More than 14 million Americans have type 2 diabetes, a condition that puts them at risk for blindness, heart disease, and stroke. Diabetes develops when the body cannot properly use insulin, a hormone that allows blood sugar (glucose) to enter cells and use it for energy.

A fasting plasma glucose test (FPG) is one of a number of ways to test for diabetes. In this blood test, doctors measure the amount of glucose in the blood after eight hours of fasting. A measure of 126 milligrams per deciliter (mg/dL [7.0 mmol/L]) or more of glucose indicates a diagnosis of diabetes. Blood glucose levels between 100 and 126 mg/dL (5.6-7.0 mmol/L) are defined as pre-diabetes, which means blood glucose levels that are higher than normal but not high enough to be diagnosed as diabetes.

People with fasting blood glucose levels of 100 mg/dL (5.6 mmol/L) or less are considered to have normal blood glucose levels. But are there varying degrees of normal? In other words, does a person with blood glucose levels on the low side of normal have less risk of developing type 2 diabetes than someone on the high side of normal?

In an article published in the October 6, 2005 New England Journal of Medicine , researchers report that young men with higher blood glucose levels within the normal range are significantly more likely to develop type 2 diabetes than young men with fasting blood glucose levels in the lower range of normal. In addition, traditional risk factors for type 2 diabetes such as high body mass index (BMI) or high triglyceride levels amplify that risk.

About the Study

The researchers collected data from the Metabolic, Lifestyle, and Nutrition Assessment in Young Adults (MELANY) study, which was designed to investigate risk factors for common diseases in young adults. The study participants answered detailed questions about their nutrition, lifestyle, medical history, and demographic characteristics. Their height and weight were measured and they underwent a complete physical exam. In addition, all study participants submitted blood samples that were used to measure fasting plasma glucose levels as well as triglyceride levels.

For this study, researchers looked at information collected on 13,163 men, aged 26-45 years, who had normal fasting plasma glucose levels (100 mg/dl or less) at the beginning of the study. They categorized the men into five groups, or quintiles, based on their fasting plasma glucose levels. Over an average follow up of about six years, they recorded all newly diagnosed cases of type 2 diabetes.

They then analyzed whether men with higher fasting blood glucose levels within the normal range had an increased risk of developing type 2 diabetes compared to men whose fasting blood glucose levels were on the lower end of normal.

The Findings

Overall, 208 men were diagnosed with type 2 diabetes during the study.

Men with fasting plasma glucose levels in the third, fourth, and fifth quintiles (average FPG levels of 88.6, 92.5, and 96.9 mg/dl, respectively) had a significantly higher risk of developing type 2 diabetes than men with average fasting plasma glucose levels in the first quintile (average FPG level of 76.4 mg/dl). This was true even after the researchers took relevant risk factors such as age, family history of diabetes, triglyceride levels, BMI, physical activity, and smoking status into account. Men with the highest average fasting plasma glucose levels (96.9 mg/dl) were 2.84 times as likely to develop type 2 diabetes as men with the lowest average levels (76.4 mg/dl).

Higher serum triglyceride levels and BMIs increased the risk associated with high-normal FPG levels. Men with high-normal FPG levels (91–99 mg/dl) and serum triglyceride levels ≥ 150 mg/dl were 8.23 times more likely to develop type 2 diabetes than men with FPG levels ≤ 86 mg/dl and triglyceride levels < 150 mg/dl.

Obese men (BMI ≥ 30) with high-normal FPG levels (91–99 mg/dl) were 8.29 times as likely to develop type 2 diabetes as men with a BMI < 25 and FPG levels ≤ 86 mg/dl.

How Does This Affect You?

This study found that even within a range of fasting plasma glucose levels considered “normal,” men with higher FPG levels were significantly more likely to develop type 2 diabetes than men with lower FPG levels. Still, the overall risk was fairly small: only 208 of the 13,163 men with normal FPG levels developed diabetes.

As this study showed, blood glucose levels do not exist in a vacuum. A person with normal blood glucose levels is still at risk for type 2 diabetes if they are overweight (high BMI) or have a high triglyceride level.

In many individuals this diabetic triple threat – high-normal FPG, high BMI and elevated triglycerides – can respond to simple lifestyle interventions, the most important of which is regular exercise.