Background: Previous research has suggested that thiazide diuretics and beta-blockers may promote the development of type 2 diabetes mellitus. However, the results of these studies have been inconsistent, and many studies have been limited by inadequate data on outcomes and by potential confounding. Methods: We conducted a prospective study of 12,550 adults 45 to 64 years old who did not have diabetes. An extensive health evaluation conducted at base line included assessment of medication use and measurement of blood pressure with a random-zero sphygmomanometer. The incidence of new cases of diabetes was assessed after three years and after six years by measurement of serum glucose concentrations while the subjects were fasting. Results: After simultaneous adjustment for age, sex, race, education, adiposity, family history with respect to diabetes, physical-activity level, other health-related behavior, and coexisting illnesses, subjects with hypertension who were taking thiazide diuretics were not at greater risk for the subsequent development of diabetes than were subjects with hypertension who were not receiving any antihypertensive therapy (relative hazard, 0.91; 95 percent confidence interval, 0.73 to 1.13). Likewise, subjects who were taking angiotensin-converting-enzyme inhibitors and calcium-channel antagonists were not at greater risk than those not taking any medication. In contrast, subjects with hypertension who were taking beta-blockers had a 28 percent higher risk of subsequent diabetes (relative hazard, 1.28; 95 percent confidence interval, 1.04 to 1.57). Conclusions: Concern about the risk of diabetes should not discourage physicians from prescribing thiazide diuretics to nondiabetic adults who have hypertension. The use of beta-blockers appears to increase the risk of diabetes, but this adverse effect must be weighed against the proven benefits of beta-blockers in reducing the risk of cardiovascular events. (C) 2000, Massachusetts Medical Society.
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