Bolus insulin dose depends on previous‐day race intensity during 5 days of professional road‐cycle racing in athletes with type 1 diabetes: A prospective observational study

AIMS: To assess insulin therapy, macronutrient intake and glycaemia in professional cyclists with type 1 diabetes (T1D) over a 5‐day Union Cycliste Internationale road‐cycle race. MATERIAL AND METHODS: In this prospective observational study, seven professional cyclists with T1D (age 28 ± 4 years, body mass index 20.9 ± 0.9 kg/m(2), glycated haemoglobin concentration 56 ± 7 mmol/mol [7.3% ± 0.6%]) were monitored during a five‐stage professional road cycling race. Real‐time continuous glucose monitoring (rtCGM) data, smart insulin pen dose data and macronutrient intake were assessed by means of repeated‐measure one‐way ANOVA and post hoc testing. Associations between exercise physiological markers and rtCGM data, insulin doses and macronutrient intake were assessed via linear regression modelling (P ≤ 0.05). RESULTS: Bolus insulin dose was significantly reduced over the 5‐day period (P = 0.03), while carbohydrate intake (P = 0.24) and basal insulin doses remained unchanged (P = 0.64). A higher mean previous‐day race intensity was associated with a lower mean sensor glucose level (P = 0.03), less time above range level 2 (>13.9 mmol/L [250 mg/dL]; P = 0.05) and lower doses of bolus insulin (P = 0.04) on the subsequent day. No significant associations were found for any other glycaemic range and glycaemic variability (P > 0.05). CONCLUSIONS: This is the first study to demonstrate the influence of previous‐day race intensity on subsequent bolus insulin dose requirements in professional cyclists with T1D. These data may help inform therapeutic strategies to ensure safe exercise performance.