By Kazem Rahimi
People with diabetes tend to have higher blood pressure levels, which can lead to poor health outcomes such as heart attack and stroke. We know that if you lower the blood pressure of patients with type 2 diabetes you can reduce the risk of cardiovascular disease (CVD), but what hasn't been clear, until now, is whether this applies to all such patients, even those with lower blood pressure levels in the first place. In addition, there has been little evidence available on the impacts of blood pressure-lowering on other factors, such as stroke, kidney disease and diabetic eye disease.
Over the last 12 months, my colleagues and I at The George Institute for Global Health have undertaken a large scale review and analysis of randomized controlled trials of blood pressuring lowering treatment in patients with type 2 diabetes. It is the most comprehensive study of its kind to date, gathering information from 40 trials and 100,354 participants. Across all of the patients, we found that lowering blood pressure reduced the risk of death by any cause by 13%, of cardiovascular events by 11%, of coronary heart disease events by 12% and of stroke by a remarkable 27%. But these reductions differed substantially according to the individual patient's baseline level of blood pressure.
The effect of blood pressure lowering medications on the risk of death and cardiovascular disease was found to be less strong in people with lower baseline blood pressure levels (less than 140mmHg systolic), compared with those who started out with higher blood pressure levels. In other words, everything else being equal, patients with type 2 diabetes who have a low blood pressure to begin with do not benefit as much from the same degree of blood pressure lowering as patients whose blood pressure is higher. But importantly we still found substantial reductions in strokes, diabetic eye disease and albuminuria (too much protein in the urine) even at lower blood pressure levels.
We concluded that diabetic people who start with a blood pressure of 140 or higher will get the most benefit from blood pressure lowering, and for most, the benefits of taking blood pressure medication are likely to outweigh the potential side effects. But in people with systolic blood pressure already below 140 mmHg, careful assessment is needed to work out the net benefit for the patient.
This research provides fundamental evidence about how blood pressure should be treated in people with diabetes, and it is important that guidelines around the world reflect this. Our analyses indicate that many patients with diabetes and low-normal blood pressure levels will still benefit from blood pressure lowering as it will reduce their risks of stroke, diabetic eye disease and early kidney disease. Unfortunately, recent US and EU guideline changes mean that the threshold for commencing blood pressure-lowering treatment in diabetic patients is now 140mmHg, rather than the previous 130mmHg. These changes need to be modified urgently, and guidelines around the world need to consistently reflect the evidence so patients with diabetes are receiving the best possible treatment.
Take home message:
In people with diabetes, blood pressure-lowering medications reduce the risk of stroke and other vascular problems, even when initial blood pressure levels are not very high. Treatment decisions in such people need careful balancing of potential benefits and harms.