Challenging the human circadian clock by Daylight Saving Time and Shift-Work Academic Dissertation (Doctor rerum naturalium) At the Centre for Chronobiology Institute for Medical Psychology Ludwig-Maximilians-University Munich Written by Thomas Kantermann Born 26th of February, 1979 in Gütersloh Arbeit eingereicht am: 17.07.2008 1. Gutachter / Prüfer: Prof. Gisela Grupe 2. Gutachter / Prüfer: Prof. Benedikt Grothe 3. Prüfer: Prof. Susanne Foitzik 4. Prüfer: Prof. Gerhard Haszprunar Sondergutachter: Prof. Till Roenneberg Tag der mündlichen Prüfung: 15.12.2008 Für meine Schwester Stefanie „Probleme kann man niemals mit derselben Denkweise lösen, durch die sie entstanden sind.“ Albert Einstein dt.-amerikan. Physiker, 1921 Nobelpreis für Physik 1879 – 1955 Contents 1. INTRODUCTION ..................................................................................... 1 1.1. Biological (circa-) Rhythms..........................................................................................2 1.2. Sleep.............................................................................................................................4 1.2.1. Two Process Model of Sleep..................................................................................6 1.2.2. Circadian Rhythm Sleep Disorders, Sleepiness and Fatigue....................................7 1.3. The Internal Clock ........................................................................................................8 1.3.1. Phase of Entrainment – Chronotype .....................................................................11 1.3.2. Challenges to the circadian clock from real life....................................................14 1.3.2.1. Internal Desynchronisation............................................................................15 1.3.2.2. Social Jetlag ..................................................................................................16 2. AIMS OF THIS WORK .......................................................................... 18 2.1. Daylight Saving Time (DST) and the Human Clock (Chapter 3).................................18 2.2. Shift-Work and the Human Clock (Chapter 4).............................................................19 2.2.1. Potential Health Costs from Shift-Work (Chapter 4.7.3).......................................19 2.3. Shift-Work/Social-Jetlag-Model (Chapter 5)...............................................................20 3. DAYLIGHT SAVING TIME (DST) AND THE HUMAN CLOCK – A FIELD SURVEY ........................................................................................ 21 3.1. Introduction ................................................................................................................21 3.1.1. Brief History of Daylight Saving Time.................................................................21 3.1.2. Brief History of Studies on Daylight Saving Time................................................22 3.2. The Study on Daylight Saving Time ...........................................................................23 3.3. Methods......................................................................................................................24 3.4. Results........................................................................................................................28 3.5. Discussion ..................................................................................................................32 4. SHIFT-WORK AND THE HUMAN CLOCK – A LITERATURE SURVEY .......................................................................... 35 4.1. Introduction ................................................................................................................35 4.1.1. Definition of Shift-Work......................................................................................37 4.1.2. Reasons for doing Shift-Work..............................................................................38 4.1.3. Shift-Work and Social Strata................................................................................39 4.1.4. Epidemiological terms..........................................................................................40 4.2. Rationale for the Study on Shift-Work ........................................................................42 4.3. Methods......................................................................................................................43 4.4. Results........................................................................................................................44 4.4.1. Why no Meta-Analysis?.......................................................................................47 4.4.2. Key epidemiological Studies................................................................................48 4.4.3. Occupations .........................................................................................................48 4.4.4. Sexes / Genders....................................................................................................49 I 4.4.5. Questionnaires and Interviews..............................................................................49 4.4.5.1. Pros and Cons of Questionnaires ...................................................................51 4.5. Findings from the selected Articles .........................................................................52 4.5.1. Shift-Work and Sleep.......................................................................................53 4.5.2. Shift-Work Tolerance - Shift-Work Sleep Disorder (SWSD)............................58 4.5.3. Shift-Work and the Cardiovascular System ......................................................59 4.5.4. Cardiovascular Risk and Lifestyle Factors........................................................64 4.5.5. Shift-Work and Cancer.....................................................................................70 4.5.7. Shift-Work and Metabolism .............................................................................77 4.6. Methodological Difficulties with the Shift-Work Literature ....................................80 4.7. Discussion ..................................................................................................................82 4.7.1. The Direction of Shift-Work Rotation ..................................................................92 4.7.1.1. Review of the Literature................................................................................92 4.7.1.2. Evidence from the articles on the effect of the direction in shift rotation........95 4.7.2. Direction of Shift-Work Rotation and Stress ........................................................99 4.7.3. Potential Health Costs from Shift-Work .............................................................101 5. SHIFT-WORK/SOCIAL-JETLAG-MODEL ...................................... 104 5.1. Introduction ..............................................................................................................104 5.2. Rationale for the Shift-Work/Social-Jetlag-Model.....................................................104 5.3. Methods....................................................................................................................105 5.4. Results......................................................................................................................111 5.5. Discussion ................................................................................................................113 6. CONCLUSION ...................................................................................... 115 6.1. Daylight Saving Time (DST) and the Human Clock (see Chapter 3) .........................115 6.2. Shift-Work and the Human Clock (see Chapter 4).....................................................115 6.2.1. Potential Health Costs from Shift-Work (see Chapter 4.7.3)...................................116 6.3. Shift-Work/Social-Jetlag-Model (see Chapter 5).......................................................116 6.4. Outlook on the applicability of the Shift-Work/Social-Jetlag-Model .........................116 7. SUMMARY............................................................................................ 118 7.1. Appeal: Importance of Chronotype in Medical Research...........................................119 8. REFERENCE LIST............................................................................... 121 9. FIGURE LIST........................................................................................ 134 10. TABLE LIST........................................................................................ 138 11. ERKLÄRUNG ..................................................................................... 140 12. CURRICULUM VITAE...................................................................... 141 13. ACKNOWLEDGEMENTS................................................................. 143 II 1. Introduction Good timing is a crucial attribute in nature. Being at the right time at the right place increases fitness and the chance to survive. Crucial and general as this statement may be, its principals can be found manifold in nature. These principles are reflected in complex interactions from human individuals as also from molecules in a cell. Bees and butterflies, for example, increase their fitness and chance to survive when they are aware of the time of their favoured flowers opening their blossoms to provide access to their nectar.