The Burden of Occupational Disease and Injury in New Zealand: Technical Report
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4. Other Aspects of Workplace Hazards
4.1 SHIFT WORK
Summary Shift work is work that forces sleep to be displaced, with most research focused on night work and rotating shift systems. Shift work has been associated with a range of work-related disorders. The main one of these is sleep disturbance, from which other health problems can flow. Other health effects of shift work, for which there are varying degrees of evidence, include peptic ulceration, ischaemic heart disease, female reproductive disorders, obesity, diabetes mellitus, hypertension, disorders of the immune system and a range of psychological and relationship disorders. Several other disorders are hampered in terms of treatment or symptom control, but not necessarily caused by shift work. Only one New Zealand study provides evidence of a link between shift work and ill-health. This recent study provides evidence of a relationship between night work and sleep disorders. This study also estimated that 15.8% of Māori worked nights compared to 10.5% of non-Māori, and that women had a lower prevalence of night work than men (9.7% versus 15.2%). A paper from the Department of Labour estimated that 6.8% of current workers performed night work. Many New Zealand occupations involve working shift work.
Introduction
Shift work is work that forces sleep to be displaced.
Conditions
Shift work has been associated with a range of work-related disorders. The main one of these is sleep disturbance, from which other health problems can flow. Shift work sleep disorder is defined as symptoms and signs of insomnia or excessive sleepiness that occur as transient phenomena in relation to work schedules. Additional problems can be reduced alertness and problems with personal relationships away from work. An associated condition is irregular sleep-wake patterns, characterised by temporally disorganised and variable episodes of sleeping and waking behaviour[501]. Sleep disorders are also associated with a work week often longer than 48 hours, exposure to vibrations and various psychosocial factors[502].
Other health effects of shift work, for which there are varying degrees of evidence, include peptic ulceration, ischaemic heart disease, female reproductive disorders, obesity, diabetes mellitus, hypertension, disorders of the immune system and a range of psychological and relationship disorders. Several other disorders are hampered in terms of treatment or symptom control, but not necessarily caused by shift work. These include diabetes mellitus, epilepsy, and disorders of the thyroid, respiratory system and kidney. Another emerging issue is the possible exacerbating effect that shift work may have on the toxic effect of certain hazardous substances, due to the possible influence on circadian metabolic functions[503, 504, 505].
New Zealand Studies of risk
Only one New Zealand study provides evidence of a link between shift work and ill-health. This recent study provides evidence of a relationship between night work and sleep disorders. A questionnaire was mailed out to a stratified random sample of Māori and non-Māori persons aged 20 to 59 years. The response rate was 73%. Compared to employed persons not working nights, participating in night work increased the risk of reporting "often/always" having difficulty falling asleep (OR = 1.36, 95% CI 1.03 – 1.81), having a current sleep problem (OR = 1.64, 95% CI 1.24 – 2.18), and having a chronic sleep problem (OR = 1.61, 95% CI 1.20 – 2.17)[506].
New Zealand exposures
The study of night work in New Zealand described above provides an estimate of night work in New Zealand. The study estimated that 15.8% of Māori worked nights (between 0000 and 0500), compared to 10.5% of non-Māori persons. Women had a lower prevalence of night work than men (9.7% versus 15.2%)[506].
A paper from the Department of Labour provides another estimate of the prevalence of shift work in New Zealand, based on the New Zealand Time Use Survey 1998/9. Evening work was defined as work undertaken between 1900 and 2400. Night work was defined as work undertaken between 0000 and 0500. Evening work was undertaken by 24.5% of current workers and night work by 6.8%. Night work was slightly more common for men compared to women (7.9% versus 5.2%) and in Pacific Islanders and Māori compared to Pakeha (14.5%, 10.7% and 6.2% respectively). Night work was also more common in plant and machine operators (16.8%), elementary occupations (14.7%), and service and sales workers (8.4%)[507].
Another study investigated the role of work, rest and recovery in the occurrence of injuries in forest workers, for whom work raised major physical and psychological demands. Seven per cent of 361 subjects reported working night work as part of their normal pattern of work[508].
Many New Zealand occupations involve working shift work.
