Permanent night work alters characteristics of circadian rhythm of rest–activity in human subjects

The objective of this study was to explore the impact of permanent night shift on rest–activity rhythm in 20 randomly selected male permanent night workers, employed in a local newspaper printing office. The machine operators performed their job from 20:00 to 04:00 and the computer operators from 18:00 to 02:00 every day. The night workers availed one-day rest after working six consecutive days. Twenty-one age- and gender-matched day workers were also studied for comparison of rhythm parameters. In each subject rest–activity rhythm was monitored non-invasively by using Actiwatch (AW64 Mini Mitter Co. Inc., USA). Data were gathered at one-minute intervals for seven consecutive days. In addition, all subjects also responded to the morningness-eveningness questionnaire (Horne and Ostberg's MEQ). Data were stored in the form of records and analyzed with the help of Actiware sleep software, Cosinor rhythmometry, Power spectrum analysis, Autocorrelation, ANOVA and Duncan's multiple range test, t-test and descri...