The scientific evidence does not support tight glycemic control as a means to prevent the complications of type 2 diabetes, even though most clinical practice guidelines, quality-of-care measures, quality improvement interventions, and academic and clinical statements unequivocally endorse tight glycemic control for that purpose, according to a report published online Aug. 23 in Circulation: Cardiovascular Quality and Outcomes.
There is an enormous disconnect between the widespread consensus that tight glycemic control is essential on the one hand, and the overwhelming data demonstrating that it doesn’t prevent 10 of the 11 micro- and macrovascular complications that matter most to patients on the other hand. “This consensus and its downstream consequences to practice, policy, and research” must be recalibrated, said Rene Rodriguez-Gutierrez, MD, and Victor M. Montori, MD, both of the Knowledge and Evaluation Research Unit, Division of Endocrinology, Mayo Clinic, Rochester, Minn.
They systematically reviewed the current evidence regarding tight glycemic control (achieving hemoglobin A1c under 7%) published in the five “most impactful” general medical journals (the New England Journal of Medicine, the Lancet, JAMA, the British Medical Journal, and Annals of Internal Medicine) and the two most impactful specialty journals (Diabetes Care and the Journal of the American College of Cardiology) between 2006 and 2015. This included 328 research articles, 16 sets of treatment guidelines, 11 meta-analyses, and five large, randomized clinical trials and their extension studies, as well as relevant letters, commentaries, and editorials. They also reviewed national guidelines and standards of care published in all languages during the study period.
The investigators focused on the effect of tight glycemic control, as opposed to looser control, on 11 outcomes most important to patients: end-stage renal disease or the need for dialysis, renal death, blindness, clinical neuropathy, microalbuminuria, retinal photocoagulation, all-cause mortality, cardiovascular mortality, nonfatal MI, fatal and nonfatal stroke, and peripheral vascular events or amputations.
Regarding the microvascular complications, good evidence shows that tight glycemic control has no significant impact on the risk of end-stage renal disease, renal death, blindness, or clinical neuropathy, and that there is no threshold HbA1c effect on risk. Moreover, the incidence of such complications is very low (less than 6%). Nevertheless, “practice guidelines and published statements offer a consistent and confident consensus, with 100% of the guidelines and 77%-100% of academic and clinical statements in favor of tight glycemic control to prevent microvascular complications,” according to Dr. Rodriguez-Gutierrez and Dr. Montori (Circ Cardiovasc Qual Outcomes. 2016 Aug 23;9:00-00. doi: 10.1161/CIRCOUTCOMES.116.002901).
Regarding the macrovascular complications, the evidence consistently shows that tight glycemic control exerts no significant effect on all-cause or cardiovascular mortality or on fatal or nonfatal stroke. The putative protective effect reported on amputations is “imprecise,” as it is based on very few such events. The only protective effect of tight glycemic control in this category of complications is that it reduces the risk of nonfatal MI by 15%.
Since the publication of the ACCORD trial, which clearly questioned the ability of tight glycemic control to prevent macrovascular complications, the consensus on this point has “withered.” At present, 64%-79% of published statements now express “uncertainty and skepticism” that tight glycemic control is essential. Yet two sets of guidelines – the American Diabetes Association standards published in 2003 and 2004 – did so.
The study findings indicate that despite good evidence to the contrary, the unsupported “consensus” on tight glycemic control drives most guidelines and quality-of-care interventions. It also underlies “the Food and Drug Administration policy to approve diabetes mellitus drugs only on the basis of their antihyperglycemic effect, without requiring evidence of reduction in the risk of complications,” the investigators said.
“This consensus is also driving studies such as the National Institutes of Health–funded GRADE trial comparing antihyperglycemic drugs on their ability to reduce HbA1c, rather than to reduce the risk of diabetes complications,” they added.
The narrow focus on tight glycemic control has undercut research on other possible interventions to prevent these complications. There are zero trials currently under way assessing treatment possibilities other than drugs that reduce hyperglycemia, and there are zero evidence-based therapies either mentioned in guidelines or routinely prescribed to patients for preventing these complications, Dr. Rodriguez-Gutierrez and Dr. Montori wrote.
“A careful and thoughtful recalibration” is needed. “Today, patients with type 2 diabetes, at least in some parts of the world, seem to live longer lives with fewer complications. The evidence summarized here requires us to explore factors other than tight glycemic control to explain this improvement and better address the diabetes epidemic,” they noted.
This study was supported by the National Center for Advancing Translational Sciences, a component of the National Institutes of Health. Dr. Rodriguez-Gutierrez and Dr. Montori reported having no relevant financial disclosures.