MI Seems to Be a Risk Factor for Diabetes

BOSTON, Aug. 24 -- Myocardial infarction more than doubles the risk of new-onset diabetes and leads to a 15-fold increased risk of impaired fasting glucose, according to a study of more than 8,000 MI patients.

During a mean follow-up of 3.2 years post-MI, 3.7% of patients developed diabetes, compared with 0.8% to 1.6% for historical cohort populations with no history of MI, Dariush Mozaffarian, M.D., of Harvard, and colleagues, reported in the Aug. 25 issue of The Lancet.

Additionally, they found, 27.5% of patients developed impaired fasting glucose compared with 1.8% of historical cohorts.

"Our results indicate that myocardial infarction could be a prediabetes risk equivalent," the authors wrote. "Smoking cessation, prevention of weight gain, and consumption of typical Mediterranean foods might lower this risk, which emphasizes the need for guidance on diet and other lifestyle factors for patients who have had a myocardial infarction."

Although diabetes confers a well documented risk of coronary disease and MI, less is known about the impact of MI on subsequent diabetes risk. Dr. Mozaffarian and colleagues retrospectively examined the issue in 8,291 patients who had had an MI within the previous three months and were free of diabetes before the infarction. The patients were participants in the Italian GISSI Prevention trial.

New-onset diabetes was defined as use of diabetes medication or a fasting glucose of 7 mmol/L or greater. Impaired fasting glucose was defined as a blood glucose level of 6.1 mmol/L or greater but less than 7, but it was also calculated on the basis of a lower blood glucose threshold of 5.6 mmol/L.

During follow up, 998 patients (12%) developed diabetes, and 2,514 (33%) developed diabetes or impaired fasting glucose, increasing to 62% using the lower cutoff threshold.

In contrast, contemporary population-based cohort studies of middle-aged white adults have shown diabetes rates of 0.8% to 1.6%, the authors stated. The incidence of new-onset impaired fasting glucose has been 1.8%, using a blood glucose range of 5.6 to 7.0 mmol/L.

New-onset diabetes and impaired fasting glucose increased the mortality risk in MI patients. As compared with patients who had a fasting glucose of less than 5.6 mmol/L, those with a glucose level of 5.6 to 6.05 mmol/L had a 10% greater mortality during follow-up.

A glucose level of 6.1 to 7 mmol/L increased the mortality risk by 15%, and development of frank diabetes raised the mortality risk by 44% (P<0.05 for trend).

In a multivariate analysis, independent predictors of diabetes and impaired fasting glucose were:

• Older age (hazard ratio 1.07, P<0.001)
• Higher body mass index (HR 1.09, P<0.001)
• Hypertension (HR 1.22, P=0.003)
• Current smoking (HR 1.60, P<0.001)
• Use of beta-blockers (HR 1.27, P<0.001)
• Use of lipid-lowering agents (HR 0.78, P=0.001)
• Higher Mediterranean diet score (HR 0.65, P=0.002)

Independent predictors of diabetes but not IGF were inability to exercise (HR 2.43), use of diuretics (HR 1.15), and wine consumption exceeding 1 L per day (HR 1.45).

Further adjustment for baseline clinical variables revealed additional predictors of diabetes risk after MI: BMI gain during follow-up (HR 1.17), higher triglycerides (HR 1.61), lower HDL (HR 1.46), higher leukocyte count (HR 1.23), and higher consumption of butter and other oils (HR 1.26).

"These findings indicate that, just as diabetes can be considered a coronary heart disease risk-equivalent, acute myocardial infarction should potentially be considered a prediabetes risk-equivalent," the authors said.

Lifestyle modification could play a major role in reducing diabetes risk after MI, they continued. Obesity (as reflected by BMI), smoking, and lack of physical activity are major, modifiable contributors to diabetes risk.

In a commentary on the study, Lionel H. Opie, M.D., of the University of Cape Town, South Africa, said the findings "further tie the knot between myocardial infarction and hyperglycemia-each causes the other."

Offering a possible explanation for the link between MI and diabetes, he noted that blood glucose values of less than 5.6 mmol/L have prognostic value for diabetes.

"A reasonable hypothesis would be that the previous acute myocardial infarction was associated with an undetected modest, but definite tendency towards prediabetes at the time of the attack," said Dr. Opie.

Dr. Opie declared no conflict of interest.