- Email: [email protected]
Shift type and season affect adaptation of the 6-sulphatoxymelatonin rhythm in offshore oil rig workers
Neuroscience Letters 252 (1998) 179–182
Shift type and season affect adaptation of the 6sulphatoxymelatonin rhythm in offshore oil rig workers R.G. Barnes a, M.J. Forbes b, J. Arendt a ,* a
Endocrinology and Metabolism Group, School of Biological Sciences, University of Surrey, Guildford, Surrey GU2 5XH, UK b Medical Department, Shell (UK) Exploration and Production, Aberdeen, UK Received 12 June 1998; received in revised form 7 July 1998; accepted 7 July 1998
Abstract Previously we have shown that the 6-sulphatoxymelatonin rhythm of oil rig workers on a 2-week night shift (1800–0600 h) adapts to the shift via a phase delay. We now report the findings of a study on two offshore drill crews working a 1 week day (1200–0000 h), 1 week night (0000–1200 h) swing shift. Urine samples were collected every 2–3 h throughout the subjective days, with over-sleep collections, for the measurement of 6-sulphatoxymelatonin by radioimmunoassay. One crew (n = 11), studied in November, showed no change in their 6-sulphatoxymelatonin rhythm during night shift. The other crew (n = 7), studied in March, showed a significant phase advance of the rhythm during night shift. The data indicate that both the type of shift and the season influence the direction and degree of adaptation. 1998 Published by Elsevier Science Ireland Ltd. All rights reserved
Keywords: Melatonin; 6-Sulphatoxymelatonin; Shiftwork; Circadian rhythm
There are many problems associated with night shift work, involving both the disruption of social activities and the desynchrony between internal biological clock timing and the forced regimen. Both short term problems (e.g. sleep deficiency, reduced alertness and reduced performance) and potential long term problems (e.g. coronary heart disease and diabetes) may be critically dependent on whether or not the worker adapts to the shift regimen. Therefore it is important to assess the degree of adaptation to a particular shift system in order to identify risk and provide potential treatment strategies (e.g. light exposure at night) if appropriate. While many studies have shown a lack of adaptation in night shift workers, our previous study showed that offshore oil rig personnel, working a 2-week, 12-h night shift (1800– 0600 h) and at a latitude of 61°N, were able to adapt their 6sulphatoxymelatonin (aMT6s) rhythms fully to the shift regimen via a phase delay [2]. This adaptation was surpris-
* Corresponding author. Tel./fax: +44 1483 259712; e-mail: [email protected]
ingly not influenced by seasonal differences in light exposure: the same rate and degree of phase shift was seen both in the presence (in summer) and absence (in winter) of morning and evening natural light exposure. Seasonality in humans results in a tendency for the melatonin rhythm to be phase delayed in winter compared to summer [6], especially in polar regions [3]. This is also seen in shiftworkers who avoid morning light and thus have a similar light exposure to that produced in winter [5,7]. Hence differences in adaptation, whether they be seasonal or not, are likely to depend on scheduling. We therefore conducted a similar study on a separate set of oil workers, working a 2-week ‘swing’ shift of 1 week days (1200–0000 h), one week nights (0000–1200 h) with a rapid changeover in between (rest 0000–0800 h, work 0800–1600 h, rest 1600–0000 h). We now report the results of this study which was conducted in both the winter and the spring. The subjects were recruited on a voluntary basis only, and the study protocol was approved by the University of Surrey’s Advisory Committee on Ethics. Two separate drill crews were studied on the same floating drilling rig (located in the North Sea, 61°N). One crew
