Journalof PsychosomaticResearch,Vol. 20, pp. 479 to 484. PergamonPress, 1976. Printedin Great Britain.

EXPOSURE TO NIGHT WORK: SERUM GASTRIN REACTIONS, PSYCHOSOMATIC COMPLAINTS AND PERSONALITY VARIABLES T.

AKERSTEDT*

and T.

THEORELL~

(Received 11 February 1976) Abstract-Seventeen dayworking railway repair men were subjected to a three week period of night work. Before, during, and after the night work period blood samples were obtained which were analysed with respect to content of gastrin. For corresponding weeks were obtained self-ratings of psychosomatic complaints concerning sleep, mood, gastric functioning and other problems. The subjects also filled out the Eysenck Personality Inventory scales of neuroticism and extraversion. Gastrin levels decreased during the night work period but returned afterwards although the variance of the latter was greatly increased. Psychosomatic complaints increased during night weeks. Correlation analysis showed that decreases in gastrin levels from before to after the night period was associated with increases in psychosomatic complaints. Also, the decrease in gastrin levels was found mainly among subjects with a higher degree of neuroticism before entering night work. EPIGASTRIC discomfort reflecting gastrointestinal dysfunction is a frequent complaint in connection with exposure to periods of night work and irregular work hours [l-3] The mechanism behind this association is unknown. One way of studying possible mechanisms in the relation between changes in circadian patterns of activity and gastric function is to follow longitudinally changes in psychological and physiological variables related to gastric function in subjects who go through periods of day and night work. A physiological variable of possible interest in this context is the serum level of the hormone gastrin which stimulates gastric acid secretion cf. [4] and also appears to exhibit a circadian variation [5]. As circadian rhythms in general are greatly disturbed by changes in the rest-activity patterns [6] this might also be the case for gastrin. Gastric functioning is intimately related to the emotional state of the individual [7], thus also personality variables may be of interest in a study of shift workers, particularly as Lund [8] has shown that high scorers on inventories measuring neuroticism and psychosomatic tendencies more often exhibit desynchronized (disturbed) circadian rhythms. The present study focusses on changes beforeduring-after night work of serum gastrin levels and psychosomatic complaints in subjects exposed to a three week period of night work. The purpose was to investigate whether changes in gastric level were related to psychosomatic complaints or personality variables. Other aspects of this study have been reported elsewhere [9].

METHOD The participants consisted of 17 clinically healthy railway workers, with a mean age of 36 yr (range 18-60). All were regular day workers with only an occasional earlier experience of night shifts. The work task consisted of replacing rail and was physically moderately heavy. Day work was carried out between 0730 and 1630 hr and night work between 2330 and 0730 hr. Figure 1 gives the temporal layout of the shift schedule and measurements. Before the study the subjects had experienced three weeks of night work and a four week vacation. The former served as a training period with respect to some of the difficulties of performing the work task in relative darkness. Blood specimens were obtained twice daily at 0700 hr (I) and 1300 hr (II) during day work before and after the three weeks of night work (weeks 3 and 7). Two samples were also obtained during the *Laboratory for Clinical Stress Research, Karolinska Institute and iDepartment of Medicine, Karolinska Institute at the Seraphimer Hospital. Requests for reprints to: T. Akerstedt, Laboratory for Clinical Stress Research, Fack, S-104 01 Stockholm 60, Sweden. 479

T. AKERSTEDTand T. THEORELL

480

ntroduction of shift work schedule

FIG. 1. Temporal lay-out of the investigation.

second week of night work (week 5) at 2300 hr (II) and 0600 hr (I). Samplings took place in the first half of each working week with a constant schedule for each subject. No manual work had been performed before the first sample of each pair. The subjects had been instructed to be strictly fasting before the sampling. Before the first sample during day shift it was possible to obtain 10 hr of fasting. Before the first sample during night shift 6 hr of fasting were obtained. Up to the second sample the subjects were kept fasting for 5-6 and 6-7 hr, respectively. The blood specimens were centrifuged immediately after cooling and then frozen. The concentration of gastrin was measured by a radio-immunoassay [lo]. The radioimmunological gastrin kit was obtained from Johnson & Johnson, Departement des Elements, Gif-sur-Yvette, France. For duplicate samples a correlation of r = 0.97 was obtained, i.e. total common variance reached 94% (rz). Before the night work experience the subjects also filled out the Eysenck Personality Inventory [1 1, 121 and indices of neuroticism and introversion were calculated for each person. Measurements of psychic and psychosomatic complaints were obtained each week by the use of self-administered questionnaires in which the subjects were asked to rate on a four point scale the frequency of occurrence (never to often) of various psychosomatic symptoms experienced during the preceding week. Each item was scored from 1 to 4, the latter indicating fewer complaints.Through factor analysis three clusters (indeces) of complaints were obtained: Sleep-mood complaints (SM), gastric complaints (G) and a “remaining” group of complaints (R). “SM” was composed of the following items: difficulties to fall asleep, difficulties to retain sleep, fatigue, restlessness, anxiety, apathy and depression. “G” comprised the items: epigastric pain, diarrhoea, flatulence, constipation, heart burn and lack of appetite. “R” comprised headache, dizziness, rapid heart beat, and difficulties in breathing. As intercorrelations between the indeces were high, a combined total score (TC) was also computed. Reliabilities in terms of Cronbachs alpha were 0.90, 0.63, 0.63 and 0.85 respectively. To obtain measures of change, the ratio before/during nightwork and before/after nightwork were computed for serum gastrin and each of the psychosomatic complaint subindeces. Thus values greater than 1 denotes a decrease in the variable over time. Variation over weeks was analysed through one-factor analysis of variance for repeated measurements according to Winer ([13], pp. 105-l 11,135). Relations between variables were analysed through correlation analysis. For the latter were used ratings only for the three weeks for which gastrin measurements were obtained. RESULTS

