INFLUENCE OF SHIFT WORK ON TIME AND FREQUENCY OF MEAL TAKING

Transcription

1 J. Human Ergol.,1: , 1972 INFLUENCE OF SHIFT WORK ON TIME AND FREQUENCY OF MEAL TAKING Kazuo TAKAGI Institute for Science of Labour, Kawasaki, Japan Effect of shift work on time and frequency of meals of workers at an iron works, a chemical factory, and five textile factories were investigated, and the results were compared with two-meal habits in former times. A meal was defined as an occasion when two or more kinds of food were taken. Meal time proved to be affected by an evening or night shift, resulting in a decrease of meal frequency among up to nearly half the workers. Many tended to omit either breakfast or a midday meal, but to take the evening meal at regular hours. Few shift workers increased meal frequency. Female double-day shifters generally had three meals a day, though the midday meal had to be delayed by the morning shift. Bibliographical studies on meal habits in the early modern period in Japan demonstrate that a change from two to three meals a day was accomplished in the 18th century by adding a third meal following the late afternoon meal, the latter then becoming the chief meal at midday. Modern industrial work has helped establish the three-meal habit in accordance with the lengthening of activity time toward the night hours, the chief meal being taken in the evening. It remains doubtful, therefore, whether the two meals of modern shift workers supply enough nutrients. At the present time Japanese people generally take three meals a day. As a rule breakfast is comparatively light and simple, the menu changing very little from day to day. In the evening they usually take the chief meal of the day which includes more dishes and has more variety than other meals. In the case of daily workers, a light midday meal is taken during a lunch break which is homemade or served by the food service facilities on the premises. The threemeal habit thus seems firmly established in our modern way of life. Among shift workers, however, the regular meal habit may be affected not only by changes in times of activity but also by disturbances related to biological circadian rhythm. Although there have been many studies on changes of the Received for publication October 19,

2 196 K. TAKAGI circadian rhythm in shift work, we have little information so far on how shift work influences meal taking, especially with respect to the three-meal habit. The influence may be different according to the type of shift rotation, for example, between three-shift continuous operation in metallurgic and chemical industries and the two-shift systems common in mechanical and textile industries. It is also postulated that individual variations in time and frequency of meals are magnified by shift work. Attention should be paid to those possible deviations from the usual threemeal habit among shift workers, since they may have adverse effects on nutrition intake. It will be of interest to compare those deviations with the older habits observed before the modern three-meal habit was established. We have discussed the influence of shift work on meal habits based on field investigations (TAKAGI and KOIZUMI, 1963; TAKAGI et al., 1967; SATO and TAKAGI, 1972). The present paper attempts to summarize the results of these investigations, showing how the meal habits change among typically rotated shift workers, and will discuss the implications the regular three-meal habit may have for nutrition. METHOD A questionnaire form on which 24-hour time scales with 5-minute intervals were printed was used to record times of sleeping, work, and meals. A meal was defined as being when two or more kinds of food were taken at the same time. No meal was recorded when only one kind of food was taken. The recordings were obtained from 111 married and 301 unmarried men in an iron works, 130 married and 10 unmarried men in a chemical factory, and 724 women and 59 men in five textile factories. All the subjects at the iron works and the chemical factory were rotated by the three-shift system, and their duty hours were , ,00, in the iron works and , , in the chemical factory. The textile factories rotated female workers by the same double-day shift system, the duty hours being and 13, In these factories the male workers also worked nightshift hours from to Recordings on the days of shift change were not included. Percentage of workers who were either taking a meal or lying in bed in every half-hour period was calculated. Bibliographical studies were then conducted in order to compare the results with the dietary customs of earlier periods in Japan before the daily three-meal habit in its present form became the rule. RESULTS Percentage distributions of the number of meals taken on days of various shifts are given in Table 1. During the day-shift period % of the factory