0304-3940/98/$19.00 Published by 1998 Elsevier Science Ireland Ltd. All rights reserved PII S0304- 3940(98) 00585- 0
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R.G. Barnes et al. / Neuroscience Letters 252 (1998) 179–182
was studied in November (n = 11, aged 25–41 years, mean ± SEM 34.6 ± 2.1 years) and the other in March (n = 7, aged 25–48 years, mean ± SEM 32.6 ± 1.8 years). The shift regimen was identical for both crews. All personnel remained on the rig during their 2-week work period and went home for 2 weeks when on leave. Subjects were studied continuously throughout the 2-week work period. Light exposure was measured using a standard lux meter with a sensor placed at eye level. Measurements were taken on both the drill floor and pipe deck where the subjects worked, and also in the accommodation module, at the start and one hour before the end of both the day shift and night shift for each crew. Urine samples were collected every 2–3 h during wake periods, with one collection over the sleep period, for the whole two weeks. Subjects collected all urine produced during each period. The volume of each sample was recorded and a 5 ml aliquot was frozen until assay. The concentration of aMT6s in each sample was assessed by radioimmunoassay [1]. The interassay coefficients of variation were between 13.9 and 15.9% for the range 4.2–43.1 ng/ml. The values for each sampling period, expressed as ng/h, were used to calculate the rhythm peak (acrophase) by computerised cosinor analysis (program developed by D.S. Minors, Manchester University, UK). Values were only accepted if the fit to a cosine curve was significant (P , 0.05). Significant differences between mean daily acrophases for each crew were tested by one-way analysis of variance (ANOVA) with post-hoc testing (Duncan New Multiple Range) where day was the factor. Differences between the two crews were assessed by Student’s unpaired t-test applied to individual days. Subjective sleep logs were completed daily by the volunteers. These recorded subjective sleep onset and offset, latency, number and duration of awakenings, and sleep quality (10 cm visual analogue scale). The percentage of time actually spent asleep during lights out in bed was also calculated from these data to give sleep efficiency. Objective sleep measurements were assessed by using wrist activity monitors supplied by Cambridge Neurotechnology Ltd. Subjects wore the monitors on their non-dominant wrists continuously except when having a shower. The
Fig. 1. Average scotoperiods for (a) the November study and (b) the March study. Shaded bars represent sun down, white bars represent sun up and horizontal squared brackets represent the range of sunset and sunrise for the study periods. Information provided by Bristow Helicopters Operations, Safe Gothia, North Sea.
Fig. 2. Mean ± SEM daily aMT6s acrophase positions for the November drill crew (B) and the March drill crew (X). Day 1 is the first day on the rig and day 8 is the rapid changeover from day shift to night shift. Where error bars are not visible they are encompassed in the symbol.
monitors were set up by the computer program Sleep Watch Version 2.17 (Cambridge Neurotechnology Ltd.) to record the amount of movement in 1-min epochs. The program was then used to download the data via a serial port linked interface and calculate sleep parameters based on the amount of
Fig. 3. Mean ± SEM daily aMT6s acrophase positions for each crew superimposed on the shift schedule. Dark shaded bars represent time off the installation, light shaded bars represent free time and white bars represent the work shift period.
R.G. Barnes et al. / Neuroscience Letters 252 (1998) 179–182
Fig. 4. Mean ± SEM subjective sleep duration for both groups. Light shaded bars represent day shift and dark shaded bars represent night shift. *Significant difference (P = 0.005) between shifts.
