A recent study looked at the health benefits of type 2 diabetes drugs, comparing drugs that can cause hypoglycemia and those that don’t. The very first sentence of the abstract didn’t give me much hope for what followed. That sentence was: “Different guidelines provide similar, but not identical, therapeutic targets for HbA1c in type 2 diabetes. These targets can also depend from the different pharmacological strategies adopted for intensifying glycemic control.” Did you catch the misprint?
This meta-analysis of 13 clinical trials was looking for differences in various health outcomes over the course of at least two years, comparing successful intensive management to standard care or placebo. Successful intensive management was defined as at least a 0.5% (6 mmol/mol) improvement in hemoglobin A1c (HgbA1c) level. “Intensification” of drug therapy is usually applied to a patient who is not at goal HgbA1c level. Undoubtedly, the benefits of intensification will be greater for those at HgbA1c of 10% than for those at 7.5%. BTW, few large clinical trials include patients over 75 years of age.
For my U.S. readers, note that other countries often specify HgbA1c values as mmol/mol instead of %. And blood sugars are not our usual mg/dl, but instead reported as mmol/l. HbA1c of 7% equals 53 mmol/mol, which would indicate and average blood sugar of 154 mg/dl or 8.6 mmol/l. As another example, HbA1c of 6.5% is 48 mmol/mol, reflecting average blood sugar of 140 mg/dl or 7.8 mmol/l. Are you thoroughly confused yet?
In the general population, lowest levels of mortality are seen at HgbA1c’s around 5 to 5.5% (31 to 36.6 mmol/mol). The average healthy non-diabetic adult hemoglobin A1c is 5% (31 mmol/mol) and translates into an average blood sugar of 100 mg/dl (5.56 mmol/l). This will vary a bit from lab to lab. Most healthy non-diabetics would be under 5.7% (38.8 mmol/mol). In December, 2009, the American Diabetes Association established a hemoglobin A1c criterion for the diagnosis of diabetes: 6.5% (47.5 mmol/mol) or higher. Diagnosis of prediabetes involves hemoglobin A1c in the range of 5.7 to 6.4% (38.8 to 46.5 mmol/mol).
Some expert panels recommend aiming for HgbA1c under 7% (53 mmol/mol), others recommend under 6.5% (48 mmol/mol). A major point of debate between the two guideline goals, is that the lower you set the goal, the greater the risk of drug-induced hypoglycemia, which can be lethal. In the early 1980s, the only drugs we had for diabetes were insulin, sulfonylureas, and metformin. Two of those three can can cause hypoglycemia. Now, a majority of our type 2 diabetes drugs don’t cause hypoglycemia.
The Italian researchers did this meta-analysis as part of their effort to produce diabetes drug treatment guidelines for the Italian population. On to the study at hand…
What Did the Researchers Find?
Improved glycemic (blood sugar) control by intensive attention reduced the major cardiovascular event rate by 10% and reduced renal adverse events by 25% but did not affect overall mortality or eye complications.
Intensified therapy with hypoglycemia-inducing drugs did not reduce overall mortality.
Drugs without potential for causing hypoglycemia were linked to lower risk of major cardiovascular events, kidney adverse events, and overall mortality, for HgbA1c under 7% (53 mmol/mol).
In conclusion, the results of this meta-analysis of RCTs show that in people with T2DM the improvement of glycemic control with drugs not inducing hypoglycemia is associated with a reduction in the risk of long-term chronic vascular complications (major adverse cardiac events and renal adverse events) and all-cause mortality, at least for HbA1c levels above 7%. The reduction of HbA1c below that threshold could have some favorable effects, but there is no available direct evidence in this respect. When the reduction of HbA1c is achieved with drugs inducing hypoglycemia, a progressive reduction of complications and an increase in the risk of severe hypoglycemia is observed. Therefore, the choice of the most adequate HbA1c target for each patient with T2DM should be made considering an appropriate risk/benefit ratio.
I think the researchers were particularly glad to find that intensification of drug therapy can reduce risk of heart attack, stroke, kidney complications, and death; all this without the risk of hypoglycemia that comes with drugs like insulin and sulfonylureas. The lack of a mortality benefit from hypoglycemia-inducing drugs may also be important. The benefits of intensive drug therapy (or lack thereof) depend somewhat on the particular complication you’re trying to avoid, and on baseline HgbA1c. Drug therapy is complicated! I expect these researchers would recommend a treatment HgbA1c goal of <7% rather than <6.5%.
Steve Parker, M.D.
PS: Reduce your need for diabetes drugs by losing excess weight, exercising, and eating low-carb.