How Ascorbic Acid and Exercise Affect Glucose Monitor Accuracy in Type 1 Diabetes

Continuous glucose monitors (CGMs) are sensors that track your blood sugar throughout the day. Different CGM systems use different technologies to measure glucose. This study focused on a newer CGM design that uses GDH-FAD technology—a type of enzyme sensor—and wanted to know how accurately it works in real conditions.

The researchers compared the new CGM's readings to a reference laboratory device (the YSI 2300), which is the gold standard used by the FDA to evaluate glucose monitors. This comparison tells us whether a CGM is giving you trustworthy numbers.

The study included adults with Type 1 diabetes aged 18 to 65 who had stable insulin treatment for at least three months. Participants visited the clinic three times for controlled testing. At each visit, researchers gave participants two meals designed to cause noticeable changes in blood sugar—the kind of glucose swings that happen in real life.

On the second and third visits, participants also did moderate exercise between their meals. Additionally, some participants received a 1000 mg dose of ascorbic acid (vitamin C) at one of those visits. The researchers wanted to see whether these two common factors—exercise and vitamin C—changed how accurate the CGM readings were compared to the lab reference measurements.

The researchers used several methods to check accuracy. The main approach looked at what percentage of CGM readings fell within a certain distance of the lab reference values. For higher blood sugars (above 100 mg/dL), they checked if CGM values were within 15 percent. For lower values (100 mg/dL or below), they looked for readings within 15 mg/dL. They also calculated how far off the CGM readings were on average (a measure called MAD) and the relative error (MARD).

They analyzed performance across different blood sugar ranges to see whether the CGM's accuracy was consistent whether your blood sugar was low, in range, or high.

This type of research helps CGM manufacturers refine their devices and understand how real-world factors affect sensor performance. Knowing whether things like vitamin C supplements or exercise influence your monitor's accuracy can help you interpret your readings more confidently.

The study was conducted in a controlled clinic setting with measured meals and supervised exercise. Results from such studies don't always translate directly to everyday life, where many other factors—sweat, body position, individual metabolism—might also play a role. Additional research in real-world conditions helps researchers understand the full picture.

Source: Diabetes therapy : research, treatment and education of diabetes and related disorders. Evidence type: PubMed indexed literature. Type1Cure is an information and intelligence hub, not a medical advice service. This article summarizes published research and does not provide diagnosis, treatment, or personal medical guidance. Always talk to your own care team before changing anything about your Type 1 diabetes management.