Variation over weeks No significant difference

was observed between the mean levels of gastrin at test occasions I and IT, respectively. In the following, all gastrin computations will, therefore, be based on means of I and It. The analysis of variance (see Fig. 1) revealed a significant variation over time for the SM index only (F = 3.1, df = 6/96, p < 0.01). Orthogonal comparisons for trend yielded a significant quadratic trend for the same index (F = 10.3, df = l/16, p < O-01). Thus there was a moderate but significant increase of complaints during night work. (Lower scores = more complaints.) Gastric complaints showed a similar tendency which was significant on the 10% level only.

Serum gastrin reactions, psychosomatic

complaints and personality variables

481

weeks FIO. 2. Mean values of gastrin levels and complaint

scores before, during and after nightwork.

The gastrin variation was not subjected to an analysis of variance as the variances differed greatly between weeks. Thus the variance after the night weeks (w 7) greatly exceeded that of the other two weeks (p < 0.001, F-test for variances, dependent measures). However, the decrease from before (w 3) to during night week (w 5) was significant (p < 0.05, t-test, dependent measures). After night work (w 7) the gastrin level rose to its initial value. Although the decrease from (w 3) to (w 5) was significant, values still remained within the normal range. On the personality inventory mean score and standard deviations were for Neuroticism 7.3 f 5.16 and for Extraversion 11.75 & 2.9. Correlations between serum gastrin, psychosomatic complaints and personality traits See Table 1. Gastrin levels correlated poorly with changes in complaint scores and personality variables, the only significant correlations being found for gastrin levels after night work. However, when before and after levels were combined to a ratio reflecting change in level, correlations strongly increased, i.e. it was the relative change in gastrin level from before to after night work that was correlated with the psychological parameters. Neuroticism exhibited a high negative correlation with the change before-after in gastrin level, i.e. subjects who rated high in Neuroticism (low score) did not return to pre-night work levels to the same extent as subjects low in Neuroticism (high score). Instead they retained the low level found in night work. (It should be observed that in order to obtain the EPI scores in analogue with the self-ratings of psychosomatic complaints the usual scoring of the EPI has been reversed for the computation of correlation coefficients, i.e. in the present study low scores indicate a high degree of the characteristic). For two of the psychosomatic complaint scores (SM & R) both the before/after and the before/during ratios correlated significantly with the before/after change in

482

T.

AKERSTEDT

and T. THEORELL

TABLE~.---CORRELATIONSBETWEENGASTRINVARIABLES(AVERAGEOFIANDII)ONTHEONEHANDAND COMPLAINT SCORES, NEUROTICISM AND INTROVERSION ON THE OTHER. COEFFICIENTS SIGNIFICANT AT THE 0.05 LEVEL OR BETTER (TWO TAILED) ARE UNDERLINED. FOR PERSONALITY VARIABLES AND COMPLAINT SCORESLESSOFTHEPROPERTY/FEWERCOMPLAINTSYIELD HIGHERVALUES

Gastrin before/during Gastrin before/after Gastrin befbre

.ti3

.03

.35

.30

-.lO

.69 --

.49

.fJ8 -.21

.21

.22

-.x

.46

,. 10

.08

.46

.40

.40

.13

.g

.a_I -.z

.28

-.23

-.04

.04

.18

Gastrin during

.04

.oo

-.lO

.18

-.37

-.28

-.40

-.32

-.02

Gastrin after

.54 -

-.ll

-.40

-.27

L.03

-.25

-.58 --

-.50

.37

-.34

-.18,

-.83 .-.Ol

-.81 -.06

.25

.Ol

.z

.43

gastrin level such that individuals with high psychosomatic ratios also obtained high gastrin ratios. This means that individuals who decreased most in well-being did not return to their initial gastrin level after night work. The change in gastric complaints, however, correlated rather poorly with the gastrin variables, even if the correlation between change in gastric complaints before/during and gastrin change before/during came very close to significance. Also for the absolute level of the total complaint (TC) score the main relation was found with the change in gastrin level before/after. Correlation coefficients were also computed without using the mean of the gastrin values (I + I I) but instead treating each value separately. These coefficients were very similar to those based on the mean and are, therefore, not reported. “Gastric complaints” was also divided into those items presumably indicative of increased acid secretion (e.g. “epigastric pain” and “heartburn”) and those presumably indicative of decreased acid secretion (“loss of appetite” and “flatulence”). The analysis of these individual items failed to show significant relations with the gastrin levels although tendencies in the expected direction were observed. Only a small number of subjects indicated each symptom. DISCUSSION

