Evidence from observational studies
A systematic review of 45 observational studies of about 450,000 people over 16 years identified no clear relation between plasma total cholesterol and the occurrence of any stroke (after adjusting for age, gender, ethnicity, blood pressure and history of cardiac disease), suggesting that cholesterol was not a risk factor for any stroke (Prospective Studies Collaboration, 1995). A more recent, but smaller metaanalysis of eight observational studies of 24,343 women found that increasing plasma cholesterol was a significant independent risk factor for death due to any stroke among black women less than 55 years of age (Horenstein et al., 2002).
It is possible that the overall association between total cholesterol and all stroke dilutes real associations between cholesterol and pathological subtypes of stroke, and between cholesterol fractions and pathological and aetiological subtypes of stroke.
Subtypes of stroke
There is a weak (positive) association between increasing plasma cholesterol concentrations and increasing risk of ischaemic stroke which is partially offset by a weaker (negative) association between decreasing plasma cholesterol concentrations and increasing risk of haemorrhagic stroke (Iso et al., 1989; Eastern Stroke and Coronary Heart Disease Collaborative Research Group, 1998; Koren-Morag et al., 2002; Asia Pacific Cohort Studies Collaboration, 2003).
Fractions of cholesterol
Increasing low-density lipoprotein-cholesterol (LDL-cholesterol) concentrations of 1.03 mmol/l (40 mg/dl) have been associated independently with a 14% (95% confidence interval (CI): 0–26%) increase in odds of ischaemic stroke or transient ischaemic attack (TIA) (Koran-Morag et al., 2002).