About one out of 10 Americans has diabetes and many of them, following their doctor’s orders, check their blood sugar every day (some multiple times a day). According to the U.S. Centers for Disease Control (CDC), “Regular blood sugar monitoring is the most important thing you can do to manage type 1 or type 2 diabetes.” It enables you to see what makes your sugar levels go up or down, such as diet, medicine, and exercise (or lack of exercise), and this knowledge can help prevent diabetes complications.
But checking the blood with a test strip or a glucose meter only shows a user’s blood sugar level at the time of the check. Diabetes experts also rely on what’s known as the HbA1c test, now often called the A1C test, which was developed in the 1970s but didn’t come into regular use until well after that. It was only in 2010 that the American Diabetes Association recommended the HbA1c test to diagnose diabetes and prediabetes.
The HbA1c test measures what percentage of hemoglobin proteins in the blood are glycated (coated with sugar). The reason it’s so useful is because it provides an overview of average blood sugar levels for the past two to three months — information that can be valuable in tailoring treatment to help prevent diabetes complications. Recently, however, researchers in Israel published a study in the journal Diabetes/Metabolism Research and Reviews that indicates that the HbA1c test can tell health care providers even more than that. It appears that adults who have a higher variability in their HbA1c levels over a period of five years have a greater mortality risk.
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The research team, which was led by Avivit Cahn, MD, of Hadassah Hebrew University, used data collected from 2012 to 2016 by the Israeli National Diabetes Registry. The study population consisted of 293,314 individuals ages 35 to 89 who were listed at least four times in Israel’s National Diabetes Registry. The male-female split was about 50-50 and the median age was 68. About half (54.8%) had diabetes for more than 10 years, and one out of four was using insulin. The median HbA1c was 7%. HbA1c values were collected each year, and data on deaths came from Israel’s national population register. The researchers excluded people whose HbA1c was under 4% or those who had type 1 diabetes. They then grouped the subjects into clusters depending on whether their HbA1c was increasing, was stable, or was decreasing. Mortality risk was calculated in subgroups defined by age (35 to 54, 55 to 69, 70 to 89) and by HbA1c at the end of the study.
The researchers determined that people with diabetes whose blood sugar levels fluctuated over the five-year period had an increased risk of death compared to those whose levels remained steady. This finding applied to people in all three age subgroups. The researchers also concluded that the HbA1c trend also predicted mortality. Subjects with a decreasing HbA1c trend had a greater mortality risk, an association that was found in all age groups in patients with an HbA1c under 7% at the end of the study period. Among patients above 70, however, an increasing HBA1C trend also indicated a greater risk of death. “These data,” said Dr. Cahn, “highlight the importance of maintaining glycemic stability throughout the years and encourage physicians to consider the longstanding glycemic burden of their patients when evaluating their prognosis. HbA1c variability and trend are important determinants of mortality risk and should be considered when adjusting glycemic targets.”
The Israeli study followed a British study published in 2018 that reported both low and high levels of blood sugar control, as measured by HbA1c, were associated with an increased mortality risk, and the level of variability appeared to be an important factor, At that time, the researchers speculated that variability “might be an important factor in understanding mortality risk in older people with diabetes.” The work of Dr. Cahn and his team has now determined that variability is in fact important.
Want to learn more about managing blood glucose? See our “Blood Sugar Chart,” then read “What Is a Normal Blood Sugar Level?” and “Strike the Spike II: How to Manage High Blood Glucose After Meals.”