Marathon Running With Type 1 Diabetes Can Be Safe, Small Study Suggests
Running 42 kilometres is a demanding test of endurance for any amateur athlete. For people living with type 1 diabetes, the challenge carries an extra layer of complexity that has little to do with fitness. Blood glucose can shift unpredictably across hours of sustained exercise, and the technology used to track it has rarely been evaluated under the messy, real-world conditions of an actual race.
New research scheduled for presentation at the Annual Meeting of the European Association for the Study of Diabetes (EASD) in Milan, Italy, from Sept. 28 to Oct. 2 indicates that with the help of continuous glucose monitoring (CGM) devices, people with type 1 diabetes can complete a marathon safely and record finishing times similar to those of runners without diabetes.
What the Researchers Set Out to Measure
The work was carried out by Michał Kulecki, Dr. Andrzej Gawrecki and colleagues at Poznan University of Medical Sciences and Raszeja City Hospital in Poznan, Poland. Their observational study followed participants through the 2025 Poznań Marathon, a standard 42-kilometre (26-mile) race, and focused on three things: how glucose levels behaved over the course of the event, how much carbohydrate runners consumed, and how accurately CGM sensors tracked blood sugar while the body was under prolonged endurance stress.
The team enrolled 20 amateur runners in total. Half were living with type 1 diabetes, each of whom had been diagnosed at least a year before the race. The other half served as controls without diabetes. According to the researchers, the two groups had comparable baseline characteristics.
Evidence on blood sugar patterns and CGM accuracy during extended endurance exercise in real race conditions has been limited, which is precisely the gap this study was designed to address.
Race-Day Strategy: Targets, Insulin Adjustments and Devices
Managing type 1 diabetes over a marathon means balancing several variables at once — energy expenditure, carbohydrate intake, insulin dosing and glucose monitoring. The Polish team approached that balance with a structured plan.
Pre-race glucose targets
For participants with type 1 diabetes, the target glucose range before the start was set at 140–200 mg/dL, giving runners a buffer of circulating glucose as they began to burn through it.
Basal insulin reductions
Insulin delivery was adjusted ahead of the race according to the type of technology each runner used:
- People using multiple daily injections (MDI) reduced their basal insulin doses by 25%.
- Those using non-hybrid insulin pumps reduced basal doses by 50%.
- Participants using hybrid closed-loop systems set a target glucose of 150 mg/dL.
Five of the ten runners with type 1 diabetes used multiple daily injections, three used continuous subcutaneous insulin infusion (CSII), and two used automated insulin delivery (AID) systems — a mix that reflects the real diversity of diabetes management among active adults.
Monitoring at Five Checkpoints
Data collection took place at five points along the course: the start, 10 km (6.2 miles), 19 km (12 miles), 30 km (19 miles) and the finish line. At each checkpoint, the research team measured glucose with a glucometer and compared those readings against two CGM systems — one that is intermittently scanned and one that operates in real time.
Throughout the race, the researchers administered carbohydrates or insulin as needed, depending on what the readings showed. This meant the study captured not just what happened physiologically, but how a monitoring-guided strategy played out under competitive conditions.
How the Team Judged Sensor Accuracy
To evaluate how well the CGM devices performed, the investigators used mean absolute relative difference (MARD), a standard metric for these systems. MARD expresses the average absolute percentage difference between a sensor's glucose reading and a reference glucose value. A lower MARD generally indicates closer agreement between the sensor and the reference measurement, making it a useful benchmark when conditions — sweat, motion, changing body temperature, rapid glucose flux — might otherwise compromise a sensor's reliability.
Why the Findings Matter
Type 1 diabetes has historically been framed as a reason for caution around extreme endurance events, and the physiology involved is genuinely demanding. Muscle contractions during a marathon can pull glucose out of the bloodstream, while the stress response triggered by prolonged exertion can push it the other way. Getting the balance wrong in either direction can end a race — or require medical attention.
What this small study suggests is that the combination of careful pre-race planning, insulin adjustment tailored to each runner's delivery method, and repeated CGM checks throughout the course may be enough to let athletes with type 1 diabetes line up alongside everyone else and finish on comparable terms. For the many people with the condition who want to take on long-distance events, that is a meaningful signal.
Caveats to Keep in Mind
The results should be read with appropriate caution for several reasons:
- The study was observational rather than a randomised controlled trial, so it cannot establish cause and effect.
- Only 20 runners took part, which limits how broadly the findings can be generalised.
- Participants were amateur athletes who had already chosen to attempt a marathon, so they may not represent all people with type 1 diabetes.
- The work is being presented at a scientific meeting and, as such, has not necessarily completed the full journal peer-review process.
Even so, the study offers a detailed picture of marathon-day glucose management using currently available technology — an area where real-world data has been scarce.
Practical Takeaways for Athletes With Type 1 Diabetes
While individual plans must always be developed with a diabetes care team, the study's design highlights several principles that endurance athletes and their clinicians may find useful:
- Start with a defined pre-race glucose target rather than an improvised one.
- Adjust basal insulin in advance, with the size of the reduction matched to the delivery system being used.
- Check glucose at regular intervals along the course, not only when something feels wrong.
- Carry both carbohydrate and insulin so that readings in either direction can be addressed during the race.
- Understand the accuracy limits of the sensor being worn, since performance can vary under exercise conditions.
What Comes Next
The research is due to be presented at the EASD Annual Meeting in Milan, where the team's full dataset — including glucose patterns across the five checkpoints and the MARD results for both CGM systems — will be shared with the diabetes research community. Those detailed figures will help clarify how closely sensor readings tracked reference glucose values over 42 kilometres, and where the technology may still need improvement for endurance sport.
For now, the headline is a cautiously encouraging one: with the right preparation and monitoring, a marathon finish line is not off limits for people with type 1 diabetes.
This article is based on reporting by Medical Xpress. Read the original article.
Originally published on medicalxpress.com
