A Comparison of Circadian Rhythms in Day and Night Shift Workers
Total Page：16
File Type：pdf, Size：1020Kb
Portland State University PDXScholar Dissertations and Theses Dissertations and Theses 1990 A comparison of circadian rhythms in day and night shift workers Mary Lee Blood Portland State University Follow this and additional works at: https://pdxscholar.library.pdx.edu/open_access_etds Part of the Physiology Commons, and the Psychology Commons Let us know how access to this document benefits ou.y Recommended Citation Blood, Mary Lee, "A comparison of circadian rhythms in day and night shift workers" (1990). Dissertations and Theses. Paper 3991. https://doi.org/10.15760/etd.5875 This Thesis is brought to you for free and open access. It has been accepted for inclusion in Dissertations and Theses by an authorized administrator of PDXScholar. Please contact us if we can make this document more accessible: [email protected]. AN ABSTRACT OF THE THESIS OF Mary Lee Blood for the Master of Science in Psychology presented October 29, 1990. Title: A Comparison of Circadian Rhythms in Day and Night Shift Workers. APPROVED BY THE MEMBERS OF THE THESIS COMMITTEE: Cord B. Sengstake, Chair Alfred J. Lewy Robert L. Sack Gary Brodowicz The present study examined whether and to what extent physiological rhythms of long-term . night workers become adapted to their unconventionally scheduled hours of work and sleep and how 2 the degree of adaptation would be reflected in ratings of sleep quality, mood, anxiety, energy and satisfaction. Many physiological functions such as the release of hormones, excretion of metabolites and fluctuation of core temperature follow predictable circadian (24-hour) rhythms that are regulated by a pacemaker thought to be located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The timing of the production of the hormone melatonin was chosen as an indicator of physiological adaptation because its rhythm closely reflects the phase of the SCN. Ordinarily, melatonin is produced only at night and its onset, generally occurring one to several hours prior to sleep, can be determined with a high degree -0f accuracy. The melatonin rhythm is masked (obscured) only by bright light as opposed to other common measures which may be masked by sleep, activity, diet and stress. Therefore if bright light is avoided during the time of measurement, the melatonin rhythm provides an accurate reflection of its circadian pacemaker. Nine night workers were studied at a local hospital following their last shift of the week. They entered dim light and 5 ml blood samples were drawn hourly for the next 24-hours to determine the timing of their dim light melatonin onset (DLMO). A comparison group of nine day workers was also studied, however, samples were taken for only six hours surrounding the time of the expected DLMO (i.e, 1800 - 2300). Subjects kept daily diaries for the two weeks 3 prior to admission, recording sleep times, sleep quality, sleepiness, mood, anxiety, energy and light exposure. Subjects also completed several scales in order to assess mood state, neuroticism, extraversion and diurnal (morning vs. evening) orientation for best functioning. The timing of night workers' DLMOs (median = 14.47 h) was remarkably different from that of day workers (median = 21.30 h) (p < .001, Mann-Whitney U test), suggesting that for most night workers, a great deal of physiological adaptation had taken place. An unexpected finding was that the night workers' DLMOs occurred at a delayed phase in relation to sleep. Despite this, night workers obtained similar amounts of sleep and rated sleep quality comparably to day workers. Although night workers tended to sleep at more conventional times and obtain more total sleep on their non work days, they rated sleep quality, mood, anxiety and energy comparably to work days. There was a great deal of variability in night workers' scores on psychological measures. However, for the most part, scores fell within the average range compared to normative samples. With the possible exception of neuroticism scores, which followed the expected pattern for all but two of the night workers, none of the other measures seemed promising as predictors of degree of adaptation. These results suggest that this group of night workers is moderately well adapted to a schedule of nighttime work and 4 daytime sleep. In most cases, lack of physiological adaptation is seen in an "overly delayed" circadian phase. Several clinical treatments are suggested as ways in which better adaptation might be obtained. Scheduling sleep so it occurs at a later time, more in phase with the circadian pacemaker is a simple suggestion, but perhaps the least agreeable to the night worker. Treatments of appropriately timed bright light and/or exogenous melatonin administration are discussed as possible techniques that may be utilized to advance the circadian pacemaker so that it is better synchronized with work and preferred sleep times. A COMPARISON OF CIRCADIAN RHYTHMS IN DAY AND NIGIIT SHIFf WORKERS by MARYLEE BLOOD A thesis submitted in partial fulfillment of the requirements for the degree of MASIBR OF SCIENCE 1n PSYQIOLOGY Portland State University 1990 TO THE OFFICE OF GRADUATE S11JDIES: The members of the Committee approve the thesis of Mary Lee Blood presented October 29, 1990. ~ _.r-__ Cord B. Sengstak:e, Chair ~~ ...... ~~""" ... ~ Nancy A. Perri ~~...... ~ ·~~~~ .