Acute Myocardial Infarction: A Prediabetes Risk Equivalent?

August 28, 2007 — Physicians should consider acute myocardial infarction (AMI) to be a prediabetes risk equivalent, authors of a new study say.[1] Dr Dariush Mozaffarian (Harvard Medical School, Boston, MA) and colleagues report that compared with people who have not had an AMI, post-AMI patients have a significantly higher risk of developing diabetes or impaired fasting glucose.
"We know that diabetes is a risk factor for CAD [coronary artery disease]," senior author on the study, Dr Roberto Marchioli (Consorzio Mario Negri Sud, Chieta, Italy) told heartwire. "What was not well known is that after MI [myocardial infarction], a lot of patients are at risk of developing diabetes or disturbance of glycemic metabolism. And this is what we saw in our paper."
The results of their study appear in the August 25, 2007 issue of The Lancet.
Over a five-year period, Mozaffarian and colleagues tracked new-onset diabetes or the development of impaired fasting glucose (IFG) in a cohort of more than 8000 non-diabetic men and women who had experienced a recent AMI at baseline. Study participants were originally followed as part of the GISSI-Prevenzione trial, one of the first studies to establish the benefits of a Mediterranean diet, high in n-3 polyunsaturated fatty acids. The investigators also collected information on body mass index (BMI), cardiovascular risk factors, diet, lifestyle, and medication use at baseline and over the follow-up period.
Over a mean of 3.2 years (and a total of 26 795 person-years), 33% of the cohort developed diabetes or IFG, a number that rose to 62% when a lower cut-off for IFG was used (5.6 mmol/L). The annual incidence rate among the GISSI study group was 27.5% for IFG, using the 5.6 mmol/L cut-off, and 3.7% for diabetes. By way of comparison, Mozaffarian et al point out that studies in the general population indicate that middle-aged adults face an annual rate of developing IFG of 1.8% and of developing diabetes, 0.8-1.6%.
The authors identified older age, high blood pressure, use of beta-blockers or diuretics, higher BMI, smoking, and low Mediterranean diet score as independent risk factors for diabetes or IFG development. By contrast, use of lipid-lowering drugs, high intake of foods characteristic of Mediterranean diets, and increased physical activity levels seemed to be protective.
To heartwire, Marchioli hypothesized that lifestyle habits were likely "the most important determinant of diseased metabolism."
"We found that increased BMI was associated with the risk of developing diabetes and impaired fasting glucose and we also saw that weight gain after MI was associated with increased disease," he said. "Similarly we saw that patients who had bad dietary habits with a lower intake of fruit, vegetables, fish, and olive oil, had a higher risk of developing diabetes. The same was seen in patients who had the lowest physical activity. So there was a kind of cumulative indication saying that if you don't have good lifestyle habits, you are at high risk of becoming obese and developing diabetes."
The authors say their findings should prompt a rethinking of cardiovascular disease (CVD) and diabetes as both risk factors, and end points. "Just as diabetes can be considered a coronary heart disease risk-equivalent, acute myocardial infarction should potentially be considered a prediabetes risk-equivalent," they write.
But they are also careful to emphasize that they do not believe AMI itself increases the risk of diabetes; rather, some common pathways likely increase the risk of both MI and subsequent diabetes, including an increased likelihood of metabolic dysfunction. Indeed, in an accompanying editorial, Dr Lionel H Opie (University of Cape Town, South Africa), points out that the notion of AMI as an acute stress reaction precipitated in part by metabolic changes dates back more than 40 years.[2] If stress mediates hyperglycemia, he notes, it is "logical" to expect that AMI survivors might also be at risk of developing diabetes. Opie hypothesizes that a tendency towards prediabetes at the time of AMI might get the necessary boost towards overt diabetes or IFG over ensuing years in the form of bad lifestyle habits, or even use of beta blockers and diuretics, both known to affect insulin sensitivity.
Both Opie and the study authors highlight the apparent benefits, in this setting, of the Mediterranean diet rich in fruit, vegetables and n-3 polyunsaturated fatty acids, but low in saturated fats and refined carbohydrates. Opie speculates that the combination of these foods may have a "double benefit": protecting against both cardiovascular events and new diabetes. Likewise, Marchioli and colleagues emphasize that counseling postinfarct patients about the importance of diet and lifestyle should not be overlooked, not only for secondary CVD prevention, but also to prevent the development of diabetes.
"I think that this study should be useful to remind people, starting with the physician, that lifestyle changes should always be assessed in the physician's office," Marchioli told heartwire. "Patients believe their physicians and if the physician emphasizes the importance of diet, physical activity and stopping smoking, that could be the most important message from our study."
Sources
Mozaffarian D, Marfisi RM, Levantesi G, et al. Incidence of new-onset diabetes and impaired fasting glucose in patients with recent myocardial infarction and the effect of clinical and lifestyle risk factors. Lancet 2007;370:667-675.
Opie LH. Acute myocardial infarction and diabetes. Lancet 2007;370:634-635.