3 INFLUENCE OF SHIFT WORK ON MEAL TAKING 197 Table 1. Percentage distribution of meal frequency per day in various shift periods. workers had meals three times a day. On days of the other shifts, the percentage of workers taking meals only twice or once a day markedly increased. Nearly half of the unmarried iron workers had less than three meals when they worked night shifts and on holidays. Even married workers reduced the meal frequency to less than three on about 40% of night-shift days. The chemical factory was conspicuous in that its married workers tended to have three meals in their nightshift periods while nearly half of them had only two meals in evening-shift periods. On both shifts most of the double-day shift workers at the textile factories kept to their three daily meals, though the percentage of workers having less than three meals doubled on afternoon-shift days. It is worth noting that while meal frequency was decreased by shift work in many cases it was also increased in a considerable number of cases. More than half of the male shift workers in the textile factories had four meals on their nightshift days. The number of workers taking four meals also increased during the evening-shift period at the iron works. In general there were found few workers who had only one meal a day, but their percentage was shown to increase on the evening or night shift. For three-shift workers except male textile workers, the average meal frequency per day was 2.90, 2.79 or 2.63 on days of day shift, evening shift, or night shift, respectively. For female double-day shift workers the average

4 198 K. TAKAGI Fig. 1. Rate of workers sleeping or at meals in each half-hour period on days of day, evening, and night shift of an iron works. Married; Sleep, Meal. Unmarried; Sleep, Meal.

5 INFLUENCE OF SHIFT WORK ON MEAL TAKING 199 Fig. 2, Rate of workers sleeping or at meals in each half-hour period on days of day, evening, and night shift of a chemical factory. Married; Sleep, Meal. Unmarried; Sleep, Meal.

6 200 K. TAKAGI frequency was 2.98 on days of morning shift and 2.93 on days of afternoon shift. Figure 1 shows the temporal variations in the rate of iron workers sleeping or at meals in each half-hour period for different shift periods. As shown in the figure, breakfast before the day shift was taken earlier than in the case of ordinary citizens, due to the early starting time of the shift. Married men took breakfast somewhat earlier than the unmarried. The midday meal was taken during the recess, while the time of the evening meal extended over several hours from to 22.00, especially among the unmarried. Compared with these dayshift patterns, the distribution of meals on days of evening or night shift showed Fig. 3. Rate of female workers sleeping or at meals in each half-hour period on days of morning and afternoon shift of five texitle factories., Sleep;, Meal.

7 INFLUENCE OF SHIFT WORK ON MEAL TAKING 201 a completely different pattern. On the day of an evening shift both married and unmarried men got up fairly late in the morning. Only a small part of them were at table at regular breakfast hours and many got up just before the midday meal. Supper was taken during a recess at the usual time, though about 20 of them took a late meal again at around after the end of the shift. During the night shift they took a meal in the middle of their working hours, which should correspond to lunch of a day shift. After work, breakfast was taken at home at around 8.00, later than the breakfast time of a day shift. After breakfast they went to bed, and because of the daytime sleep the lunch time disappeared except for some unmarried workers. As the times of rising varied greatly, the times of the evening meal covered the whole evening period. Similar results were obtained for shift workers at the chemical factory, as shown in Fig. 2. On day-shift days they were at meals at about the same hours as iron workers, though in fact breakfast time was a little later than for the latter. The breakfast time of evening-shift workers extended over several hours according to their different rising times, so that no distinct lunch time could be found. Their night-shift pattern was a little different from that of the iron workers, since the meal which they took during the shift was supplied in the early morning as a kind of breakfast. Returning home about one or two hours after eating that breakfast, some of them went to bed, while most of them stayed up and waited for the midday meal. They had supper around On the average they were in bed for about 6.5 hr, that is, less than the tlight-shift workers of the iron works. The distribution of the meal times of female textile workers was very characteristic for both the morning and afternoon shifts, as illustrated in Fig. 3. They Fig. 4. Rate of male workers or their wives sleeping or at meals on a day of night shift of textile factories. Husband; Sleep, Meal. Wife; Sleep, Meal.

