The Effects of Coffee on Glucose Metabolism by Tracey M. Robertson Submitted for the Degree of Doctor of Philosophy Faculty of Health and Medical Sciences University of Surrey April 2016 ©Tracey M. Robertson 2016 1 This thesis and the work to which it refers are the results of my own efforts. Any ideas, data, images or text resulting from the work of others (whether published or unpublished) are fully identified as such within the work and attributed to their originator in the text, bibliography or in footnotes. This thesis has not been submitted in whole or in part for any other academic degree or professional qualification. I agree that the University has the right to submit my work to the plagiarism detection service TurnitinUK for originality checks. Whether or not drafts have been so-assessed, the University reserves the right to require an electronic version of the final document (as submitted) for assessment as above. 2 It has been suggested that coffee drinking may confer a beneficial effect on health by reducing the risk of developing Type 2 Diabetes Mellitus (T2DM) and indeed there is much epidemiological evidence for a reduced incidence of T2DM in habitual coffee drinkers. However, many acute studies have reported a temporary worsening in postprandial glycaemia following caffeinated coffee (CC) consumption. Varied methodologies have been employed by these studies with many giving their participants large doses of coffee. In the acute studies conducted for this thesis, a single serving of CC increased the postprandial glycaemic response more than control (p=0.008), with no apparent dose- response effect. Furthermore, a single serving of decaffeinated coffee (DC) consumed in the morning, produced no effect on postprandial glycaemia, although a trend was observed for a reduction in the postprandial glucose peak (p=0.060) when DC was consumed at lunchtime. The majority of longer-term investigations have recruited habitual coffee drinkers who are likely to have already obtained any potential benefits of coffee consumption. The longer-term intervention reported in this thesis found no overall effects of twelve weeks of CC drinking on glucose and lipid metabolism in coffee-naïve individuals. However, differences were observed between fast and slow caffeine metabolisers when the analysis was split by phenotype. The fast caffeine metabolisers displayed a lower postprandial glucose response (p=0.019) and greater NEFA suppression (p=0.001) at baseline. Furthermore, significant interaction effects were observed between visit and phenotype for postprandial glucose (p=0.048) and NEFA (p=0.019), with the intervention producing an apparent increase in postprandial glycaemia in fast metabolisers and reduced NEFA suppression in slow metabolisers. In conclusion, no evidence was found for a beneficial effect of coffee drinking on glucose and lipid metabolism in the general population, however, individual differences in response to longer-term coffee drinking were observed which warrant further investigation. 3 First and foremost, I would like to thank my supervisors Denise Robertson and Mike Clifford, for their invaluable support and guidance throughout this PhD. They have always been there when I needed them, for which I am extremely grateful. My thanks also go to the BBSRC and my industrial sponsors, Campden BRI and Mondelez International, who funded this PhD and provided the coffee for my final study. In particular I would like to thank Gemma Chope, Simon Penson and Rachel Jeffries for their support throughout my studies. Thanks to all who helped with lab techniques and for the patience they displayed with a novice such as myself, including, but not limited to, Shelagh, Nicola, Caroline, Fariba, Fran, Jo and Benita. Particular thanks go to Mick Frank for the salivary caffeine analysis and to Professor Alan Crozier and Dr Iziar Amaia Ludwig Sanz Orrio at the University of Glasgow for the coffee analysis. Also Simon Archer and Daan van der Veen for guidance with my DNA assays. Peter Williams and Sig Johnsen also deserve thanks for putting up with my many statistics queries. Thanks also go to the undergraduate students who assisted me on two of my studies as part of their final year projects: Olivia Chesterman and Eithne McGonigle (repeated-dose study) and Ivey Zhang and Joanna Wyatt (twelve week intervention) and to the staff at the Surrey Clinical Research Centre who cannulated and collected blood from my participants for my final study. My study participants deserve