Blood Sugar Predicts Cardiac Mortality

Summarized by Robert W. Griffith, MD
June 17, 2005

Introduction

There are over 17 million diabetics in the USA, and this number is rapidly increasing. It's alarming to hear, however, that this may be just the tip of an iceberg - what's called the 'dysglycemic iceberg'. Dysglycemic means that the blood sugar - fasting or after a meal - is too high. Two publications in the Annals of Internal Medicine have explored the risks of the rest of the iceberg, namely those associated with elevated blood sugars which don't amount to diabetes.

The important blood sugar levels are those that are measured with the subject fasting, and those measured 2 hours after a standard glucose drink. However, there's a substance in the blood called glycosylated hemoglobin, known as hemoglobin A1c, or HbA1c, that accurately represents the usual daily fasting and 2-hour levels for the past 2 to 3 months. It's a cheap test, and can be done at any time of day. In diabetics, the HbA1c level is closely linked to the development of eye, kidney and nerve complications; and decreasing the level (by treating the diabetes) reduces the risk of these complications.

The first study

Johns Hopkins scientists pooled and analyzed the results from 10 studies¹ (i.e. it was a meta-analysis) involving 7500 type 2 diabetic patients. They found that a one-percentage point increase in HbA1c was linked to an 18% increased risk of heart attack or stroke, and a 28% increase in the risk of peripheral vascular disease. So someone with an HbA1c of 9% has a 1.54-times greater risk of a heart attack than someone with an HbA1c level of 6% (3-percentage point increase = 18% x 3 increased risk).

The scientists also reviewed 3 studies of type 1 diabetics and found similar results, although they were not statistically significant as each had relatively few patients.

The second study

This study² used information from a large 6-year study of people aged 45 to 80 living in Norfolk, UK. Over 25,000 men and women, only some of whom had diabetes, were enrolled. HbA1c was measured, along with known risk factors for cardiovascular disease, such as systolic blood pressure, cholesterol level, body mass index (BMI), girth, smoking, and previous heart attack or stroke. The investigators found that there was a 21% increase in cardiovascular events (i.e. heart attack, stroke) for every 1% increase in HbA1c over 5%. And there was an increased risk of death-from-any-cause of 24% for men and 28% for women for each 1% increase in HbA1c.

What do these studies tell us?

They prove that HbA1c is an independent risk factor for cardiovascular events, regardless of whether diabetes has been diagnosed or not. This means that HbA1c testing should be added to the other established tests for increased cardiovascular disease risk, such as blood pressure, cholesterol level, BMI, etc.

Studies are now being done to see if reducing the HbA1c level (by lifestyle changes and/or medication) will reduce the risk of cardiovascular disease, in both diabetic and non-diabetic people.

An obvious question people will ask: "What's the 'normal' HbA1c level?" The answer usually given is 4% to 7% (this means 4-7% of the total blood hemoglobin level). But HbA1c is a bit like LDL-cholesterol - we aren't sure just how low is too low. The risk increase in the second study described above started in the 5% to 6% range, so one might say that this study showed that 6% was abnormal. Who knows what future studies will show to be the ideal lower limit for HbA1c?

Source

• Glycosylated hemoglobin: finally ready for prime time as a cardiovascular risk factor. HC. Gerstein, Editorial. Ann Intern Med, 2004, vol. 141, pp. 475--476

Footnotes
1. Meta-analysis: Glycosylated hemoglobin and cardiovascular disease in diabetes mellitus. E. Selvin, S. Marinopoulos, G. Berkenblit,  et al., Ann Intern Med, 2004, vol. 141, pp. 421--431
2. Association of hemoglobin A1c with cardiovascular disease and mortality in adults: The European prospective investigation into cancer in Norfolk. K-T.  Klew, N. Wareham, S. Bingham,  et al., Ann Intern Med, 2004, vol. 141, pp. 413--420

Related Links
Close Attention to Health Goals Benefits People with Diabetes
How Diabetics Should Avoid Serious Cardiac Events
Statins Reduce the Risk of Coronary Artery Disease in Type 2 Diabetics

Please take a moment to give us your comments. For questions about Health matters you may check our "Questions & Answers" Portal and Service.