The association between shift work, body mass index and low back pain in a cohort of nurses and midwives.

Background Shift work is a defining occupational feature of nursing and midwifery professions. It has various adverse effects that could ultimately affect building and maintaining a healthy nursing and midwifery workforce. Firstly, shift work interrupts people‟s daily routines; therefore, it may lead to poorer lifestyle factors that increase one‟s risk of being overweight or obese. Secondly, shift work is reported to be one of the occupational risk factors for low back pain, which is a common problem among nurses. Aim This research aims to examine the association between shift work, body mass index(BMI) and low back pain (LBP) among nurses and midwives recruited from Australia, New Zealand and the United Kingdom. Methods To understand the impact of shift work on BMI, both cross-sectional and longitudinal cohort studies were undertaken using data from the Nurses and Midwives‟ e-cohort Study (NMes). The NMeS is a longitudinal population-based study recruiting nurses and midwives from Australia, New Zealand and the United Kingdom; and it is conducted completely electronically from recruitment to follow-up. There were 10, 120 total registrants, of whom, 7604 registrants completed survey 1 and 5280 registrants completed survey 2. The average follow-up period was two years. Two cross-sectional studies were carried out to explore the effects of shift work in general and specific shift types (rotating shift work and night-only shift work) on BMI. A longitudinal cohort study was undertaken to better understand the causal relationship between shift work and BMI. Similarly, a second longitudinal study was conducted to investigate the association between shift work and LBP, which also included an interaction analysis of the combining effects of shift work and overweight/obesity on LBP. Detailed statistical methods used for each study were discussed in each paper. Results The results from the two cross-sectional studies showed that almost 60% of the recruited nurses and midwives were overweight or obese. Shift workers were at higher risk of being overweight and obese compared to day workers (aRR: 1.15, 95% CI 1.03 - 1.28, p = 0.013; aRR: 1.14, 95% CI 1.02 - 1.30, p = 0.02, respectively). Regarding the specific shift types, rotating shift work was found to be associated with both overweight and obesity (aRR: 1.02, 95% CI 1.004 – 1.03 p = 0.007; aRR: 1.02,95% CI 1.004 – 1.04, p = 0.02, respectively); and night-only shift work was only found to be associated with obesity (aRR: 1.02, 95% CI 1.002 – 1.04, p = 0.031), but not associated with being overweight. The adjusted relative risk (1.02) was small, which may not reflect clinical significance although the results were statistically significance. Furthermore, shift work is consisted of many different kinds of schedules including rotating shift and night-only shift. Therefore, it was decided to further test the association between shift work in general (including any kind of shift schedules) and BMI using a longitudinal study design, which found a decrease in BMI among those participants who maintained day work and especially among those who changed from shift work at Survey One (S1) to day work at Survey Two (S2)(decrease in BMI of 3.02) during the two years‟ follow up; an increase in BMI among those participants who maintained shift work and those who changed from day work at S1 to shift work at S2 (p < 0.001). These studies demonstrate that shift work is significantly associated with overweight/obesity/increase in BMI; and overweight or obesity is reported to have an impact on LBP. Therefore, in the longitudinal study of examining the association between shift work and LBP, the impact of the interaction between shift work and overweight/obesity on LBP was also examined. The results showed that shift workers were at higher risks of developing LBP compared to day workers (aOR: 1.15, 95% CI 1.05 – 1.40, p = 0.03). The [shift schedule * BMI classification] interaction showed that shift workers who were overweight and obese were more likely to develop LBP than day workers (overweight: aOR: 1.23, p < 0.01; obesity: aOR: 1.34, p < 0.01). Conclusion Shift workers were at higher risk of being overweight or obese and developing LBP compared to day workers. Whilst shift work cannot be avoided in nurses and midwives, interventions targeting weight reduction and LBP prevention should be tailored to the specific work settings. If the adverse effects of shift work can be mitigated with strategic intervention, the potential workforce implications of these morbidities may be prevented