Do You Really Need a Continuous Glucose Monitor (CGM)?

Janet Tiberian Author
By Janet Tiberian, MA, MPH, CHES
August 16, 2023
female using glucose monitor while sitting in front of weights

Do You Really Need A CGM?

A future version of the Apple Watch may include the ability to measure blood sugar without a finger prick. While this is good news for people with diabetes who must regularly test their blood sugar, it’s also a response to the rising trend of Americans keeping tabs on their blood glucose levels.

Monitoring blood sugar has been part of diabetes management for decades, but it’s recently become associated with weight management and high-end athletics, too. In fact, many people are embracing a new kind of blood glucose monitoring technology, whether they really need it or not.

How Our Bodies Use Glucose

Our bodies typically manage our blood glucose levels. When we eat, our pancreas releases insulin, which escorts blood sugar into our cells. Once there, glucose powers cell functions. In people with type 1 diabetes, the pancreas produces little or no insulin, and they must take insulin for the body to function normally. In type 2 diabetes, the pancreas produces insulin, but the cells in the body don’t respond to the insulin and have trouble absorbing glucose.

People with diabetes need to know their blood sugar levels to manage them. High blood sugar can cause you to feel sick and can lead to serious health problems. Chronically high blood sugar can damage the kidneys, cardiovascular system and eyes.

Testing Blood Glucose Levels

There are multiple ways to test blood sugar levels, including blood tests that look at levels over time and technology that constantly monitors glucose. This level of testing hasn’t always been available. Since the mid-1800s, doctors and researchers have been trying to quantify and monitor blood sugar levels. Most early tests could only be performed by physicians.

But in the 1970s and 1980s, researchers developed the first home blood glucose meters. These meters allowed people with diabetes to prick their fingers, place a drop of blood on a glucose strip which the meter would read and measure. This process often repeated six or seven times a day. The technology has improved and now requires less blood and uses smaller devices.

In 1999, the FDA approved the first continuous glucose monitor. Over the last two decades, the technology has improved and become more widely available. Originally, designed for people with type 1 diabetes, CGMs are now routinely prescribed for patients with type 2 as well.

How Does A Continuous Glucose Monitor Work?

While there are multiple brands of CGMs available, they largely work the same. In most cases, a small sensor is inserted under the skin, usually in the abdomen or on the back of a thigh or upper arm. The sensor or probe is in contact with the interstitial fluid underneath the skin and measures blood glucose there. It can estimate your blood glucose levels based on the sugar in your interstitial fluids.

A transmitter connects to the sensor and wirelessly sends data to either a smart phone, reader or other device like an insulin pump.

The device measures regularly or continuously as the name suggests, anywhere from every minute to every 15 minutes.

The biggest differences between CGM models are:

  1. Whether the sensor is placed on the skin or is implanted
  2. How often the sensor has to be replaced
  3. How long it takes the CGM to warm up
  4. How you adjust the program settings

Since CGMs measure sugar levels in interstitial fluid, they aren’t quite as timely as other measuring devices like glucose meters which look at blood glucose levels directly. CGMs accurate but reflect your glucose levels up to 15 minutes before the test. This can affect the timeliness of a treatment if you have diabetes.

But where other meters measure one event, CGMs measure continuously and can track trends, determine if glucose levels are going up or down and at what rate, which makes managing diabetes easier and more predictable.

For instance, if you’re have type-one diabetes and your sugar levels are trending high, you may need to take insulin to lower your blood sugar. If you have type-two diabetes and your blood sugar is continuously lower, your physician may need to adjust your medications.

A CGM device plus subscription plan can range from $100 to $400. Most CGM companies require a prescription from a doctor, which may be covered by insurance and/or Medicare. There may be other costs for people with diabetes too, including supplies and shipping.

Continuous Glucose Monitoring Without Diabetes

Although developed for people with type one diabetes, CGM technology has been approved for use in people with type 2 diabetes and is often used in people with pre-diabetes (people with pre-diabetes have elevated blood sugar levels that can progress to type 2 diabetes if nothing changes). In this case, it is used as an educational tool to demonstrate the effect of different food types or exercise on blood sugar levels.

Lately, however, CGMs have been adopted by a different population: High-end athletes and others trying to track and ultimately hack their metabolism. The makers of these devices are also targeting people without diabetes can be complicated.

Expanding on CGM for athletes, fluctuations in glucose level during and after exercise can impact performance and recovery. In a number of studies, researchers have used CGMs to monitor glucose levels in elite athletes. For example, ultramarathoners, cyclists and adventure racers have been outfitted with CGMs to look at carbohydrate intake and exercise impact.

While the studies have noted variations in blood glucose levels especially in the days following an extreme exercise event, researchers suggest CGMs can help understand their need for carbohydrates during recovery. It’s important to note that these results and conclusions are in extreme elite athletes, not in normal athletes. In sub-elite athletes, a couple of studies have concluded that CGMs may be helpful to monitor recovery after an intense exercise event, especially to moderate carbohydrate intake.

But these studies are small and do not yet support large adoption of CGMs by most people, despite efforts by CGM makers to advertise such use. One challenge for users may be interpretation. As studies have shown, glucose levels are extremely variable in individuals based on genetics, age and other factors. For example, researchers found some subjects were more sensitive than others to carbohydrates. But that doesn’t mean those athletes are spending lots of time out of a healthy range.

In non-athletes without diabetes, there’s less evidence to support CGM use. Multiple studies using CGMs in normal people generally show that the body is doing what the body is supposed to do, managing spikes in glucose levels. For example, in one study involving 12 different health centers with non-diabetic patients wearing sensors for 10 days, the median time non-diabetic subjects spent with blood glucose levels above normal was a paltry 2 percent.

Some studies have shown that CGMs can help motivate overweight and obese adults to move more. Other trials are looking at CGMs use for helping people with type 2 diabetes or pre-diabetes to lose weight.

The skinny? Right now, there is little evidence to support the use of CGMs in healthy people. Studies that may support broader use are preliminary and recommend additional research, though they may be useful to help individuals who exercise at extremely high levels dial in carbohydrate intake for exercise and recovery.

For people who choose to adopt CGMs, working with a physician to interpret the results is important. It’s easy to misread the results of CGM data because more things affect blood glucose levels than just carbohydrate intake.

For example, stress hormones can cause increases in blood glucose and may not be tied to an athletic activity. Certain types of exercise can cause blood sugars to rise where other workouts may cause them to decline. And people may respond differently to foods. Researchers are finding that CGMs can help define the body’s reaction to those inputs, but it’s still early to determine if they’re ready or necessary to help most people.

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About the Author
Janet Tiberian Author
Janet Tiberian, MA, MPH, CHES

Janet Tiberian is MDVIP's health educator. She has more than 25 years experience in chronic disease prevention and therapeutic exercise.

View All Posts By Janet Tiberian, MA, MPH, CHES
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