1. Current evidence does not support blood pressure targets lower than the standard targets for people with raised blood pressure and diabetes
2. Better evidence is needed to guide the choice between targeting intensive or conventional glycaemic control in people with type 2 diabetes but intensive control increases the risk of both mild and severe low blood sugar
Today is World Diabetes Day and there’s a big emphasis on knowing the complications of diabetes and trying to avoid them. Maintaining healthy blood pressure levels and blood sugar levels are important ways to reduce the risk of damage to the heart and blood vessels, kidneys, nerves and eyes. We have new evidence from Cochrane systematic reviews which helps shed some light on which approaches might be best when it comes to setting targets for blood pressure and blood glucose levels.
Blood pressure targets: how low should you go?
When treating high blood pressure (BP), doctors and patients will want to know what levels they’re aiming for. For some time the advice has been that a target of 140/90 mmHg is right for the general population being treated for high blood pressure. The first number, 140 here, is the systolic blood pressure (SBP) and the second, 90, the diastolic blood pressure (DBP) and these are generally considered separately in clinical practice. The National Institute for Health and Care Excellence recommends 140/90 mmHg as the target BP levels for those aged under eighty in their Hypertension Guideline, with no alternative recommendation for people with diabetes.
Other guidelines have recommended lower BP targets for diabetics, including recent European guidelines which recommend a target lower than 140/85mmHg. There was no consistent evidence to recommend a target SBP of below 130 mmHg or DBP below 80 mmHg but there was evidence that a DBP target below 85 mmHg is beneficial for diabetics and the guideline authors say DBP levels of 80 to 85 mmHg are ‘safe and well tolerated’ in all patients. There is a brief summary of the guideline findings, aimed at GPs, here.
An important question is whether lower BP targets for people with diabetes would help reduce complications and deaths. The Cochrane Hypertension Group has now published a systematic review (here) which looked for evidence from randomized controlled trials (RCTs) which could help answer this. They wanted to know how ‘lower’ BP targets (any target less than 130/85 mmHg) compared with ‘standard’ BP targets (less than 140 – 160/90 – 100 mmHg). They found five RCTs with 7314 people, who were followed up for around four and a half years. This included a large trial with over 4,700 people, the ACCORD trial.
What did they find?
- The ACCORD trial is the only trial that has looked at what happens when the target SBP is under 130 mmHg. Trying to achieve a SBP of lower than 120 mmHg instead of lower than 140 mmHg was associated with a small reduction in strokes. 91 people would need to be treated for 4.7 years to prevent one stroke
- This lower SBP target was associated with more serious ‘adverse events’ or side effects/complications of treatment, with one excessive adverse event for every 50 people treated intensively
- There was no benefit associated with a ‘lower’ DBP, evaluated in the remaining four trials
How good was the evidence?
The reviewers say the ACCORD trial provides useful information on SBP, though there are important unanswered questions, such as whether such tight BP control could be useful if put in place early, whether the balance between risks and benefits might be acceptable for people at especially high risk of stroke, and whether a target SBP of lower than 130mmHg might be better than lower than 120mmHg. The evidence on serious adverse events and deaths was low quality, with high risk of bias, and very low quality in the trials looking at DBP. Future research is likely to change the results.
According to the National Diabetes Audit 2011 – 2012, published last month, fewer than half of people with diabetes are meeting blood pressure targets and there are worrying variations between different regions, with many people missing the checks which should help them manage their condition.
Intensive versus conventional blood glucose control for type 2 diabetes (T2D)
The Cochrane Metabolic and Endocrine Disorders Group has updated the review on targeting intensive versus conventional glycaemic control in people with T2D and the review now draws on 28 RCTs with almost 35,000 people.
What did they find?
- No difference between groups in the number of deaths from any cause or from heart disease
- No difference in health-related quality of life
- No difference in the risk of non-fatal stroke from surgery to reconstruct damaged blood vessels
- Intensive control seemed to lower the risk of non-fatal heart attack, lower limb amputation and damage to small blood vessels but increase the risk of serious complications of treatment and both mild and severe low blood sugar (hypoglycaemia)
How good was the evidence?
There was high quality evidence on hypoglycaemia, so we can be confident that intensive glycaemic control increases the risk of both mild and severe low blood sugar. For all other outcomes, the risk of bias was high, so it’s possible that benefits have been overestimated and harms underestimated.
Annie Cooper, a nurse with type 1 diabetes who writes a great blog, has written a powerful piece this week about hypoglycaemic attacks and their consequences for her, in the shape of fear, fits, incontinence and shame. I urge those of you who, like me, are nurses (ok, I haven’t practiced in years but do we ever lose the nurse in us?!) to go and read it. I urge those of you who are diabetic or live or work with people with diabetes to read it. Then I urge everyone else to read it. Many will relate to this, for different reasons, and we should all gain a little more understanding, and maybe a resolve to do something differently, for having done so.
National Clinical Guideline Centre, National Institute for Health and Clinical Excellence. Hypertension: the clinical management of primary hypertension in adults. London: National Clinical Guideline Centre, Royal College of Physicians; 2011. (NICE CG127). [Issued August 2011]. Available from URL: http://guidance.nice.org.uk
Arguedas JA, Leiva V, Wright JM. Blood pressure targets for hypertension in people with diabetes mellitus. Cochrane Database of Systematic Reviews 2013, Issue 10. Art. No.: CD008277. DOI: 10.1002/14651858.CD008277.pub2.
Hemmingsen B, Lund SS, Gluud C, Vaag A, Almdal TP, Hemmingsen C, Wetterslev J. Targeting intensive glycaemic control versus targeting conventional glycaemic control for type 2 diabetes mellitus. Cochrane Database of Systematic Reviews 2013, Issue 11. Art. No.: CD008143. DOI: 10.1002/14651858.CD008143.pub3.
Blog: anniecoops. The thoughts of a nurse with type 1 diabetes. The hardest thing to say. 11th November 2013.