Hypertension and coronary artery disease in non-insulin dependent diabetes--cause and effect?

There is a log-linear increase in the risk of coronary heart disease with elevation of levels of blood pressure. Allowing for the phenomenon of regression dilution bias, this corresponds to around a 20 to 25% increase in risk for each 5 to 6 mm Hg elevation in usual diastolic blood pressure. In diabetic subjects, a similar relationship occurs, but of somewhat lesser degree. Recent overviews of therapy suggest that in nondiabetics, reducing blood pressure reverses around 50% of the excess coronary heart disease risk, but this has not yet been conclusively shown in patients with diabetes. The reduction in risk with therapy is a prerequisite to defining the antecedent as a causal influence on outcome, but it is as likely that the incomplete reversibility of excess risk represents other pathways of connection between hypertension and coronary heart disease as a consequent of iatrogenic effects of current treatments. Several alternative mechanisms are outlined, and the suggestion is made that only in the context of randomized controlled studies could the possible benefits on coronary heart disease of agents influencing such mechanisms be assessed.