Better Blood Sugar Tracking: A Benefit for Heart Health?

Continuous Glucose Monitors May Help People Better Manage Diabetes

The high blood sugar levels that characterize diabetes are bad news for blood vessels. Elevated blood sugar can damage artery walls, making them more likely to narrow and stiffen; it also makes the blood stickier and more likely to clot. Having diabetes more than doubles your risk of heart disease.

Checking blood sugar has long required people to prick their fingers and squeeze out a drop of blood. But growing numbers of people with diabetes are now using continuous glucose monitors (CGMs), which are small devices placed on your arm or belly with sensors inserted just under the skin. The devices measure a proxy for blood sugar every few minutes and transmit the readings to your smartphone or a portable monitor.


CGMs are already widely used by people with type 1 diabetes, the less common but more severe form of diabetes. Recent research suggests that people with type 2 diabetes -- who account for more than 90% of diabetes cases -- may also benefit from the technology. Meanwhile, television ads (including one during this year's Super Bowl) have boosted awareness of the devices among the general public.

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"Many of my patients with type 2 diabetes are asking me about CGM devices," says Dr. Anna Goldman, an endocrinologist who specializes in diabetes at Harvard-affiliated Brigham and Women's Hospital. Currently, Medicare covers CGMs for people who inject insulin at least three times a day or use an insulin pump to control their blood sugar. Previously, people had to show they were checking their blood sugar at least four times daily, but that requirement was eliminated in July 2021, removing one of the barriers to getting a CGM, says Dr. Goldman.

Earlier this year, two studies in JAMA found that for people with type 2 diabetes who take insulin, using a CGM led to better blood sugar control than traditional monitoring. One of the studies, which used real-world patient data, also documented fewer episodes of dangerously low or high blood sugar values among CGM users.


Using a CGM can be very helpful by providing immediate feedback about how diet and exercise affects blood sugar. For example, people can see how bigger portions or poor food choices cause their blood sugar to rise -- and how exercise helps lower blood sugar. "I've had patients tell me, 'Thank you for asking me to use this device; it really helped me change my habits,'" says Dr. Osama Hamdy, an associate professor of medicine at Harvard Medical School and director of the obesity clinical program at the Joslin Diabetes Center. Research suggests that the more frequently people test their blood sugar, the more weight they lose, he adds.

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One widely used test to assess diabetes control, hemoglobin A1c (referred to as A1c) reveals a person's average blood sugar levels over about three months. But A1c values can be misleading, says Dr. Hamdy. "You can have frequent episodes of very high and very low blood sugar and your average will still be fine. But that doesn't mean your blood sugar is well controlled," he explains.

CGM readouts also show your blood sugar trends and tell you the percentage of time that your blood sugar is in a "good control" range (70 to 180 milligrams per deciliter for non-fasting levels). The higher your "time in range," the better. Growing evidence suggests that frequent blood sugar fluctuations -- known as glycemic variability -- challenge your cardiovascular system. Sugar (glucose) is the fuel that provides energy for all the cells in your body. "Imagine you're driving a car and it's not getting a constant supply of fuel. Sometimes there's a lot, but sometimes there's not enough. That's hard on the motor," says Dr. Hamdy.

Another advantage of CGMs: they can be programmed to send an alert when your blood sugar is too high or too low, and they can send that data in real-time to family or friends.


External CGM sensors (which are about the size of a quarter but thicker) need to be replaced every 10 to 14 days. An implantable CGM that lasts 90 days is also available, and one company is developing a version that lasts up to six months. As the technology improves and the costs decrease, the use of these devices will continue to expand, says Dr. Hamdy. "Within 10 years, everyone with diabetes will have a continuous glucose monitor," he predicts.


This article was originally published on Harvard Heart Letter (TNS).


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