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Data from prospective observational studies indicate that usual levels of blood pressure are directly and continuously related to the risk of stroke. The strength of this association has been substantially underestimated by many previous analyses that have not taken account of the "regression dilution bias;" correction for this increases by about 60% the strength of the association between blood pressure levels and stroke risk. From corrected analyses it is apparent that a difference in usual blood pressure levels of just 9/5 mmHg would ultimately confer about a one-third difference in stroke risk. The associations between blood pressure and stroke risk are of similar size in hypertensives and in normotensives. Moreover, because most strokes occur in normotensives, the stroke avoidance that is likely to be conferred by a downward shift in population blood pressure is actually greater in normotensives than hypertensives. For large populations in which stroke is common, a relatively small change in the average adult blood pressure could have large effects on stroke mortality and morbidity. In China, for example, a decline of 9/5mmHg in the average adult blood pressure might be expected to prevent about 400, 000 deaths from stroke each year; more than three quarters of the deaths prevented would have occurred in normotensive individuals. For individuals, the benefits of blood pressure reduction are likely to be greatest in those at highest risk of stroke. It is possible that blood pressure reduction among either hypertensives or normotensives with a history of cerebrovascular disease could confer particularly worthwhile effects. This hypothesis requires investigation in a large-scale randomised trial. (Hypertens Res 1994; 17: Suppl. I S23-S32)
MacMahon et al. (Sat,) studied this question.