Type 1 Diabetes with Metabolic Syndrome Features: Exploring this Modern-Day Phenotype and the Effects of High-Intensity Interval Training

Abstract

Introduction Type 1 diabetes is characterised by insulin deficiency, however the ‘double diabetes’ phenotype of type 1 diabetes with insulin resistance and/or metabolic syndrome is becoming increasingly recognised, especially given rising global obesity rates. The effects of exercise on metabolic health have not been adequately studied in people with type 1 diabetes, and exercise-related hypoglycaemia is a major barrier.

Aims This thesis aimed to examine the prevalence of metabolic syndrome in adults with type 1 diabetes, and its association with diabetes complications. The safety and benefits of high-intensity interval training (HIIT) on glycaemic control, cardiometabolic measures and liver fat were studied in people with type 1 diabetes and metabolic syndrome features.

Methods Three related studies were conducted. Firstly, a cross-sectional study examined the prevalence of metabolic syndrome in type 1 diabetes, and its age-related association with diabetes complications. Secondly, the safety of HIIT in type 1 diabetes on exercise-related hypoglycaemia was examined in a pilot study using continuous glucose monitoring. Thirdly, a randomised controlled trial examined the effect of HIIT on HbA1c, cardiometabolic health and liver fat in adults with type 1 diabetes and overweight or obesity.

Results Metabolic syndrome was common in adults with type 1 diabetes and was associated with a higher prevalence of diabetes complications, with the greatest impact at a younger age. HIIT performed with diabetes self-management strategies was not associated with increased exercise-related hypoglycaemia over 24 hours. In the randomised controlled trial, 12 weeks of HIIT did not significantly reduce HbA1c compared with control (-0.53% vs -0.14%, p=0.08). After 24 weeks, HIIT resulted in improvements in HbA1c, cardiorespiratory fitness and body composition compared with baseline. There was a favourable trend towards liver fat reduction with HIIT.

Conclusions Metabolic syndrome can identify a high-risk population of type 1 diabetes, who may benefit from interventions targeting insulin resistance and cardiometabolic risk. This thesis provides novel evidence that HIIT can be performed safely, and can improve glycaemic control and cardiometabolic health in people with type 1 diabetes and metabolic syndrome features.