~~~~~ ·~~~~ · Alfred J. Lewy _j_{,.,f,,,!,±_/( dt.vL-·---- Robert L. Sack _1~ Jll ~.--=c_l__,,_,,. Gafy Brodowicz APPROVED: ~ Cord B. Sengstak:e, Chair, Department of Psychology e. tJtiL C. William Savery, Interim ovost for Graduate Studies and Research ACKNOWLEDGEMENTS I would like to thank the staff of the Sleep and Mood Disorders Laboratory at Oregon Health Sciences University. Special Thanks to Greg Clarke, Mary Cardoza, Vance Bauer, Jaqueline Authier, David Wesche and Carol Simonton. I would also like to thank Dr. Robert Sack, Dr. Alfred Lewy and Dr. Jeanne Latham for their medical assistance. I wish also to thank the nursing and dietary staff of the Clinical Research Center. TABLE OF CONTENTS PAGE ACKN"OWLEDGEMENTS ......................................................................... iii LIST OF FIGURES ....................................................................................... vii CHAPTER I INTRODUCTION ................................................................. 1 II RESEARCH ON THE CIRCADIAN RHYTHMS OF NIGHT WORKERS ................................ 6 Field Studies .. .. .. .. .... .. .... .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. .. .. .. .. 6 Laboratory Studies .. ..... ..... .... ................................... 7 Masking and the Use of Constant Routines .... 8 Melatonin ..................................................................... 12 Personality .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..... .. .. .. .. .. 14 III RATIONALE AND OUTLINE OF THE STUDY ............ 16 Physiological Adaptation ..... ..... ...... ...... ....... ..... ..... 16 Psychological Adaptation . ...... ..... ...... .. ....... ...... ... 18 N METHODOLOGY AND PROCEDURES ............................. 19 Subjects . .... ... .... ... .... .... ... ... ... .... ... .... .... .. ..... .. ... .. ........ 19 Night Workers Day Workers v CHAPfER PAGE Procedures . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. 19 Night Workers Day Workers Procedures Common to Both Groups Analysis of Physiological Samples V RESULTS OF THE STUDY ..................................................... 27 Physiological and Behavioral Measures.............. 27 Dim Light Melatonin Onsets Sleep Psychological Measures.............................................. 34 Profile of Mood States Eysenck Personality Inventory Morningness Eveningness Questionnaire General Health and Adjustment Questionnaire Life Satisfaction Self-reported Daily Ratings VI CONCLUSIONS AND RECOMENDATIONS ........................ 41 REFERENCES ................................................................................................. 52 Vl APPENDICES A DAILY DIARY AND INSTRUCTIONS .......................................... 60 B GRAPHIC REPRESENTATION OF INDIVIDUAL NIGHT WORKER SLEEP PATIERNS ........................................................... 65 C PHYSICAL SYMPTOMS ................................................................... 75 D LIFESTYLE .......................................................................................... 78 E CASE REPORTS FOR INDIVIDUAL NIGHT WORKERS ............. 81 LIST OF FIGURES FIGURE PAGE 1. The relationship of the dim light melatonin onset and average sleep periods in day and night shift workers . .. .. .. .. .. ... .. .. .. .. .. .. .. .. .. ..... .. .. .. .. .. .. .. .. .. .. .. .. .. 28 2. Night workers' melatonin onsets with proximal sleep and work periods. ................ ............. .. ............ .. ..... .......... ............ .......... 29 3. Percentage of day and night shift workers asleep during an average 24-hour period .... ~.............. .................. ................. 32 4. Sleep strategies in two "moderately morning" type night workers ............ ................ .......... ... ....................... ..... ...... .. .... 41 , CHAPTER I INTRODUCTION Shift work, which involves working irregular or nontraditional hours, is a part of working life for millions of Americans. Estimates on the percentage of the population who are exposed to work patterns that involve disruption of the normal daytime work/nighttime sleep orientation vary. According to the Bureau of Labor statistics, approximately