Cholesterol and subarachnoid hemorrhage: no major link established

Two approaches to examining an uncertain link

The researchers first identified Mendelian randomization studies on blood lipids and intracranial aneurysms or subarachnoid hemorrhage. This approach uses genetic variants associated with lipid traits to examine their relationship with the risk under study. It does not involve administering a treatment.

In parallel, they conducted their own analysis in UK Biobank. It examined genetically predicted LDL cholesterol, HDL cholesterol, total cholesterol, and triglycerides. The analyses accounted for lipid-lowering treatments and also explored nonlinear relationships.

Previous studies were less independent than they appeared

Eight studies met the review criteria, but seven used the same cohort for the events under study. The authors therefore did not conduct a meta-analysis: pooling these results would have raised a data overlap issue.

Despite this largely shared evidence base, the studies did not find a consistent direction of effect across lipid traits. According to the authors, this inconsistency suggests methodological limitations rather than a consistent biological effect.

A negative result, but not proof of no effect

In UK Biobank, the analysis found no evidence of an association between the four genetically predicted lipid traits and subarachnoid hemorrhage. The results remained consistent across different methods and sensitivity analyses, including after accounting for lipid-lowering treatments.

However, the uncertainty intervals remain wide, particularly for HDL. The large sample size alone therefore does not rule out all possible effects.

What this study cannot determine

These results do not challenge the established role of lipids in atherosclerotic diseases: the question examined here is different. Nor do they demonstrate that lipid-lowering treatment prevents, or does not prevent, subarachnoid hemorrhage. Effects of these treatments independent of lipids remain possible.

What we can take away

The data presented do not support a major association between blood lipids and subarachnoid hemorrhage. On their own, they do not justify changing a treatment.