Shiftwork
Full Profile
(Group 2A)
General Information
Shift work can be defined as the organization of working time by different teams in succession to cover more than the usual 8-hour work day, up to a 24 hour period.[1] Some people work shift work on rotation while others perform regularly scheduled day, evening or night shifts.[1] Shift work at night has been found to be the most disruptive to internal circadian rhythms.[2]
Circadian rhythms generate the sleep-wake cycle in humans,[4] acting as an internal biological ‘clock’.[1] Endogenous circadian rhythms are synchronized with environmental factors, particularly the 24-hour solar light-dark cycle.[14,15] Shiftwork outside of regular day time hours results in a mismatch between the body’s circadian rhythms and the solar light-dark cycle.[14] Circadian disruption is characterized by melatonin suppression, de-synchronization of rhythmic body processes (i.e. sleep patterns and food digestion), and de-regulation of genes involved in cancer pathways.[1,2]
IARC has classified shift work with circadian disruption as Group 2A, probably carcinogenic to humans, based on sufficient evidence in animals and limited evidence in humans.[3] Most studies investigating disruption of circadian rhythms in rodents showed a significant increase in tumour incidence following exposure to constant light, dim light at night, or simulated chronic jet lag.[2] Epidemiological studies have observed an increased risk of breast cancer in long-term night shift workers when compared to people not working at night.[2] In particular, two cohort studies of nurses[5,6] and one of flight attendants[7] found moderate increases in the risk of breast cancer. These findings are somewhat limited by factors such as potential confounding and inconsistent definitions of shift work.[2]
In addition to carcinogenic outcomes, shift work has been associated with changes in mental and physical performance at work, fatigue, stress, disruption to family and social life, depression and anxiety.[1,8,9] Digestive disorders such as indigestion, heartburn, nausea and loss of appetite and cardiovascular disorders such as hypertension have been observed in shift workers.[10] Shift work has also be linked to reproductive health problems in women and aggravation of previous health conditions such as asthma, diabetes and epilepsy.[9]
Shift work has been ranked by CAREX Canada as Group A (immediate high priority) for occupational settings. Prioritization was based on new evidence for carcinogenicity, the prevalence of exposure in Canada, and the feasibility of assessing exposure.
Regulations and Guidelines
No occupational exposure limits for shift work in Canada or any other international bodies in the US were located. In Europe, EU Council Directives ensure that member states take measures concerning night shift length, average working times (daily and weekly), and rest periods (daily and weekly ).[3] The International Labour Organization (ILO) has issued recommendations around night work frequency, shift length, and rest periods.[3] Both of the above pay special attention to pregnant and young workers.
Occupational Exposures
In North America and Europe, approximately 15-20% of the working population participates in night shift work.[3]
Shift work takes place in industries requiring continuous services or production, including health care, customs & immigration, electrical utilities, industrial manufacturing, mining, transport, communication, seasonal work placements, and the leisure & hospitality sectors.[1,2]
Shift Work in Canada
Statistics Canada conducts the General Social Survey (GSS) and Survey of Labour and Income Dynamics (SLID), both of which include questions regarding shift work.[11,12]
The definition of shift work on the GSS includes regular evening schedules; regular night schedules; rotating shifts (those that change periodically from days to evenings or to nights); split shifts (constituting two or more distinct periods each day); on call or casual (no prearranged schedule, such as substitute teachers); and irregular schedule (changeable, but usually arranged a week or more in advance, such as pilots); and other, non-day schedules.
