While high blood sugar is known to be the defining feature of diabetes, it has not been clear whether this contributes independently to heart-disease risk, and therefore raises the risk for healthy people too.
The new study, by a team from the Johns Hopkins Bloomberg School of Public Health and other US institutions, found that Hemoglobin A1c (HbA1c)-a measure of long-term blood glucose level-predicts heart disease risk in both diabetics and non-diabetics.
It supports the value of a low-glycaemic index diet, even before people are diagnosed with diabetes, the group traditionally advised to follow such a regime.
"For non-diabetics, lifestyle modifications, such as increased physical activity, weight loss and eating a healthful, low-glycaemic, index diet rich in fibre, fruit and vegetables, may not only help prevent diabetes, but also reduce the risk of heart disease," said lead author Elizabeth Selvin.
Heart disease is the biggest cause of death in all European countries as well as the US and most developed nations. While the food industry is increasingly developing and promoting foods with a low glycaemic index, most of these are designed to help prevent the onset of type 2 diabetes, a condition that has surged in recent years with the increase in obesity and now affects an estimated 19 million people in the 25 members states of the European Union (over 4 per cent of the population).
The new findings suggest that such foods can also be targeted at those at risk of heart disease.
And in people that already have diabetes, improving blood-glucose control is another way to help lower their high risk of heart disease, in addition to current advice to agressively treat other factors like hypertension and high cholesterol, say the researchers.
For the study, the team used data from the Atherosclerosis Risk in Communities Study (ARIC), a community-based cohort of almost 16,000 people from four states-North Carolina, Mississippi, Maryland and Minnesota.
HbA1c levels were taken from participants during clinical examinations in 1990-1992. They were then tracked for 10-12 years to acquire information on coronary heart disease events, hospitalizations and deaths.
Those people without diabetes but who had 'high normal' HbA1c levels (approximately 5-6 per cent) were at an increased heart disease risk, even after accounting for other factors such as age, cholesterol level, blood pressure, body mass index and smoking, report the researchers in the 12 September issue of Archives of Internal Medicine (165, pp1910-1916).
If these individuals had HbA1c levels of 6 per cent or higher, they almost doubled their heart disease risk compared to people with an HbA1c level below 4.6 per cent.
In diabetics, each 1-percentage-point increase in HbA1c level was associated with a 14 per cent increase in heart disease risk.
The authors note that the current target for 'good' glycaemic control established by the American Diabetes Association is an HbA1c value less than 7 per cent. However, their results suggest that heart disease risk begins to increase at values even below 7 per cent.
Large, on-going clinical trials will in the future determine the effectiveness of blood glucose-lowering medications in decreasing cardiovascular risk in people with type-2 diabetes, said Selvin.
"But our results suggest we should also be concerned about elevated blood sugar levels in non-diabetics as well. An important next step is to investigate strategies for lowering HbA1c in persons without diabetes," she said.
A recent poll of food industry executives by Reuters Business Insight found that 33 per cent expect 'diabetes friendly' foods to be highly profitable by 2009. Low-glycaemic foods are also expected to increase in profitability by 18 per cent between now and 2009.