Beta-blockers increase the likelihood of patients with hypertension developing type II diabetes but thiazide diuretics do not, say Dr Todd Gress (department of medicine, Johns Hopkins university school of medicine, Baltimore, US) and colleagues.
They report a study of 12,550 non-diabetic patients in the New England Journal of Medicine (2000;342:905) in which they assessed how many had developed type II diabetes after six years.
Of the study subjects, 3,804 had hypertension. Of this hypertensive group, 569 developed type II diabetes over the six-year period. Those who were taking a thiazide diuretic, an angiotensin converting enzyme (ACE) inhibitor or a calcium channel blocker were at no greater risk of developing type II diabetes than those who were receiving no medication for their hypertension, say the authors.
In contrast, they say, the subjects taking b-blockers were 28 per cent more likely to develop type II diabetes than those on no medication. This was regardless of sociodemographic characteristics, health-related behaviour, family history of diabetes or other coexisting conditions. The increase was also not associated with weight gain or hyperinsulinaemia, they say. The relative odds of developing diabetes in the group taking b-blockers was 1.34, whereas in those taking thiazides it was 0.88.
Dr Gress and colleagues say that type II diabetes was almost 2.5 times more likely to develop in subjects with hypertension as in those with normal blood pressure.
The authors recommend that physicians should not be discouraged from prescribing thiazide diuretics for hypertension in adults because of concerns about increasing the risk of the patient developing diabetes. They also say that, when prescribing b-blockers, the risks should be weighed against their potential for reducing cardiovascular events.
In an accompanying editorial (ibid, p969), Dr James Sowers (State University of New York health science centre) and Dr George Bakris (Rush Presbyterian St Luke's medical centre, Chicago) say that factors not studied, such as changes in the level of aerobic exercise or subtle changes in the cellular actions of insulin, may have contributed to the diabetogenic effect of b-blockers.
They add that ACE inhibitors are "appropriate" as initial agents for lowering blood pressure in patients with type II diabetes because of their "beneficial effects on metabolism".