In 2005, the GSS found that approximately 4.1 million (28% of employed) Canadians worked in schedules outside of regular day shifts.[11] Of these workers, 82% worked full time (>30 hrs/week). Due to the nature of certain industries, large proportions of their work forces participate in shift work.[11] These industries are listed in the following table:
Proportions of Workers Engaged in Shift Work, by Industry[11]
| Industry | Percent of workers engaged in shift work |
|---|---|
| Protective Services | 66% |
| Health | 45% |
| Sales and Service | 40% |
| Primary Industry | 42% |
| Business, finance, administrative |
12% |
| Natural and applied Science | <10% |
Type of Shift Work by Gender (among full-time shift workers)[11]
| Type | Men | Women |
|---|---|---|
| Rotating | 34% | 41% |
| Irregular | 35% | 25% |
| Evening | 10% | 14% |
| Night | 8% | 8% |
| Other | 13% | 12% |
Shift Work* by Industry and Sex (2005)[12]
| Industry | Men | Women |
|---|---|---|
| Manufacturing | 374,000 | 83,000 |
| Trade | 175,000 | 196,000 |
| Health Care & Social Assistance |
62,000 | 230,000 |
| Accomodation & Food Service |
110,000 | 137,000 |
| Public Administration | 109,000 | 27,000 |
Shift Work Among Canadian Nurses
Shift work is commonplace in Canadian nursing practice. In a recent survey (2005/2006), 54% of nurses reported that they usually worked regular nights, evenings, or mixed shifts.[13]
Temporal Trends of Shift Work in Canada
The number of full-time shift workers in Canada increased from 2.3 million in 1992 to 3.4 million in 2005.[11] The most common forms of shift work in 2005 were rotating and irregular schedules, with 1.2 and 1.1 million full-time workers, respectively. Another Statistics Canada survey has shown a similar trend.[12]
Sources
- Stevens RG, et al. Considerations of circadian impact for defining ‘shift work’ in cancer studies: IARC Working Group Report. Occup Envion Med 2011;68:154-162
- Straif K, et al. Carcinogenicity of Shift Work, Painting and Firefighting Lancet Oncology 2007;8(12):1065-66
- IARC (2010) Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 98. ‘Painting, Firefighting, and Shiftwork’
- Dijk DJ, et al. Functional Genomics of Sleep and Circadian Rhythm. Invited Review: Integration of human sleep-wake regulation and circadian rhythmicity. Journal of Applied Physiology, 2002;92:852-862
- Schernhammer ES, Laden F, et al. Rotating night shifts and risk of breast cancer in women participating in the nurses' health study. J Natl. Cancer Inst 2001;93(20):1563-8
- Schernhammer ES, Kroenke CH, Laden F, Hankinson SE. Night work and risk of breast cancer. Epidemiology 2006; 17:108–11
- Megdal SP, Kroenke CH, Laden F, Pukkala E, Schernhammer ES. Night work and breast cancer risk: a systematic review and meta-analysis. Eur J Cancer 2005; 41: 2023–32
- Saskatchewan Labour Occupational Health and Safety Division (1998) Managing Shiftwork.
- Shields, M. (2002) Shift work and health, Statistics Canada catalogue number 82-003 (PDF)
- CCOHS (1998) Rotation Shift Work
- Williams, C. (2008) Work-Life Balance of Shift Workers (Statistics Canada publication) (PDF)
- Statistics Canada (2011) Survey of Labour and Income Dynamics (SLID) Home Page
- Health Canada and Statistics Canada (2007) Findings from the 2005 National Survey of the Work and Health of Nurses (Free to order, or see the online summary.)
- Costa G, Haus E, Stevens R. Shift work and cancer – considerations on rationale, mechanisms, and epidemiology. Scand J Work Environ Health 2010;66(2):163-179
- Roenneberg T et al. ‘Epidemiology of the human circadian clock’. Sleep Medicine Reviews 2007;11:429-438
Other Resources
- Health Canada (2001) Work Life Conflict in Canada in the New Millennium (PDF)
- Brun, Jean-Pierre (2006) Assessing the Costs of Work Stress (PDF)
- Higgins C, Duxbury L, Lyons S. (2007) Reducing Work-Life Conflict: What Works? What Doesn’t? (Health Canada report)
- NIOSH (2004) Overtime and Extended Work Shifts: Recent Findings on Illness, Injuries, and health Behaviors (PDF)
- Borugain, M. (2005) Shift Work, Light-at-night, and Melatonin: Characterising a New Cancer-related Occupational Exposure (Work Safe BC Research Report) (PDF)