What is shiftwork?

Work that is scheduled outside "normal" daylight hours (i.e. 9 am to 5 pm) is called "Shiftwork". Shiftwork schedules can vary from one workplace to another. Workers may rotate through shifts or remain on a single shift (i.e. permanent nights).

Where does shiftwork occur?

Shiftwork allows for continuous services and production, 24 hours per day. Examples of such around-the-clock work include health care, customs and immigration, electrical utilities, and transportation – to name a few. Many manufacturing and seasonal workplaces also work 24 hours a day to maximize efficiency and productivity.

Work hours

The modern expectation of a regular work schedule is a 40-hr workweek, 8-hrs a day, Monday-through-Friday. With the introduction of shiftwork, a 5-day workweek may change to a 4 or 3-day workweek depending on the length of a single shift.

Studies have examined the differences between various workweek schedules. When comparing a 5-day/8-hr work schedule to a 4-day/10-hr work schedule, most studies found that workers were more tired at the end of a 10-hr shift. Studies also found workers to be more fatigued following a 12-hr shift when compared to an 8-hr shift.

Night shifts can also be tiring. Mental and physical effects of night work have been shown to affect a worker's concentration, alertness, motivation, and memory. This can slow a worker's reaction time and increase the risk of accident. Unfortunately, night work cannot be avoided in some occupations.

Why does shiftwork affect us?

Circadian Rhythms
Our body's "biological" clocks help maintain complex internal functions throughout a 24-hr day. A number of physiological functions show distinct rhythmic changes (called Circadian Rhythms) in the course of a 24-hour period. For example, your heart rate and body temperature change throughout a 24-hour period and are typically lowest around 4:00 am and peak in mid-afternoon. The graph below shows how your body temperature may rise and fall in a 24-hour period.

The body's various Circadian Rhythms are "reset" every 24 hours by environmental cues, such as light and darkness. For example, body temperature increases with daylight and decreases at night (see graph).

The human body is meant to be active during daytime hours, while during nighttime hours it is meant to sleep which allows it to recover and replace energy. Working at night and sleeping during the day is opposite to the body's "biological" clocks and what the body naturally wants to do. This may make sleeping difficult; it may also mean that the body cannot recover as quickly from physical and mental exertions/demands.

Mental & Physical Performance

Circadian rhythms have been found to be associated with changes in mental and physical performance. Circadian rhythms may partly explain why job performance can vary over a 24-hour period, with a low point occurring very late at night or very early in the morning.

Some basic human physiological functions are depressed during the night, which may suggest that people are not well suited for night work.

Performance on the night shift can be affected by:

• The type of shift schedule
• The nature of the task(s)
• The performance demands of the task
• Adjustments to tasks and shifts
• Individual differences

Shiftwork & women's health

One study found the risk of breast cancer to be 60 percent higher in women who worked the night shift (beginning work after 7:00 pm and finishing before 9:00 am) compared to those who did not. The improper production of the hormone melatonin is though to be associated with this increased breast cancer risk. Melatonin is a hormone primarily produced during nighttime sleep and it has an affect of regulating estrogen and also serves as an antioxidant.

Irregular menstrual cycles and menstrual pains were reported from women in a number of industries who worked night shifts.

Higher risk of miscarriage, lower rates of pregnancies and deliveries, spontaneous abortion, delayed fetal development, increased risk of pre-term delivery and low birth weight have also been observed in some studies.

Tips for workers who must work shifts

Dietary and Eating Patterns

• Afternoon workers should have their meal in the middle of the day instead of the middle of their work shift
• Night workers should eat lightly throughout the shift and have a moderate breakfast
• Relax during meals and allow time for digestion
• Drink lots of water
• Cut back on highly salted foods
• Reduce foods high in fat
• Maintain regular eating patterns with well balanced meals (avoid junk food & limit fat intake)
• Eat the usual balance of vegetables, fruit, lean meat, poultry, fish, dairy products, grains, and bread
• Avoid excessive use of antacids, tranquilizers and sleeping pills
• Minimize the intake of caffeine and alcohol
• Avoid fast food and vending machines