special thanks for volunteering to take part in my studies. I should also perhaps apologise to several non-coffee drinkers who developed a serious coffee habit following my final study! Thanks also to my fellow PhD students and postdocs, past and present, for making my PhD such an enjoyable experience. In particular Caroline and Camilla, for showing me the ropes, and Andrea, Ghalia, Rona, Charlie, Sharaf, Simon and the two Najlaas for sharing the road (and office) with me. Finally, I would like to thank my family and friends for their support throughout. In particular Jon, for keeping me sane, feeding me, loving me and putting up with me during the dreaded writing phase and also to Nicola for sharing a laugh and a moan and providing cake for our morning coffee. 4 DECLARATION OF ORIGINALITY 2 SUMMARY 3 ACKNOWLEDGEMENTS 4 TABLE OF CONTENTS 5 FIGURES 11 TABLES 14 ABBREVIATIONS 16 CHAPTER 1. INTRODUCTION 19 1.1 Overview 19 1.2 Glucose homeostasis 19 1.2.1 Postprandial glucose metabolism 20 1.2.2 Glucose production: gluconeogenesis and glycogenolysis 21 1.2.3 Lipid metabolism 22 1.2.4 Regulation of glucose and lipid metabolism 23 1.2.5 Alterations to glucose homeostasis in T2DM 25 1.3 Coffee 27 1.3.1 Coffee consumption in the UK 27 1.3.2 Coffee production 27 1.3.3 Composition of green coffee beans 28 1.3.4 Composition of roasted coffee beans 29 1.3.5 Effects of the decaffeination process on coffee composition 30 1.3.6 Instant coffee composition 30 1.3.7 Composition of brewed coffees 31 1.3.8 Bioavailability of coffee components 32 1.4 Coffee and glucose metabolism 33 1.4.1 Epidemiology 33 1.4.2 Acute effects of coffee on glucose metabolism 35 1.4.3 Longer-term effects 36 5 1.4.4 Potential mechanisms 39 1.4.5 Effect of genotype 43 1.5 Aims of current work 45 1.6 Hypotheses 45 CHAPTER 2. GENERAL METHODS 46 2.1 Recruitment 46 2.2 Screening 46 2.2.1 Anthropometry 46 2.2.2 Screening blood samples 47 2.2.3 Normal caffeine intake 47 2.3 Blood sampling during postprandial tests 48 2.3.1 Capillary blood 48 2.3.2 Venous blood 48 2.4 Plasma and serum analysis 49 2.4.1 Analysis of plasma glucose 49 2.4.2 Analysis of serum total cholesterol 50 2.4.3 Analysis of serum HDL-cholesterol 51 2.4.4 Analysis of serum TAG 52 2.4.5 Analysis of serum NEFA 52 2.4.6 Analysis of plasma insulin 53 2.4.7 Analysis of serum IL-6 and TNF- 54 2.5 Salivary caffeine analysis 55 2.5.1 Saliva collection 55 2.5.2 Caffeine analysis 55 2.6 DNA analysis 55 2.6.1 DNA collection 56 2.6.2 DNA extraction 56 2.6.3 DNA analysis 56 2.7 Estimation of insulin sensitivity and beta cell function 58 2.8 Statistical analysis 58 6 CHAPTER 3. SYSTEMATIC REVIEW ON THE ACUTE EFFECTS OF COFFEE ON POSTPRANDIAL GLUCOSE RESPONSE 59 3.1 Introduction 59 3.2 Aims 59 3.3 Methods 59 3.4 Results 61 3.4.1 Participant characteristics 67 3.4.2 Methodology 67 3.4.3 Coffee dose 67 3.4.4 Caffeinated coffee 68 3.4.5 Decaffeinated coffee 69 3.5 Discussion 70 3.5.1 Effects of caffeinated coffee 70 3.5.2 Effects of decaffeinated coffee 71 3.5.3 Methodology 71 3.6 Conclusion 75 CHAPTER 4. DOSE-RESPONSE STUDY ON THE ACUTE EFFECTS OF COFFEE ON GLUCOSE RESPONSE 76 4.1 Introduction 76 4.2 Aims 76 4.3 Methods 77 4.3.1 Participants 77 4.3.2 Study design 77 4.3.3 General protocol 78 4.3.4 Drink composition 79 4.3.5 Blood collection 80 4.3.6 Statistical analysis 80 4.4 Results 81 4.4.1 Baseline characteristics 81 4.4.2 Glucose and insulin 81 4.4.3 Test drink organoleptic properties 86 7 4.5 Discussion 87 4.5.1 Escalating doses of decaffeinated coffee and caffeine 87 4.5.2 Escalating doses of decaffeinated coffee, all with 100 mg caffeine 89 4.5.3 Comparison of control drinks with and without added caffeine 90 4.5.4 Test drink organoleptic properties 90 4.5.5 Limitations/confounders 92 4.6 Conclusion 93 CHAPTER 5. THE ACUTE EFFECTS OF REPEATED DOSES OF DECAFFEINATED COFFEE ON THE POSTPRANDIAL GLUCOSE RESPONSE 95 5.1 Introduction 95 5.2 Aims 96 5.3 Methods 96 5.3.1 Participants 96 5.3.2 Study design 97 5.3.3 General protocol 97 5.3.4 Blood Collection 99 5.3.5 Statistical analysis 99 5.4 Results 100 5.4.1 Baseline characteristics 100 5.4.2 Glucose and insulin 101 5.5 Discussion 109 5.5.1 Circadian rhythms in postprandial glucose response 109 5.5.2 Effect of decaffeinated coffee at morning meal 109 5.5.3 Effect of decaffeinated coffee at lunchtime 111 5.5.4 Effects of morning decaffeinated coffee on the postprandial response to a subsequent meal 112 5.5.5 Effect of multiple doses of decaffeinated coffee 114 5.6 Study limitations 114 5.7 Conclusion 115 CHAPTER 6.