The analysis of variance indicated a moderate increase of mainly sleep-mood complaints during the weeks of nightwork. The gastrin level was reduced, also during night weeks. However, previous studies have demonstrated circadian variations in serum gastrin levels [5]. It appears that the serum gastrin levels follow the same pattern as the activation level of the organism as reflected e.g. in the excretion of catecholamines in the urine [14]. Thus, the decreased gastrin levels during night work may merely reflect the normal circadian variation. Before and during night work the variance of gastrin was moderate in spite of a significant change in means. After night work the variance was significantly raised in spite of the mean being close to the mean before night work. This suggests a great interindividual variation in the behavior of the gastrin levels, i.e. after night work

Serum gastrin reactions, psychosomatic complaints and personality variables

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some individuals greatly exceeded their value before night work while others failed to reach that level. The correlation analysis suggests that it is the change in gastrin level from before to after the night weeks that is related to personality and self-rating variables. The most important component of the gastrin ratio was the “aftervalue” which was also found to have a significantly increased dispersion of gastrin values. It was hypothesized that the gastrin before/after ratio would have been significantly related to the gastric complaints ratio for the corresponding weeks. These correlations were not significant and the hypothesis thus not supported, although tendencies in the expected direction were seen. The corresponding correlations with the ratios of the two other complaint scores, on the other hand, reached well beyond significance. Thus a decrease of the gastrin level before/after was accompanied in a non-specific way by a decrease in well-being. Of particular interest is the negative sign of the correlation coefficients. From the literature psychosomatic problems were expected to be associated with increases in acid levels and gastrin levels cf. [7]. Furthermore neuroticism is generally associated with increase in physiological activation and a subsequent “non-decrease” from this level, cf. [12]. In the present study the relations were reversed, i.e. after the decrease during night work they assumed the character of a “non-reincrease” to day work. Thus it appears that the gastrin changes in night work may reflect a carry-over of night work effects on circadian rhythms into the subsequent day work period. This carry-over then is found primarily among those individuals whose personality makeup includes more of neurotic and psychosomatic traits. With psychosomatic discomfort being related to a lowered gastrin level it is also of interest to note that an important function of gastrin is its role in the regulation of the tonus of the lower esophageal sphincter [15]. Thus, a relative lack of gastrin may create inadequate pressure regulation in the stomach. While the changes in gastrin levels observed in the present study were of a nonpathological magnitude, they may still be of significance in a long-term perspective. The main contribution of the present study is the suggestion that gastrin change in shiftwork may be related to psychosomatic discomfort and also to be partly a function of the personality characteristics of the individual. Acknowledgements-Biochemical analyses were performed by Miss K. Thor& and Miss I. Gustavsson. L. Torsvall, B.A., and S. Bergenstrahle, B.A., participated in the data collection and data analysis. The authors are indebted to Professors L. Levi. J. Friibera. S. Emas. and S. Wolf for constructive criticism of the manuscript. The present work.was supported by giants from the Swedish Work Environment Fund and the Swedish Medical Research Council (No. 4316) and was made possible through the cooperation of the subjects, their labor union (Statsanstilldas fiirbund) and the employer (Statens Jlrnvggar). REFERENCES 1. AANONSENA. Shift Work and Health. Universitetsforlaget, Oslo (1964). 2. ANDERSENJ. E. Three-Shif Work. A Socio-Medical Survey. Vol. I + II. Teknisk Forlag, Copenhagen (1970). 3. MENZELW. Menschiiche Tag-Nacht-Rhythmik und Schichtarbeit. Schwabe, Base1 (1962). 4. THOMPSONJ. C. Gastrin and gastric secretion. Ann. Rev. Med. 20, 291 (1969). 5. MOOREJ. G. and WOLFE M. The relation of plasma gastrin to the circadian rhythm of gastric acid secretion in man. Digestion 9,97 (1973). 6. ASCHOFFJ., HOFFMANK., POHL H. and WEVER R. Re-entrainment of circadian rhythms after phase-shifts of the Zeitgeber. Chronobiologiu 2, 23 (1975).

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7. WOLF S. The Stomach. Oxford University Press, Oxford (1965). 8. LUND R. Personality factors and desynchronization of circadian rhythms. Psychosom. Med. 36,

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