Sleep

• Make sure that family and friends are aware of and considerate of the worker's sleep hours and needs
• Ensure you have a comfortable, quiet place to sleep during the day
• Air conditioning, telephone answering machine, foam ear plugs and good blinds are examples of devices that may improve the worker's sleep
• Make time for quiet relaxation before bed to facilitate better sleep (reading, breathing exercises, muscle relaxation techniques, etc.)
• Sleep on a set schedule to help establish a routine and to make sleep during the day easier
• Avoid strenuous exercise before sleeping because your body's metabolism will remain elevated for several hours and this makes sleeping difficult
• If failing to fall asleep after one hour, read a book or listen to quiet music
• If sleep still does not come, reschedule sleeping hours for later in the day

Social Activities

• Schedule at least one daily meal with the family; this helps to keep communication channels open and promotes a good eating habit
• Socialize with other shift workers and their families; this helps to minimize the disruption that shift work can have on your social life
• Keep in touch with spouse and children daily
• Establish good communication skills
• Set time aside for just you and your spouse
• Carefully plan family activities; family ties are a precious commodity (plan days off in advance if possible)
• Pay close attention to physical fitness; a regular exercise program helps the body adjust to the negative effects of shiftwork and it can also help improve the quality and quantity of sleep
• Practice stress reduction
• Use a calendar to schedule events
• Try to prioritize tasks and tackle one at a time

References

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Davis S., Mirick D.K. and Stevens R.G. (2001). Night shift work: Light at night, and the risk of breast cancer. Journal of the National Cancer Institute. 93: 1557-1562.

Eastman Kodak Company. (1986). Ergonomic Design for People at Work: Volume 2. Van Nostrand Reinhold, New York.

Fraser, T.M. (1989). The Worker at Work. Taylor & Francis, New York.

Grandjean, E. (1988). Fitting the Task to the Man; 4th Edition. Taylor & Francis, New York.

Ontario Natural Resources Safety Association. (1996). Living With Shiftwork. 690 McKeown Ave. PO Box 2050. North Bay, Ont. P1B 9P1.

Salvendy, G. (1997). Handbook of Human Factors and Ergonomics; 2nd Edition. John Wiley & Sons, Inc., New York

Schernhammer E.S. et al (2001). Rotating night shifts and risk of breast cancer in women participating in the nurses' health study. Journal of the National Cancer Institute. 93(20):1563-1568.

Schernhammer E.S. and Hankinson S.E. (2003). Light at night: A novel risk factor for cancer in shift workers? Clinics in Occupational and Environmental Medicine. 3:263-278.

Schernhammer E.S. et al. (2003). Night-shift work and risk of colorectal cancer in the nurses' health study. Journal of the National Cancer Institute. 95(11): 25-28.

Scott, A.J., and Ladou, J. (1990). Shiftwork: Effects on Sleep and Health With Recommendations for Medical Surveillance and Screening. Occupational Medicine. 5(2): 273-299.

Stevens R.G. and Davis S. (1996). The Melatonin Hypothesis: Electric Power and Breast Cancer. Environmental Health Perspectives. 104(supp 1).

Stones, I. (1987). Rotational Shiftwork: A summary of the Adverse Effects and Improvement Strategies. CCOHS: Hamilton.

Sudbury and District Health Unit. (1995). Shiftwork Like Clockwork. SDHU: Sudbury.

Taylor, E., Briner, R.B., and Folkard, S. (1997). Models of Shiftwork: An Examination of the Influence of Stress on Shiftwork Theory. Human Factors. 39(1): 67-82.

Wedderburn, A.A.I. (1981). How important are the social effects of shiftwork? In L.C. Johnson, D.I. Tepas, W.P. Colquhoun, and M.J. Colligan, Eds., Biological Rhythm, Sleep and Shift Work. New York: Spectrum.

Wedderburn, A.A.I. (1991). Guidelines of Shiftworkers. Bulletin of European Shiftwork Topics, No. 3. Dublin: European Foundation for the Improvement of Living and Working Conditions.

Yamada et al. (2001). Excessive fatigue and weight gain among cleanroom workers after changing from an 8-hour to a 12-hour shift. Scandinavian Journal of Work, Environment, & Health. 27 (5): 318-26.

Mitchell R.J. and Williamson A.M. (2000). Evaluation of an 8 hour versus a 12 hour shift roster on employees at a power station. Applied Ergonomics. 31(1): 83-93.

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Revised 2005