Osman Mir, MD

High-density Lipoprotein Subclasses and Risk of Stroke and its Subtypes in Japanese Population:The Circulatory Risk in Communities Study. Stroke. 2013; 44: 327-333

In this issue of Stroke, Chei et al. report a population based study on the correlation of stroke subtypes and HDL subtypes. This was a nested case control study. The authors CIRCS patient’s data and choose, based on CT or MRI, identified 241 patients who had an ischemic or hemorrhagic stroke and as a similar number of controls matched by sex, age, community, serum storage year, and fasting status. They subsequently used HPLC based HDL subtype analysis and did a conditional logistic regression model to find out the relationship between HDL subtypes and different stroke subtypes.

The total HDL level was associated with different HDL level subtypes. BMI was inversely correlated with total HDL levels. Small HDL cholesterol levels were strongly and inversely associated with risk of total stroke, ischemic stroke, particularly lacunar infarction, and hemorrhagic stroke, specifically intraparenchymal hemorrhage even after adjusting for cardiovascular risk factors. There was no such relationship with large HDL cholesterol level. There was moderate relationship with medium HDL molecules.

This is the first study to show that higher levels of small and medium HDL particles were associated with lower risk of ischemic or hemorrhagic stroke after adjustment for known cardiovascular risk factors. The risk of stroke was approximately 90% lower among persons at the highest quartile of small or medium HDL cholesterol levels compared to those who were at the lowest quartile. 

The mechanism by which small or medium HDL particles reduce this risk is unknown and probably complex. One possible mechanism, suggested by authors, is that small and medium HDL cholesterol molecules have more capacity to mobilize cholesterol compared to large HDL molecules. There might be pharmacological or non-pharmacological way either with diet or exercise of boosting your HDL level specifically your small or medium HDL that might lead to lower vascular risk for future vascular events.

This article addresses the discrepancy that just boosting your total HDL level does not necessary lower your vascular event rate. These findings are inline with new evidence coming from cardiology that suggests that simply boosting HDL with statins does not lower the risk of future cardiovascular events.