March 8 (HealthDay News) -- Even "high normal" fasting glucose levels increase the risk of hospitalization for congestive heart failure, according to a study that looked at data on more than 31,500 patients in two international trials.

Researchers concluded that even small increases in fasting glucose levels increased the risk of congestive heart failure in patients with diabetes and in patients whose blood sugar levels were in the normal range.

The average follow-up time for the patients in the study was 2.4 years. An increase of 1 millimole per liter of blood (mmol/L) in blood glucose level increased the risk of hospitalization for congestive heart failure or cardiovascular death by nine percent for all patients, by five percent for those with diabetes, and by three percent for those without diabetes.

"Even in the normal range, our results indicate that elevated blood glucose is associated with the risk of heart failure," study lead author Dr. Claes Held, associate professor of cardiology at the Karolinska Institute in Stockholm, Sweden, said in a prepared statement.

"You can look at blood glucose much like blood pressure or cholesterol. Even if you have normal blood glucose, there is a gradual increase in risk wherever you start on the scale. If the blood sugar is 'high normal,' there is a higher risk than those with 'low normal' fasting blood glucose levels," Held said.

The study is published in the new issue of the journal Circulation.

The researchers noted there are a number of possible reasons for the link between higher blood glucose levels and an increased risk of congestive heart failure.

"Individuals with disturbances in their glucose regulation usually have more coronary artery disease, which is a well known underlying risk factor for heart failure. That is a strong explanation for our findings but the others are more speculative and hypothetical," Held said.

The study's main sponsor was drug company Boehringer-Ingelheim Pharma GmbH.