movement measured. All sleep data was normalised before analysis by expressing data as individual percentages of day shift means. Comparisons between day shift and night shift sleep parameters were assessed by repeated measures ANOVA. During the work periods, the crew spent the majority of their time on the pipe deck (outdoors) or on the drill floor (indoors but with a large opening on one wall exposed to the natural environment). Therefore most of their work time was spent under natural light-dark conditions reinforced by artificial light during night shift. All personnel wore hard hats in the work areas which gave a large degree of shading from overhead light sources. Light exposure during November on night shift consisted of both artificial (cool white fluorescent) and natural light, ranging between 70 and 1400 lux. Exposure during March on night shift was a mixture of natural and artificial light, and ranged between 70 and 1800 lux. Artificial light exposure in the accommodation module was the same throughout the year and ranged between 100 and 450 lux. The bedrooms were light tight. Fig. 1 shows the average natural scotoperiods during each study. The daily aMT6s acrophases for both crews are shown in Fig. 2. In the November and March groups the day shift acrophases phase delay slightly, from a position of 0541 ± 0.38 h (mean ± SEM) and 0544 ± 0.47 to 0651 ± 0.29 and 0654 ± 0.56 h respectively, in line with the delay of the sleep and work periods. However, following the rapid change over (day 8), the March crew showed a significant (P , 0.05) phase advance from the day shift position to 0051 ± 1.70 h (mean ± SEM) by day 12. The November crew showed only a slight, but non-significant (P . 0.05), phase advance to 0506 ± 1.45 h (mean ± SEM) by day 14. The March crew acrophases were significantly different (P , 0.05) from the November crew during days 11–14. The relation between the acrophase positions and the shift
181
pattern is shown in Fig. 3. In both groups the acrophases remain in the work period during night shift. For all sleep parameters except subjective sleep duration, there were no significant differences (P . 0.05) between day shift and night shift in either group. Fig. 4 shows the mean subjective sleep durations for each group. Sleep duration is significantly (P = 0.005) shorter on night shift in the November group compared to day shift. The data clearly indicate a seasonal variation in adaptation to night shift in the particular shift regimen studied. This variation is most likely due to the differences in both the duration and intensity of natural light exposure between the two groups. Sunrise during March occurs approximately 2 h earlier than in November with a concomitant increase in light intensity. We consider that this early light exposure, falling mainly in the advance portion of the phase response curve [8], was sufficient to advance the melatonin rhythm in the March group. Similar results have been observed in light treatment studies on both normal day workers in temperate [4] and polar [3] regions. The reduced subjective sleep duration observed in the November group is likely to be due to the lack of circadian adaptation. This sleep loss is not seen in the March group who display aMT6s acrophases more in phase with the free time and sleep period. In conclusion, shift scheduling determines the degree and direction of circadian adaptation to night shift in offshore oil workers, with full adaptation observed in some circumstances. Seasonality is an important factor in certain shift regimens and hence should be taken into account when designing shift schedules. This work was supported by Shell (UK) Exploration and Production, and Stockgrand Ltd. (University of Surrey, UK). We would especially like to thank Sedco Forex for access to their rig and the volunteers for their involvement and efforts in an already difficult environment. [1] Aldhous, M.E. and Arendt, J., Radioimmunoassay for 6-sulphatoxymelatonin in urine using an iodinated tracer, Ann. Clin. Biochem., 25 (1988) 298–303. [2] Barnes, R.G., Deacon, S.J., Forbes, M.J. and Arendt, J., Adaptation of the 6-sulphatoxymelatonin rhythm in shiftworkers on offshore oil installations during a 2-week 12-h night shift, Neurosci. Lett., 241 (1998) 9–12. [3] Broadway, J., Arendt, J. and Folkard, S., Bright light phase shifts the human melatonin rhythm during the Antarctic winter, Neurosci. Lett., 79 (1987) 185–189. [4] Buresova, M., Dvorakova, M., Zvolsky, P. and Illnerova, H., Early morning bright light phase advances the human circadian pacemaker within one day, Neurosci. Lett., 121 (1991) 47– 50. [5] Eastman, C.I., Stewart, K.T., Mahoney, M.P., Liu, L. and Fogg, L.F., Dark goggles and bright light improve circadian adaptation to night-shift work, Sleep, 17 (1994) 535–543. [6] Illnerova, H., Zvolsky, P. and Vanecek, J., The circadian rhythm in plasma melatonin concentration of the urbanized man: the effect of summer and winter time, Brain Res., 328 (1985) 186– 189.
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[7] Koller, M., Ha¨rma, M., Laitinen, J.T., Kundi, M., Piegler, B. and Haider, M., Different patterns of light exposure in relation to melatonin and cortisol rhythms and sleep of night workers, J. Pineal Res., 16 (1994) 127–135. [8] Van Cauter, E., Sturis, J., Byrne, M.M., Blackman, J.D.,
Leproult, R., Ofek, G., L’Hermite-Baleriaux, M., Refetoff, R., Turek, F.W. and Van Reeth, O., Demonstration of rapid lightinduced advances and delays of the human circadian clock using hormonal phase markers, Am. J. Physiol., 266 (1994) E953–E963.
