Bright Light Facilitates Circadiance Adaption Among Night Workers At An Oil PlatformSupported in part by The Research Council of Norway
June 24, 2001
Bjoern Bjorvatn, Goeran Kecklund and Torbjoern Aekerstedt
Introduction: Night workers complain of sleepiness, reduced performance, and disturbed sleep due to lack of adjustment of the circadian rhythm. In several studies, bright light treatment has been shown to fascilitate the adaptation to night work, so that alertness at night and sleep during the day improve (Czeisler et al. 1990; Dawson et al. 1995). So far, most of these studies have been done on simulated night work in a laboratory setting.
Method: We investigated the effects of bright light treatment at an oil platform in the North Sea. Seven workers completed the Karolinska Sleep/Wake Diaries for 14 days of consecutive night work and during the first week at home following the night shift period, first during a baseline recording without bright light exposure and then several months later during a trial with bright light. Bright light treatment was employed during the first 4 nights on night shift and the first four days at home to readjust the circadian rhythm. Bright light exposure was individually timed to phase delay of the endogenous rhythm, and the timing of bright light was changed from day to day in order to maximize the effects of the circadian clock. The workers were exposed to bright light (MiljoeLys AS, Norway; 10000 lux at 50cm distance) for 30 min each day. Following the adaptation and readaptation periods the workers subjectively indicated the number of days to adapt/readapt the circadian rhythm. They also rated these periods (1=much better than usual, 3=better than usual, 5=as usual, 7=worse than usual, 9=much worse than usual).
Results: Bright light treatment significantly reduced sleepiness at home (ANOVA, p<0.01), whereas sleepiness during night work showed a weaker reduction (p=0.07). Similar findings were seen on other rated paremeters. The number of days to adapt to night shift was not significantly reduced following bright light treatment (2.6+-0.4 vs. 3.1+-0.1), but the shift period with bright light was rated as better (3.1+-0.4 vs 5.0+-0.2, p<0.01, paired t-test). At home, the number of days to readapt back to day life was reduced with bright light (3.4+-0.5 vs 5.2+-0.5, p<0.01, paired t-test) and the readaptation was also rated as better (3.2+-0.3 vs 4.9+-0.3, p<0.05, paired t-test). Note that during baseline recordings the workers reported an adaptation to night work within a few days, whereas the readaptation back to day life at home was reported to take longer time (3.1+-0.1 vs 5.2+-0.5, p<0.01, paired t-test).
Conclusions: Bright light treatment for only 30 min per day seemed to facilitate adaptation to night work in the North Sea as well as readaptation back to day life following return home. The effect of bright light was especially pronounced at home, whereas during night work the effect was more modest. The reason for the modest effect of bright light at the oil platform ws probably that the workers adapted to night work within a few days even without bright light treatment. This is one of the few studies examining the effects of bright light treatment in a real life setting, and it shows that short exposure times may be efficient. This is important since 30 min of bright light exposure may be placed inside scheduled breaks, and thus may not compromise working time.
References: Czeisler CA, Johnson MP, Duffy JF, Brown EN, Ronda JM, Kronauer RE. N Engl J Med 1990; 322: 1253-9.
Dawson D, Encel N, Lushington K., Sleep 1995; 18: 11-21.
Sources of research report: Supported in part by The Research Council of Norway.
Want more information? Return to the research page here.