Type 2 Diabetes Mellitus in Transitional Thailand: Incidence, Risk Factors, Mediators, and Implications
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Type 2 diabetes mellitus in transitional Thailand: incidence, risk factors, mediators, and implications Keren Papier December 2017 A thesis submitted for the degree of Doctor of Philosophy of The Australian National University © Copyright by Keren Papier 2017 All Rights Reserved Declaration I declare that the work contained in this thesis is the result of my original research and has not been submitted to any other University or Institution. This thesis was undertaken between March 2014 and December 2017 as a PhD Candidate enrolled at the Australian National University. Keren Papier December 2017 i Acknowledgments Numerous individuals deserve recognition for their guidance, support, and encouragement, without which this research would not have been completed. First, I would like to thank my principal supervisor Adrian Sleigh, who continually supported the development of my research and professional skills and was there for me when I needed guidance but also allowed me to have space to work independently. The other members of my supervisory panel were similarly supportive. Susan Jordan, with her door always open, has spent countless hours assisting me with all aspects of this research, provided ongoing support, encouragement and technical expertise, and encouraged me to be an active thinker. Cate D’este showed patience without measure, motivated me to embark on new analytical adventures, and always supported with interpretation. Chris Bain, with his remarkable ability to think outside the box, has challenged me to understand what I am doing and to think critically. Sam-ang Seubsman, who assisted with my field work in Thailand, supported all aspects of my research; without her this work would not have been possible. Cathy Banwell whose positive attitude, wisdom, and advice helped guide me forward. And Vasoontara Yiengprugsawan, who has been supportive and encouraging throughout the duration of this research. I gratefully acknowledge the Australian National University for providing financial funding to complete my research in the form of an Australian Government Research Training Program Scholarship. I also wish to express my sincere gratitude to Adele Green, Penny Webb, and David Whiteman at the QIMR Berghofer Medical Research Institute for welcoming me as a visiting student for nearly four years. To my wonderful colleagues in the Thai Health-Risk Transition Study, I feel truly lucky to have met you all and to have been a part of this extraordinary cohort. To the wonderful friends I made during my candidature, Suni, Liz, Jean-Claude, Lena, Annika, Mary, Ellie, Katie, Suzy, Libby, Jenny, Rimante, thank you for making this experience so memorable. Finally, thank you to my dear friends Kandice, Kelly, Chris, Janna, Gil, Liat, Natasha, my parents for your ongoing love and support, Lee for your thoughtful advice; and my husband Joshua, who is my greatest support and inspires me to be better every day. I am truly grateful to have you in my life. ii Abstract Background Economic growth in Asia is changing population health profiles. Family structures, environments, occupations, education, and health behaviours have also changed and science-based health services have evolved. As part of this ‘health-risk transition’, non- communicable diseases including type 2 diabetes mellitus (T2DM) have emerged. While the major causes of the diabetes epidemic in western, high-income countries are well documented, little is known of T2DM in developing Asia. The knowledge gap includes Thailand, which needs to identify local factors driving its T2DM epidemic. Aim This thesis aims to better understand the epidemiology of T2DM emerging in Southeast Asia. Methods Participants were from the Thai Cohort Study (TCS) of the health-risk transition. They were distance-learning adult students living all over Thailand, enrolled at Sukhothai Thammithirat Open University, and surveyed in 2005, 2009, and 2013 using mailed questionnaires that covered socio-demographic characteristics, lifestyle behaviours and self-reported health outcomes. In addition to these data, physician telephone interviews were conducted to validate self-reported questionnaire responses (2015); and a dietary survey was conducted to assess transitional dietary patterns (2015). Multiple logistic regression was used to calculate odds ratios and 95% confidence intervals (CIs) for longitudinal associations between exposures of interest and T2DM. Non-linear associations of body mass index (BMI) and T2DM were modelled using restricted cubic splines. Counterfactual mediation analysis explored sugary drink linkage to T2DM. Population attributable fractions and potential impact fractions were calculated. Principal component analysis identified dietary patterns and multivariable linear regression produced standardized coefficients and 95% CIs for associations between socio-demographic measures and dietary pattern scores. iii Results Physician telephone interviews of a cohort sample demonstrated high validity of questionnaire self-reported doctor diagnosed T2DM suggesting that self-reported doctor diagnosed T2DM is a feasible and acceptable method for assessing diabetes in epidemiological studies. Overall eight-year T2DM incidence was 177 per 10 000 (95% CI 164-190) with higher incidence in men. For both sexes, factors most strongly associated with T2DM risk were greater age and BMI. Two-thirds of all T2DM cases could be attributed to overweight and obesity. T2DM risk increased at BMI levels <23kg/m2. The increasing T2DM risk associated with body size became statistically significant at a BMI of 22 kg/m2 and 20 kg/m2 in men and women, respectively. For both sexes, living in urban areas increased T2DM and risk of consuming unhealthy dietary patterns, while a higher income associated with healthy dietary patterns. In Thai men, smoking and alcohol consumption increased T2DM risk. In women, sugary-drink consumption increased T2DM risk, of which 23% was mediated through obesity. In men, income and education were associated with increased T2DM risk. In women, education protected against unhealthy dietary intake. Overall, women tended to have safer behaviours (e.g. low prevalence of smoking and alcohol consumption) and better outcomes (e.g. lower prevalence of obesity and lower rates of T2DM). Conclusions Findings from young to middle-aged, educated Thai adults nationwide show that self- report of incident T2DM is a valid method for assessing diabetes in epidemiological studies, T2DM incidence in Thailand is high, and accompanying lifestyle and socio- demographic transitions are driving the T2DM epidemic. Thai men are likely to be in the middle stages of the health-risk transition while women are more advanced. Health-risks for T2DM are changing substantially and could be modified. These risks need to be targeted to prevent and control diabetes in Thailand. iv Table of Contents Declaration ......................................................................................................................... i Acknowledgments ............................................................................................................. ii Abstract ............................................................................................................................ iii Table of Contents .............................................................................................................. v List of Tables ................................................................................................................... viii List of Figures ................................................................................................................... ix Publications, presentations awards and activities ............................................................ x Contribution declaration for publications ..................................................................... xiii Collaborating authors ................................................................................................. xiii Acronyms and abbreviations ......................................................................................... xiv 1 Introduction ............................................................................................................... 1 1.1 Overview ............................................................................................................. 1 1.2 Study setting ....................................................................................................... 1 1.3 Type 2 diabetes mellitus ..................................................................................... 3 1.3.1 Definition ..................................................................................................... 3 1.3.2 Pathophysiology .......................................................................................... 3 1.3.3 Clinical Features .......................................................................................... 4 1.3.4 Summary – T2DM ........................................................................................ 5 1.4 Diagnosing diabetes ........................................................................................... 6 1.4.1 Diagnostic criteria ....................................................................................... 6 1.4.2 Diagnosis and validation in epidemiological studies ................................ 10 1.4.3 Summary – T2DM diagnosis ...................................................................... 13 1.5