People who have type 2 diabetes and experience large variations in blood sugar levels are at a higher risk of heart disease, according to a new study published in the journal Diabetes, Obesity & Metabolism.
The research team, which was led by Gang Hu, MD, of the Pennington Biomedical Research Center in Baton Rouge, Louisiana, remarked on the wide use of the HbA1c test, which reflects a person’s blood sugar control over a period of two to three months, while noting that “emerging evidence” seems to suggest that fluctuations in blood sugar levels “may be a better predictor of diabetic complications” than a single HbA1c test taken on one visit to the doctor. However, they said, because no studies have investigated the possible relationship between HbA1c variability and cardiovascular disease, they set out “to investigate between visit-to-visit HbA1c variability and the risk of cardiovascular disease in patients with type 2 diabetes.”
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The researchers used anonymous electronic health record data collected on patients with type 2 diabetes between January 1, 2013, and April 30, 2018. The subjects had at least one year’s worth of data available for analysis and had to have undergone regular checkups during the study period. To be included in the study, patients had to have been given at least four HbA1c tests in the first two years after being diagnosed with diabetes. Those who already had some form of cardiovascular disease were omitted. The final number of subjects was 29,260 (17,329 white; 11,868 African American).
The researchers discovered some interesting things about the patients who showed greater blood sugar level variability from visit to visit. First, they tended to be younger and to have higher blood pressure levels and a higher BMI (body-mass index, which is a measure of overweight and obesity). They also were more likely to be smokers and less likely to use blood pressure- or glucose-lowering medications. During the follow-up periods, which ranged from approximately three to four years, a little over 6,000 patients developed some form of cardiovascular disease. It became clear to the researchers that, as they put it, “the positive association between HbA1c variability markers and the risk of cardiovascular disease was consistent in patients of different age, races, sexes, BMI, baseline HbA1c levels, patients that had never smoked, and patients receiving and not receiving lipid-lowering and antihypertensive agents.” In other words, people who showed greater fluctuations in HbA1c levels were more likely to develop cardiovascular disease.
In a way, the results were not unexpected because, as the researchers pointed out, earlier studies had either suggested or reported comparable conclusions. For example, a meta-analysis published in 2015 had ascertained that HbA1c variability was associated with blood vessel complications, while other reports found a link between blood sugar variability and the risk of cardiovascular disease even in patients who did not have diabetes. The authors summed up their findings by writing, “The present study found positive associations between different HbA1c variability markers and the risk of coronary heart disease, stroke, and cardiovascular disease in patients with type 2 diabetes. The associations were all significant when using three different markers for HbA1c variability.”
As to why wide swings in HbA1c levels raise the risk of heart disease, the authors said, “The underlying mechanism…is unclear. It’s possible that episodes of severely low blood sugar may be the connection.” They noted, however, that wide blood sugar variability has been associated with “poor adherence to treatment, poor self-efficacy in diabetes management, complications with co-morbid conditions, and poor quality of life with a lack of support.” In other words, these patients are either not managing their diabetes well or they have an inadequate help network, although the researchers pointed out that their data did not include socioeconomic variables so they could not explore these factors.
What was clear, however, was the importance of monitoring and watching for variations in blood sugar levels and taking measures to counteract them. According to Dr. Hu, “We recommend that patients and their doctors implement therapies that can reduce wide swings in blood sugar levels and the associated episodes of severe low blood sugar. Our findings suggest that measuring the swings in blood hemoglobin A1C levels over a specific time — six months to a year, for example — could serve as a supplemental blood sugar target.”
Want to learn more about protecting your heart? Read “Be Heart Smart: Know Your Numbers,” “Does Diabetes Hurt Your Heart?” “Fight Off Heart Disease With These Five Heart-Healthy Foods” and “Lower Your Risk of Heart Disease.”
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