title: Cholesterol as a Risk Factor for Subarachnoid Hemorrhage: A Systematic Review.
abstract: BACKGROUND
  The role played by total cholesterol (TC) in risk for subarachnoid hemorrhage (SAH) is unclear because studies report both high and low TC each as a risk factor. We performed a systematic review to clarify associations between lipid profile and SAH.
  
  
  METHODS
  Our literature search comprised Pubmed, Scopus, and Cochrane Library databases with no language, publication year, or study type limitations. The Preferred Reporting Items for Systematic reviews and Meta-analyses (PRISMA) checklist guided our reporting. Data forms adapted from the Critical Appraisal Skills Program (CASP), and Cochrane Collaboration guidelines provided a platform for risk-of-bias evaluation. We used a random effects model to calculate pooled estimates and assessed heterogeneity with I2-statistics.
  
  
  RESULTS
  Of the final 21 studies reviewed, 12 were prospective and 9 retrospective. All studies assessed TC, four assessed HDL, and none LDL in risk for SAH. Heterogeneity among all, retrospective, and Asian studies was high (I2 = 79.5%, I2 = 89.0%, and I2 = 84.3%) and considerable in prospective (I2 = 46.0%). We therefore focused on qualitative analysis and found that only two studies had a low risk of bias. According to these studies high TC increases risk for SAH in men, whereas the role of HDL remained unclear.
  
  
  CONCLUSIONS
  The low-risk-of-bias studies suggest that elevated TC levels elevate risk for SAH in men. Due to the high prevalence of hypercholesterolemia, population attributable risk (PAR) of hypercholesterolemia may exceed the PARs of smoking and hypertension in men. Apart from diabetes and obesity, the risk-factor profile of SAH seems to resemble that of other cerebrovascular diseases, at least in men.
authors.affiliation: Department of Public Health, University of Helsinki, P.O. Box 41, FI-00014, Helsinki, Finland.|Department of Neurosurgery, University of Helsinki and Helsinki University Hospital, P.O. Box 266, FI-00029, Helsinki, Finland.
authors.forename: Joni Valdemar
authors.initials: JV
authors.lastname: Lindbohm
authors.affiliation: Department of Public Health, University of Helsinki, P.O. Box 41, FI-00014, Helsinki, Finland.|National Institute for Health and Welfare, P.O. Box 30, FI-00271, Helsinki, Finland.|Institute for Molecular Medicine FIMM, P.O. Box 20, FI-00014, Helsinki, Finland.
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.affiliation: Department of Neurosurgery, University of Helsinki and Helsinki University Hospital, P.O. Box 266, FI-00029, Helsinki, Finland.
authors.forename: Miikka
authors.initials: M
authors.lastname: Korja
mesh_terms: D002784:Cholesterol / Q000378:metabolism*; D006801:Humans; D011446:Prospective Studies; D012189:Retrospective Studies; D012307:Risk Factors; D013345:Subarachnoid Hemorrhage / Q000378:metabolism*
chemical_list: D002784:Cholesterol