A new study being presented at the Annual Meeting of the European Association for the Study of Diabetes (EASD) in Milan (28 September – 2 October) shows that, with the right preparation and continuous glucose monitoring, people with type 1 diabetes can complete a marathon just as fast as those without the condition.
What the Study Looked At
Running 42 kilometres is a tough challenge for anyone. For people with type 1 diabetes, it brings an extra layer of complexity: constantly juggling energy burn, carbohydrate intake, insulin doses, and blood sugar levels, all while trying to keep up a steady pace.
Although many people with type 1 diabetes stay very active, there’s surprisingly little data on how blood sugar actually behaves during long endurance events like a marathon, or how reliable glucose monitoring technology is in those conditions. A team of researchers from the Poznan University of Medical Sciences and Raszeja City Hospital in Poland wanted to find out.
They followed 20 amateur runners in the 2025 Poznań Marathon. Half had type 1 diabetes (for at least a year) and half were runners without diabetes. The two groups were well matched: average ages of 35 and 40, each group had eight men and two women, and the diabetes group had a median diabetes duration of 16.5 years with well-controlled blood sugar overall (HbA1c of 6.4%).
Before the race, the researchers helped the diabetes group fine-tune their insulin. Those on multiple daily injections cut their basal insulin by 25%, those on standard insulin pumps cut it by 50%, and those on hybrid closed-loop systems set a target glucose of 150 mg/dL. Everyone aimed to start the race with blood sugar in the range of 140-200 mg/dL.
At the start, 10 km, 19 km, 30 km and finish, blood sugar was measured both with a traditional finger-prick glucometer and two different continuous glucose monitors (CGMs).
The Results Were Encouraging
All ten runners with type 1 diabetes completed the marathon, with no significant difference in finishing times between the two groups (228 minutes for the diabetes group versus 248 for controls).
Runners with diabetes consumed around 53.5 g of carbohydrate per hour during the race to help keep blood sugar steady. Their glucose readings dipped a little as the race progressed, from about 183 mg/dL at the start down to 108 mg/dL at the finish, which the researchers considered a good pattern.
Only one runner experienced low blood sugar during the race, and even they completed the marathon. Importantly, that runner had started below the recommended 140 mg/dL range, hinting that beginning the race well within the target zone really matters.
A Word of Caution About Glucose Monitors
One of the more surprising findings was how far the continuous glucose monitors drifted from the finger-prick measurements during the race. On average, CGM readings differed from the glucometer by around 37-43%, and they tended to overestimate blood sugar by a significant margin. In practice, that could lead a runner to believe their blood sugar is higher than it really is, which could delay essential carb top-ups.
The authors said: “In this small observational study, all runners with type 1 diabetes completed the marathon, with performance comparable to controls. The runner who experienced low blood sugar had started the race with a glucose level below 140 mg/dL. During the marathon, CGM readings differed from glucometer measurements. For longer endurance events, runners should therefore consider checking their glucose with a glucometer, especially when the sensor reading does not match how they feel.”
Overcoming the Fear of Exercise
For many people with type 1 diabetes, worries about low blood sugar can become a barrier to being active, even though exercise brings huge health benefits.
The authors said: “Fear of hypoglycaemia is the main barrier to physical activity and affects up to 45% of people with T1D despite the major health benefits of regular exercise. Managing glucose is challenging when glucose levels change rapidly and responses vary between individuals. Our study provides another example that, with appropriate education and careful blood sugar management, people with T1D can successfully take part in even very demanding endurance exercise.”
They were quick to add that marathon running shouldn’t be undertaken lightly: “People with T1D preparing for a marathon should discuss an individual glucose, carbohydrate, and hydration plan with their doctors before the event. The most important aspect is an appropriate insulin management strategy, including reductions in basal and/or prandial insulin. Of course, much depends on baseline blood sugar control, exercise experience, diabetes duration, the presence of diabetes-related complications, and many other individual factors. For example, some people should consult a cardiologist before starting endurance training. Our team supports many athletes with type 1 diabetes who have achieved remarkable goals, including competing at the Olympic Games, completing an Ironman triathlon or running 10 marathons in 10 consecutive days.”
The message is clear: with the right planning, support and awareness of each tool’s limits, a marathon medal is well within reach for people with type 1 diabetes.