Shift type and season affect adaptation of the 6sulphatoxymelatonin rhythm in offshore oil rig workers R.G. Barnes a, M.J. Forbes b, J. Arendt a ,* a
Endocrinology and Metabolism Group, School of Biological Sciences, University of Surrey, Guildford, Surrey GU2 5XH, UK b Medical Department, Shell (UK) Exploration and Production, Aberdeen, UK Received 12 June 1998; received in revised form 7 July 1998; accepted 7 July 1998
Abstract Previously we have shown that the 6-sulphatoxymelatonin rhythm of oil rig workers on a 2-week night shift (1800–0600 h) adapts to the shift via a phase delay. We now report the findings of a study on two offshore drill crews working a 1 week day (1200–0000 h), 1 week night (0000–1200 h) swing shift. Urine samples were collected every 2–3 h throughout the subjective days, with over-sleep collections, for the measurement of 6-sulphatoxymelatonin by radioimmunoassay. One crew (n = 11), studied in November, showed no change in their 6-sulphatoxymelatonin rhythm during night shift. The other crew (n = 7), studied in March, showed a significant phase advance of the rhythm during night shift. The data indicate that both the type of shift and the season influence the direction and degree of adaptation. 1998 Published by Elsevier Science Ireland Ltd. All rights reserved
Keywords: Melatonin; 6-Sulphatoxymelatonin; Shiftwork; Circadian rhythm
There are many problems associated with night shift work, involving both the disruption of social activities and the desynchrony between internal biological clock timing and the forced regimen. Both short term problems (e.g. sleep deficiency, reduced alertness and reduced performance) and potential long term problems (e.g. coronary heart disease and diabetes) may be critically dependent on whether or not the worker adapts to the shift regimen. Therefore it is important to assess the degree of adaptation to a particular shift system in order to identify risk and provide potential treatment strategies (e.g. light exposure at night) if appropriate. While many studies have shown a lack of adaptation in night shift workers, our previous study showed that offshore oil rig personnel, working a 2-week, 12-h night shift (1800– 0600 h) and at a latitude of 61°N, were able to adapt their 6sulphatoxymelatonin (aMT6s) rhythms fully to the shift regimen via a phase delay [2]. This adaptation was surpris-
* Corresponding author. Tel./fax: +44 1483 259712; e-mail: [email protected]
ingly not influenced by seasonal differences in light exposure: the same rate and degree of phase shift was seen both in the presence (in summer) and absence (in winter) of morning and evening natural light exposure. Seasonality in humans results in a tendency for the melatonin rhythm to be phase delayed in winter compared to summer [6], especially in polar regions [3]. This is also seen in shiftworkers who avoid morning light and thus have a similar light exposure to that produced in winter [5,7]. Hence differences in adaptation, whether they be seasonal or not, are likely to depend on scheduling. We therefore conducted a similar study on a separate set of oil workers, working a 2-week ‘swing’ shift of 1 week days (1200–0000 h), one week nights (0000–1200 h) with a rapid changeover in between (rest 0000–0800 h, work 0800–1600 h, rest 1600–0000 h). We now report the results of this study which was conducted in both the winter and the spring. The subjects were recruited on a voluntary basis only, and the study protocol was approved by the University of Surrey’s Advisory Committee on Ethics. Two separate drill crews were studied on the same floating drilling rig (located in the North Sea, 61°N). One crew
0304-3940/98/$19.00 Published by 1998 Elsevier Science Ireland Ltd. All rights reserved PII S0304- 3940(98) 00585- 0
