Abstract
Introduction: Type 2 diabetes is a common non-infectious disease affecting about 90% of the global diabetes population (463 million), and glucose control is the primary goal of diabetes management to reduce diabetes-related complications and premature mortality and improve quality of life. Previous studies have reported associations of sedentary time with high fasting glucose and postprandial glucose and beneficial effects of breaks in sedentary time on postprandial glucose and daily glucose levels. However, there is limited evidence on the associations of sedentary time and breaks in sedentary time with intra-day glucose control in free-living settings. Moreover, dose-response relationships between frequency of breaks in sedentary time and glucose control need to be investigated. This thesis aimed to investigate: (1) whether glucose profiles are well controlled throughout the day, (2) the associations of sedentary time and breaks in sedentary time with intra-day glucose control in free-living settings, and (3) dose response relationships between frequency of breaks in sedentary time and glucose control in a laboratory setting in Type 2 diabetes.Methods: To fulfil the thesis aims, three studies were conducted: a systematic review and meta-analysis (Study 1), a cross-sectional study (Study 2) and a randomised crossover trial (Study 3). In Study 1, observational studies reporting intra-day glucose profiles using continuous glucose monitoring (CGM) in people with Type 2 diabetes were identified, and mean differences between reported glucose profiles and the International Diabetes Federation (IDF) targets at different times of the day were analysed. Study 2 was conducted in thirty-seven participants with Type 2 diabetes (age, 62.8 ± 10.5 years; body mass index, 29.6 ± 6.8 kg/m2 ), and the associations of sedentary time and breaks in sedentary time with intra-day glucose control were investigated using regression analysis and general linear model univariate analysis. In Study 3, twelve adults with Type 2 diabetes (age, 60.0 ± 3.2 years; body mass index, 30.2 ± 1.4 kg/m2 ) completed two of three conditions: sitting for 7 hours interrupted every (1) 60 min (Condition 1), (2) 30 min (Condition 2), and (3) 15 min (Condition 3) by 3 min of light-intensity walking breaks, and dose-response was investigated using multilevel mixed-effects linear regression. The activPAL3 activity monitor and the FreeStyle Libre flash glucose II monitoring system (Abbott Diabetes Care, Alameda, CA) were respectively used to assess physical activity/sedentary behaviour and glucose in both Study 2 and Study 3.
Results: Study 1 found that pooled fasting glucose (pre-breakfast glucose), postprandial glucose after breakfast and post-breakfast glucose spike were significantly higher than the IDF targets. Independent of HbA1c (glycated haemoglobin), fasting glucose and postprandial glucose after breakfast were not well-controlled in those with Type 2 diabetes. Pre-lunch glucose, pre-dinner glucose and postprandial glucose after lunch and dinner were also above the IDF targets but not significantly. Study 2 observed the detrimental associations of sedentary time with time in euglycaemia, time in target glucose range (TIR), pre-breakfast glucose, pre-dinner glucose, post-lunch glucose, post-dinner glucose and the dawn phenomenon and the beneficial associations of breaks in sedentary time with euglycaemia, TIR, pre-breakfast glucose, pre-dinner glucose, post-breakfast glucose and the dawn phenomenon. In Study 3, dose-response between frequency of breaks in sedentary time and glucose control was observed. Fasting glucose, duration of the dawn phenomenon, night-time glycaemic variability, post-breakfast glucose, post-lunch glucose, post-dinner glucose, cumulative 10.5-h postprandial glucose and 21-h glucose were significantly lower for Condition 3 compared with Condition 1. Condition 3 significantly reduced the magnitude of the dawn phenomenon, night-time glycaemic variability and 21-h glucose relative to Condition 2. Compared with Condition 1, significant attenuations of post-lunch glucose and post-dinner glucose were observed in Condition 2.
Conclusions: The overall conclusions from the work completed are as follows: (1) In people with Type 2 diabetes, glucose profiles throughout the day, particularly fasting glucose and postprandial glucose after breakfast, are not well-controlled independent of HbA1c. (2) More time spent in unbroken and continuous sedentary behaviour predicts poor intra-day glucose regulation. Conversely, breaks in sedentary time could be clinically relevant to improve intra-day glucose regulation. (3) Interrupting sedentary time every 15 min could produce better glucose control than interrupting sedentary time III every 30 min and 60 min, and these findings could be used to develop effective interventions for better glycaemic control in Type 2 diabetes.
| Date of Award | 2021 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Sebastien Chastin (Supervisor) & Andrew Collier (Supervisor) |