Shift work and awakening cortisol response among police officers.
Fekedulegn-DB; Burchfiel-CM; Violanti-JM; Charles-LE; Andrew-ME; Hartley-TA; Miller-DB
Work, Stress, and Health 2009: Global Concerns and Approaches, San Juan, Puerto Rico, November 5-8, 2009. Washington, DC: American Psychological Association, 2009 Nov; :45
Objective: Research indicates shift work may lead to disruption of circadian rhythms and adverse health outcomes. Studies examining the influence of shift work on circadian rhythms, although few in number, have focused on hypothalamic-pituitary adrenal (HPA) axis dysregulation with the awakening cortisol response receiving particular attention as a marker of HPA axis activity. Most of these studies involve monitoring of a small sample of participants and rarely consider long-term shift work information. The objective of the current study was to evaluate how shift work, ascertained using daily long-term records, influences morning salivary cortisol levels in terms of the total hormonal excretion and the dynamics of awakening response over time, among police officers who represent a high stress occupation. Methods: Participants were a randomly selected group of police officers from the Buffalo, New York police department (n = 100; 42 females and 58 males). Work history data containing a day-by-day account of shifts for each officer, from May of 1994 to date of exam (2001-2003), were available for 96 of the 100 participants from payroll records of Buffalo police officers. The time that participants started work was used to determine shift; day shift if the start time ranged between 4 am and 11 am; afternoon shift if the start time ranged between 12 pm and 7 pm; midnight shift if the start time ranged between 8 pm and 3 am. Total hours worked as well as hours worked during day, afternoon and midnight shifts were computed for each participant. In order to take into account the length of time a participant was working, the computed hours were standardized to a weekly basis and the percent of total hours worked on each shift was calculated. Officers were then classified into one of the three shifts based on whichever shift had the largest percentage of hours worked for a given officer. Awakening cortisol measures were obtained from four salivary samples taken at 15 minute intervals upon first awakening (at awakening, 15, 30 and 45 minutes after waking). Previous assessment of the current study population showed that derived awakening cortisol parameters can be classified into two components; those that measure total hormonal excretion (average of the waking samples (AVE), the peak morning sample (PK) and total area under the curve (AUCG)) and those that measure the profile or pattern of cortisol over time (reactivity (RT), slope of the regression line fitted to the waking samples (SP), and area under the curve with respect to increase (AUCI)). These derived parameters were used as measures of awakening cortisol response in this study. The association of shift work with cortisol was examined by comparing mean values of cortisol parameters across the three shift work categories using analysis of variance and covariance. Multiple linear regression analyses relating the cortisol parameters with the continuous measure of shift work (% of hours on various shifts) and various covariates were also performed. Only officers with complete data on all four waking cortisol samples and time of collection of the samples were used for statistical analyses (n=65). Results: Salivary cortisol concentrations (nmol/liter ± SD) averaged across all four time points differed significantly among the day, afternoon and midnight shift workers (P = 0.0383); with midnight shift workers (10.8 ± 9.9) showing an attenuated awakening cortisol secretion compared with the afternoon (15.5 ± 9.6) or day (15.4 ± 10.4) shift. In contrast the pattern of cortisol secretion appeared not to be affected as no significant interaction effect (P = 0.1486) was found between time since awakening and shift work. This is consistent with the similar patterns of cortisol concentration over time across the three groups. Peak morning cortisol concentration (nmol/liter), although not significantly different among the groups (P = 0.070), was smaller for midnight shift workers (14.8 ± 12.8) than the afternoon (21.2 ± 13.5) or day (22.1 ± 16.3) shift workers. Total area under the curve (AUCG), in nmol/liter × minutes, also differed significantly among the three shift work groups (P = 0.041); again those in the midnight shift (500 ± 459) showed lower total area under the curve than those in the afternoon (759 ± 467) or day shift (745 ± 502). Adjustment for covariates (age, gender, education, smoking, alcohol consumption, physical activity and body mass index) had minimal influence on these associations. Conclusion: The results of this study show that midnight shift work is associated with decreased mean absolute level and total cortisol response on awakening, possibly indicating relatively greater dysregulation of total morning HPA axis activity for midnight shift workers.
Biological-effects; Biological-function; Biological-monitoring; Biological-rhythms; Biological-systems; Metabolic-rate; Metabolism; Police-officers; Quantitative-analysis; Shift-work; Sleep-deprivation; Sleep-disorders; Statistical-analysis
Desta B. Fekedulegn, PhD, National Institute for Occupational Safety and Health, Morgantown, WV, Biostatistics and Epidemiology Branch, Health Effects Laboratory Division, NIOSH, CDC, Morgantown, WV 26505
Services: Public Safety
Work, Stress, and Health 2009: Global Concerns and Approaches, San Juan, Puerto Rico, November 5-8, 2009