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was studied in November (n = 11, aged 25–41 years, mean ± SEM 34.6 ± 2.1 years) and the other in March (n = 7, aged 25–48 years, mean ± SEM 32.6 ± 1.8 years). The shift regimen was identical for both crews. All personnel remained on the rig during their 2-week work period and went home for 2 weeks when on leave. Subjects were studied continuously throughout the 2-week work period. Light exposure was measured using a standard lux meter with a sensor placed at eye level. Measurements were taken on both the drill floor and pipe deck where the subjects worked, and also in the accommodation module, at the start and one hour before the end of both the day shift and night shift for each crew. Urine samples were collected every 2–3 h during wake periods, with one collection over the sleep period, for the whole two weeks. Subjects collected all urine produced during each period. The volume of each sample was recorded and a 5 ml aliquot was frozen until assay. The concentration of aMT6s in each sample was assessed by radioimmunoassay [1]. The interassay coefficients of variation were between 13.9 and 15.9% for the range 4.2–43.1 ng/ml. The values for each sampling period, expressed as ng/h, were used to calculate the rhythm peak (acrophase) by computerised cosinor analysis (program developed by D.S. Minors, Manchester University, UK). Values were only accepted if the fit to a cosine curve was significant (P , 0.05). Significant differences between mean daily acrophases for each crew were tested by one-way analysis of variance (ANOVA) with post-hoc testing (Duncan New Multiple Range) where day was the factor. Differences between the two crews were assessed by Student’s unpaired t-test applied to individual days. Subjective sleep logs were completed daily by the volunteers. These recorded subjective sleep onset and offset, latency, number and duration of awakenings, and sleep quality (10 cm visual analogue scale). The percentage of time actually spent asleep during lights out in bed was also calculated from these data to give sleep efficiency. Objective sleep measurements were assessed by using wrist activity monitors supplied by Cambridge Neurotechnology Ltd. Subjects wore the monitors on their non-dominant wrists continuously except when having a shower. The
Fig. 1. Average scotoperiods for (a) the November study and (b) the March study. Shaded bars represent sun down, white bars represent sun up and horizontal squared brackets represent the range of sunset and sunrise for the study periods. Information provided by Bristow Helicopters Operations, Safe Gothia, North Sea.
Fig. 2. Mean ± SEM daily aMT6s acrophase positions for the November drill crew (B) and the March drill crew (X). Day 1 is the first day on the rig and day 8 is the rapid changeover from day shift to night shift. Where error bars are not visible they are encompassed in the symbol.
monitors were set up by the computer program Sleep Watch Version 2.17 (Cambridge Neurotechnology Ltd.) to record the amount of movement in 1-min epochs. The program was then used to download the data via a serial port linked interface and calculate sleep parameters based on the amount of
Fig. 3. Mean ± SEM daily aMT6s acrophase positions for each crew superimposed on the shift schedule. Dark shaded bars represent time off the installation, light shaded bars represent free time and white bars represent the work shift period.
R.G. Barnes et al. / Neuroscience Letters 252 (1998) 179–182
Fig. 4. Mean ± SEM subjective sleep duration for both groups. Light shaded bars represent day shift and dark shaded bars represent night shift. *Significant difference (P = 0.005) between shifts.
movement measured. All sleep data was normalised before analysis by expressing data as individual percentages of day shift means. Comparisons between day shift and night shift sleep parameters were assessed by repeated measures ANOVA. During the work periods, the crew spent the majority of their time on the pipe deck (outdoors) or on the drill floor (indoors but with a large opening on one wall exposed to the natural environment). Therefore most of their work time was spent under natural light-dark conditions reinforced by artificial light during night shift. All personnel wore hard hats in the work areas which gave a large degree of shading from overhead light sources. Light exposure during November on night shift consisted of both artificial (cool white fluorescent) and natural light, ranging between 70 and 1400 lux. Exposure during March on night shift was a mixture of natural and artificial light, and ranged between 70 and 1800 lux. Artificial light exposure in the accommodation module was the same throughout the year and ranged between 100 and 450 lux. The bedrooms were light tight. Fig. 1 shows the average natural scotoperiods during each study. The daily aMT6s acrophases for both crews are shown in Fig. 2. In the November and March groups the day shift acrophases phase delay slightly, from a position of 0541 ± 0.38 h (mean ± SEM) and 0544 ± 0.47 to 0651 ± 0.29 and 0654 ± 0.56 h respectively, in line with the delay of the sleep and work periods. However, following the rapid change over (day 8), the March crew showed a significant (P , 0.05) phase advance from the day shift position to 0051 ± 1.70 h (mean ± SEM) by day 12. The November crew showed only a slight, but non-significant (P . 