8 202 K. TAKAGI worked the morning shift from 5.00 in the morning and had breakfast during the recess. They took a midday meal at about after they got off their shift, the interval between breakfast and the midday meal being nearly six hours or more. A few of them lay down for a nap after the meal. Supper time commenced at about and extended to as late as By about 80% of them were asleep, some remaining awake until midnight. On afternoon-shift days these female workers had a shorter interval between breakfast and lunch and a much longer interval between lunch and supper, in marked contrast to the morning shift. Only few of them took a light night meal after the afternoon shift. The hourly pattern of sleeping and meal taking of male night-shift workers of the textile factories shown in Fig. 4 resembled that for the night-shift days of the iron workers, the meal during the shift being taken at midnight. After returning home most of them had breakfast and then went to bed. About half of them got out of bed by noon to take a midday meal. After the evening meal taken at regular hours, some of them slept again before the night shift began. DISCUSSION It is seen that meal times varied greatly with the change in shifts. The findings from the female double-day shift workers clearly demonstrate that the time of meals as well as intervals between meals was altered to a considerable degree in accordance with the work rules for the shifts even though the workers kept rather strictly to the three-meal habit. Their work rules were set up to make full use of the working hours permitted by the Labor Standards Law, which forbids women to work at night from The results of the present study also indicate that the time of breakfast or the midday meal is more liable to be affected in all types of shift rotation than the time of the evening meal. This seems to be induced by the transfer of the rising time in accordance with the reduction of sleeping hours in periods of irregular shifts. The shift workers tended to change the frequency of meals per day especially on days of evening and night shifts, while during the day-shift period they adhered to the three-meal custom. A few people were found who increased the number of meals to four, but a reduction of the number of meals was far more frequent. It often happens that either breakfast or a midday meal is omitted or both of them are amalgamated into one, while the evening meal has a tendency to be taken at regular supper hours. The extensive alterations of meal-taking habits among shift workers and especially the reduction of the number of meals would affect the quantity as well as the quality of nutrients taken. So far as the frequency of meals is concerned, however, the scientific basis of the three-meal habit which is so common nowadays among ordinary day workers is not necessarily clear. The author has tried to study

9 INFLUENCE OF SHIFT WORK ON MEAL TAKING 203 the dietary habits of former ages and found that the three-meal habit has not always been conventional (HOSOKAWA, et al., 1971). In Japan from about the beginning of the 18th century, three meals used to be taken per day by town people. Before that time it was the custom of nearly all the Japanese to have a meal twice a day, and only heavy muscular workers such as carpenters or stonemasons had a mid-meal between breakfast and the evening meal. Generally speaking, breakfast was taken at about or sometimes at around noon and the work before breakfast was called asa-shigoto meaning morning work. The evening meal which was actually a late afternoon meal used to be at about It will be important then, in understanding the change of dietary customs, to investigate in what manner the third meal came into the two-meal custom; was the third meal put between the customary two meals or was it added as an extra meal following the two meals? Nanpo Oota ( ), a famous writer of the Edo period, wrote in his book Ichigon Itto (Giving an answer to each question), "the third meal was added after the evening meal and that is a simple and plain meal, and there is frequently the fourth meal in the late evening of autumn." Tanehiko Ryutei ( ), another famous writer of the Edo period, wrote in his book, "it is interesting that the meal taken at midday is called an evening meal and the meal taken in the evening is called a night meal." From these references it may be ascertained that the third meal came after the customary two meals, instead of being put between them. This would have been the reason why the third meal was simpler than the morning or evening meals which had long been taken. DRUMOND and WILBRAHAM (1971), in Englishman's Food, said that in England in the 16th century people took meals three times a day, and that in the 17th century breakfast was taken from 6 to 7 o'clock and the chief meal of the day, dinner, was eaten at about midday. Menus at workhouses and hospitals of that time were also noted by him. According to this note, the meal at midday was actually called dinner, beef being served, while in the evening only bread and cheese were served. At present Japanese have their chief meal in the evening, but at the beginning of the 20th century there still remained the custom of having the chief meal at midday in almost all farmers' and town merchants' families. The transfer to the three-meal habit seemed to be induced by the development of modern industries, which required long working hours and a short lunch recess. Then office and factory workers brought a lunch box with them. This reminds one of the European tradition of spending over two hours for the midday meal recognized as the dinner of the day. In the Japanese language meals are simply named morning meal, midday meal, and evening meal, which contrasts with the European names expressing the character of each meal, such as breakfast, dinner, and supper in En-

