Heterogeneity of air pollution effects is related to average temperature
Authors: M. Bobak, A. Roberts
Journal: BMJ (1997)

Influence of cholesterol on survival after stroke Beneficial effects of cholesterol lowering on atherosclerosis may not lessen with ageEditor-In their study of survival after stroke Alexander G Dyker and colleagues showed that serum cholesterol concentration is inversely correlated with degree of disability and all cause mortality in a clinically heterogeneous group of elderly patients with stroke. 1 Interesting though these findings are, they are likely to have only a tenuous connection with the study's stated objective of investigating the association between cholesterol concentration and cerebrovascular disease.As the authors hint in their introduction, the most consistent and direct evidence about the aetiology of stroke may come from postmortem examinations rather than clinical diagnostic groupings, even when supported by the best available brain imaging techniques.The Akita pathology study, to which the authors refer, established a link between high cholesterol concentrations, cortical artery infarction, and widespread atherosclerosis in predominantly larger basal cerebral arteries (1.5-6.0 mm).Low cholesterol concentrations and minimal atherosclerosis were generally associated with cerebral haemorrhage, except for somewhat higher cholesterol concentrations and a substantial incidence of atherosclerosis in those with cerebral haemorrhage aged over 65.Intermediate levels of cholesterol and atherosclerosis were found in cases of penetrating artery infarction.Suspected cardioembolic strokes were classified separately. 2 If these pathophysiological correlates are accepted, the authors need not invoke novel biological mechanisms to explain their results. 3 Rather, if cholesterol is a crude marker for atherosclerosis, their data support the proposition that, in the age group studied, strokes related to atherosclerosis, presumably including some cases of cerebral haemorrhage, have a better prognosis than strokes related to other causes (notably arteriosclerosis). 4 Recent evidence suggests that if the atherosclerotic group can be specifically targeted with lipid (low density lipoprotein cholesterol) lowering drugs before severe damage has occurred, a significant impact on stroke is achievable.Pooled data from four pravastatin atherosclerosis regression trials (coronary or carotid) indicated a reduction in the incidence of stroke of 62% (P = 0.054). 5 There is no a priori reason for assuming that the beneficial effects of cholesterol lowering on atherosclerosis lessen with age, though competing adverse effects might emerge.While the study testifies to the inadequacy of current lipid lowering guidelines in relation to stroke, it cannot legitimately be taken as a contribution to the debate on the efficacy of lipid lowering on the prevention of stroke because lipid lowering (drug) interventions were not part of the design.Therefore, alternative key messages from this paper might be that clinical classifications of stroke provide an unreliable guide to pathogenesis and that the association of cerebral atherosclerosis with stroke improves prognosis in elderly people.Cholesterol's clandestine relation with stroke clearly requires further probing.