A Critical Review of the Evidence Behind Diabetes Guidelines

Blood pressure:

The ADA guidelines suggest a goal BP of <140/90mmHg for most diabetes patients as hypertension is a major risk factor for CVD. The impact of BP lowering on CV events and mortality in diabetes patients was identified in six randomized controlled trials. A reduction in CV death was reported two trials, however in one of these trials, the intensive target was <150/85mmHg rather than <140/90mmHg. Two trials reported a reduction of stroke risk with intensive treatment but no impact on mortality. One study reported fewer CV events in diabetes patients whose diastolic BP was targeted to <80mmHg instead of <90mmHg. Timing of BP medication administration was also investigated; type 2 diabetes patients who took their medications at bedtime rather than in the morning saw a reduction in sleep time BPs and experienced less CV events and mortality. 

Multifactorial interventions:

The impact of treating multiple risk factors was identified in one randomized controlled trial. This approach, which the ADA recommends, led to a significant reduction in CV events, death, and all-cause mortality, compared to conventional therapy.

After reviewing the evidence, the researchers stated that the analysis does support the ADA recommendations for BP and glycemic control as well as Mediterranean diet, however, they noted “several limitations to interpreting the available evidence with regard to the impact of glycemic control on CVD and mortality.”  With regards to aspirin therapy, while the ADA recommends it as secondary prevention in diabetes, the only evidence researchers were able to find was a meta-analysis that showed no benefit. In addition, studies where aspirin was used for primary prevention in high risk diabetes patients failed to show a clinical benefit. The researchers also noted that the evidence for statin use was “both confusing and contradictory” leading them to conclude that both aspirin and statin therapy should be considered on an individual basis “rather than assuming there is a net benefit for all diabetic patients.” The same can be said for antiplatelet therapy, where the risks and benefits of use should be considered for individual patients as some populations may clearly benefit from use (ie, acute coronary syndromes, post-coronary stenting or CABG).

There may be several reasons why the conclusions of this review do not match up with the ADA guidelines, one of which may be that the guidelines rely too much on subgroup and meta-analyses rather than well-conducted randomized controlled trials. “Until more definitive clinical trial results are published, we encourage clinicians to look beyond the summary conclusions and critically review the available evidence,” the authors concluded.

Reference:

Bouchonville, MF; Matani, S; DuBroff, JJ; DuBroff, RJ. Are diabetes guidelines truly evidence based? Diabetes Research and Clinical Practice. 2017. DOI: http://dx.doi.org/10.1016/j.diabres.2017.02.035 (accessed 3/2117).