Diabetes Distilled: Preventing is better than treating: lowering blood pressure to prevent new-onset type 2 diabetes

It is well established that lowering blood pressure mitigates the future risk of both microvascular and macrovascular disease. However, it is unclear what impact lowering blood pressure has on the incidence of type 2 diabetes; is hypertension a modifiable risk factor for type 2 diabetes?

Previous combined evidence has suggested that each 20 mmHg increase in systolic blood pressure is associated with a 77% increase in the risk of new-onset type 2 diabetes. However, these studies have been of mixed quality, with conflicting results and prone to confounding. It remains unclear whether any beneficial or detrimental effects of blood pressure lowering on the risk of developing type 2 diabetes are due to the reduction in blood pressure itself, or pleiotropic effects of antihypertensive drugs.

Separately, earlier research has demonstrated that thiazide diuretic and beta-blocker use is independently associated with a high risk of new-onset type 2 diabetes (Taylor et al, 2006). In contrast, the use of calcium-channel blockers and ACE inhibitors was not associated with the development of type 2 diabetes. These findings suggest that individuals treated with certain antihypertensive medications might benefit from screening for type 2 diabetes.

A large, well-conducted, individual data meta-analysis, with nearly 150,000 participants, explored the role of blood pressure lowering and the prevention of type 2 diabetes. Individuals were followed-up for a median of 4.5 years. The authors found that a 5 mmHg reduction in systolic blood pressure was associated with an 11% reduction in the risk of developing type 2 diabetes.

Further analysis explored the individual effect of each of the five major classes of antihypertensive.

ACE inhibitors and angiotensin receptor blockers were each associated with a 16% reduction in the risk of type 2 diabetes versus placebo. Calcium-channel blockers had no significant impact on the risk of type 2 diabetes. Beta-blockers and thiazide diuretics were associated with a 48% and 20% increased risk of type 2 diabetes, respectively. These findings are consistent with the research discussed earlier.

There are limitations to this study; new-onset type 2 diabetes was not a pre-specified endpoint in many of the included trials. Furthermore, included trials had different definitions for how type 2 diabetes was diagnosed.

Nevertheless, the authors concluded that these findings could help individualise choice of antihypertensive in those living at increased risk of developing type 2 diabetes (e.g. prediabetes or non-diabetic hyperglycaemia) by prioritising use of ACE inhibitors or angiotensin receptor blockers.

A linked comment does highlight that the absolute risk reduction demonstrated in this meta-analysis was small; however, interventions with modest benefits can have extensive downstream effects in conditions as common as hypertension. Salt reduction for the management of hypertension is a good example of this.

In conclusion, lowering blood pressure does indeed appear to be a modifiable risk factor for type 2 diabetes. However, different antihypertensive agents have varying effects, with most benefits seen with ACE inhibitors and angiotensin receptor blockers. Click here read the study in full.