0.05), phase advance to 0506 ± 1.45 h (mean ± SEM) by day 14. The March crew acrophases were significantly different (P , 0.05) from the November crew during days 11–14. The relation between the acrophase positions and the shift
181
pattern is shown in Fig. 3. In both groups the acrophases remain in the work period during night shift. For all sleep parameters except subjective sleep duration, there were no significant differences (P . 0.05) between day shift and night shift in either group. Fig. 4 shows the mean subjective sleep durations for each group. Sleep duration is significantly (P = 0.005) shorter on night shift in the November group compared to day shift. The data clearly indicate a seasonal variation in adaptation to night shift in the particular shift regimen studied. This variation is most likely due to the differences in both the duration and intensity of natural light exposure between the two groups. Sunrise during March occurs approximately 2 h earlier than in November with a concomitant increase in light intensity. We consider that this early light exposure, falling mainly in the advance portion of the phase response curve [8], was sufficient to advance the melatonin rhythm in the March group. Similar results have been observed in light treatment studies on both normal day workers in temperate [4] and polar [3] regions. The reduced subjective sleep duration observed in the November group is likely to be due to the lack of circadian adaptation. This sleep loss is not seen in the March group who display aMT6s acrophases more in phase with the free time and sleep period. In conclusion, shift scheduling determines the degree and direction of circadian adaptation to night shift in offshore oil workers, with full adaptation observed in some circumstances. Seasonality is an important factor in certain shift regimens and hence should be taken into account when designing shift schedules. This work was supported by Shell (UK) Exploration and Production, and Stockgrand Ltd. (University of Surrey, UK). We would especially like to thank Sedco Forex for access to their rig and the volunteers for their involvement and efforts in an already difficult environment. [1] Aldhous, M.E. and Arendt, J., Radioimmunoassay for 6-sulphatoxymelatonin in urine using an iodinated tracer, Ann. Clin. Biochem., 25 (1988) 298–303. [2] Barnes, R.G., Deacon, S.J., Forbes, M.J. and Arendt, J., Adaptation of the 6-sulphatoxymelatonin rhythm in shiftworkers on offshore oil installations during a 2-week 12-h night shift, Neurosci. Lett., 241 (1998) 9–12. [3] Broadway, J., Arendt, J. and Folkard, S., Bright light phase shifts the human melatonin rhythm during the Antarctic winter, Neurosci. Lett., 79 (1987) 185–189. [4] Buresova, M., Dvorakova, M., Zvolsky, P. and Illnerova, H., Early morning bright light phase advances the human circadian pacemaker within one day, Neurosci. Lett., 121 (1991) 47– 50. [5] Eastman, C.I., Stewart, K.T., Mahoney, M.P., Liu, L. and Fogg, L.F., Dark goggles and bright light improve circadian adaptation to night-shift work, Sleep, 17 (1994) 535–543. [6] Illnerova, H., Zvolsky, P. and Vanecek, J., The circadian rhythm in plasma melatonin concentration of the urbanized man: the effect of summer and winter time, Brain Res., 328 (1985) 186– 189.
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R.G. Barnes et al. / Neuroscience Letters 252 (1998) 179–182
[7] Koller, M., Ha¨rma, M., Laitinen, J.T., Kundi, M., Piegler, B. and Haider, M., Different patterns of light exposure in relation to melatonin and cortisol rhythms and sleep of night workers, J. Pineal Res., 16 (1994) 127–135. [8] Van Cauter, E., Sturis, J., Byrne, M.M., Blackman, J.D.,
Leproult, R., Ofek, G., L’Hermite-Baleriaux, M., Refetoff, R., Turek, F.W. and Van Reeth, O., Demonstration of rapid lightinduced advances and delays of the human circadian clock using hormonal phase markers, Am. J. Physiol., 266 (1994) E953–E963.