10 204 K. TAKAGI gush, petit dejeuner, dejeuner, diner and soupeur in French, or.fruhstuck, Mittagessen and Abendbrot in German, etc. Mittagessen can also mean dinner. These facts suggest that the change of daily meal frequency from two to three was in general introduced through addition of the third meal following the second meal, so that the third meal was simpler than the other two. When the industrialized way of life began to expand in Japan, the day's chief meal shifted from midday to evening. The increase of caloric consumption of workers did not necessarily give rise to the new habits of increased meal frequency; because if this had been the main cause, the third meal would have been put into the space between the two meals. The addition of the third meal is assumed to have been produced by the lengthening of the daily activity time as a result of the development and popularization of lighting equipment. In the case of modern shift work, meal taking is disturbed mostly in the daytime, and not in the evening. The omission of breakfast or even of a midday meal is common among many evening- or night-shift workers, while there are found few cases of workers who skip an evening meal. This seems to apply to various types of shift rotation, irrespective of the difference in working hours, though further investigations are needed in this respect. It is presumed that the acquisition of the circadian rhythm and the long meal habit might lead one to have an appetite for a meal in the evening when the parasympathicotonic state becomes dominant. On the other hand, the omission of a daytime meal on days of unusual shifts may result from loss of appetite connected with transfer of sleeping hours into daytime and accompanying disturbances of the circadian rhythm. This would be so especially if the day's caloric consumption remains at a low level, as is the case in most types of modern industrial work. Unlike the old two-meals-a-day habit, the reduction of meals resulting from shift work does not seem to guarantee the intake of sufficient nutrients. Shift workers seem to cut out a meal which would be affected by unusual daytime schedules and decrease of appetite. It should also be remembered that the other members of their families keep the three-meal habit and the shift workers themselves adhere to it when on day shifts, so that as a result their meal habits are greatly confused from one shift period to another. There is much evidence that a large number of shift workers suffer from digestive disorders. Thus, even within the three-meal habit, which is seen also among double-day shifters, the change of the time of meals and their intervals would raise significant nutritional problems. Adequate measures should be taken in order to prevent the diminution of meal frequency in shift rotation and the adverse effects of the irregularity of meal taking on the nutrition of shift workers. REFERENCES DRUMOND, J. C, and WILBRAHAM, A. (1971) The Englishman's Food. Jonathan Cape, London.

11 INFLUENCE OF SHIFT WORK ON MEAL TAKING 205 HOSOKAWA, J., SATO, S., MATSUMOTO, Y., HIROIKE, S., KATO, S., YAMAMOTO, N., MURAO, S., SAHEKI, A., MIURA, S., TAKESHIMA, K., SAITO, K., HIRAKAWA, S., MOTOORI, T., KIMURA, M., and INOUE, Y. (1971) Kojiruien (Glossary of old customs and manners), Yoshikawakobunkan, Tokyo. SATO, S. and TAKAGI, K. (1972) Studies on the effect of shift work on the meal-time (Part 3). J. Sci. Labour, 48: TAKAGI, K. and KOIZUMI, S. (1963) Studies on the effect of shift work on the meal-time (Part 1). J. Sci. Labour, 39: TAKAGI, K., KOIZUMI, S., and TAKAGI, N. (1967) Studies on the effect of shift work on the mealtime (Part 2). J. Sci. Labour, 43: