihood of stroke or heart attack.  Great.  But what does that mean for our brains -- our cognition and memory?  What does that mean for our susceptibility to Alzheimer's disease?

Remember that the ApoE4 gene variant is the gene most strongly correlated with the "sporadic," or older onset form of Alzheimer's disease.  (The ApoE2 variant seems to be neutral, and ApoE3 actually seems to be protective for Alzheimer's.)  The purpose of the ApoE gene, regardless of the variant, is to provide for a protein that aids in the transport of cholesterol in the blood.  So there's a connection between blood cholesterol and Alzheimer's disease.

That connection may or may not be relevant to new findings reported in the journal Alzheimer's and Dementia by researchers at the USC Keck School of Medicine.  The journal article was entitled "The small HDL particle hypothesis of Alzheimer's disease."  (The research was discussed in this press release.)  The article proposed a new hypothesis regarding Alzheimer's disease, that "small high-density lipoprotein (HDL) particles reduce the risk of Alzheimer's disease by virtue of their capacity to exchange lipids, affecting neuronal membrane composition and vascular and synaptic functions."

So what did they do?  The researchers measured the concentrations of small HDL particles in cerebrospinal fluid (CSF) and the blood of 180 individuals ≥60 years of age.  They found a positive association between small HDL concentrations in CSF and performance in three domains of cognitive function.  The researchers controlled for ApoE4 status, age, sex, and years of education.  They also found a significant correlation between levels of small HDLs in CSF and plasma.  They specifically found that higher HDL values correlated with greater synaptic plasticity, reduced inflammation, more efficient scavaging of oxidized lipids in cerebral blood vessels. Synaptic plasticity is foundational to memory, inflammation is part of the Alzheimer's disease process, and oxidized lipids promote Alzheimer's disease.

Apparently HDL particles come in different sizes, and the small size is most commonly found in the brain.  The researchers claimed credit for being the first to actually count HDL particles in the brain.

The takeaway seems to be that there's a correlation between higher levels of good cholesterol, better memory and cognition, and resistance to Alzheimer's disease.  So this appears to be another reason to track your cholesterol and keep it in recommended limits.  Of course, diet and exercise are your best strategies for this.  As always, more research is required, but the researchers hope this will lead to finding more biomarkers for Alzheimer's and targets for therapies.