Does treatment of hypertension explain the decline in mortality from stroke?

Mortality from stroke has been declining in New Zealand since 1950 and at an accelerating rate since the early 1970s. Hypertension is the single most important risk factor for stroke. The temporal association between the recent decline in mortality and an increase in the proportion of patients with hypertension detected and treated led to the assumption of a cause and effect relation. Data from studies of the prevalence of blood pressure carried out in the community and from therapeutic trials of the treatment of hypertension were used to estimate the proportion of the decline in mortality from stroke that could be accounted for by increased treatment of hypertension during 1973-82 in New Zealand. Treatment of hypertension was estimated to account for roughly 10% of the observed reduction in deaths from stroke. Greater understanding of the reasons for the decline in mortality from stroke is required.