The Relationship Between Shift Work and Obesity Among Canadian Nurses
Smith P, Fritschi L, Reid A, Mustard C
Shift Work and Obesity
Shift work is associated with many negative health effects, such as obesity. However, the mechanism that leads to the relationship between shift work and obesity and the direction of the relationship are unclear. Does shift work lead to increased body mass index (BMI) and, if so, why? Or are individuals with a higher BMI more likely to choose to work the night shift? Equally unclear is what can be done to mitigate this relationship. The purpose of this study was to examine the relative contribution of factors known to affect BMI, such as health behaviors and working conditions (employer-supported health clubs, healthy food options) in nurses working evening and night shifts. The second goal was to determine whether employer-supported facilities had an effect on BMI.
Methods. The researchers conducted a secondary analysis of data from a random, national, cross-sectional survey of Canadian nurses conducted in 2005. Height, weight, shift typically worked (days, evenings, nights, or rotating), whether the respondent had a say in hours or days they worked, and tenure in current job were all reported. A job questionnaire assessed job strain and effort-reward imbalance, including measures such as job control, psychological demands, and respect and support. Two health behaviors, smoking and alcohol use, were assessed. Survey participants were asked about facilities for physical activity and places to purchase healthy food. Finally, potential confounders such as age, marital status, children, restrictions to physical activity, self-reported episodes of major depression, type of nurse, and type of workplace were included.
More than 18,000 nurses completed the telephone interview. Researchers eliminated nurses who were not working in direct care facilities, those who were pregnant, those working multiple jobs, and individuals with incomplete responses, leaving a final sample of approximately 8600 female nurses.
Findings. BMI levels were higher in nurses working night or rotating-shift schedules compared with day-shift nurses, even after adjusting for all potential confounders. That difference in BMI, although statistically significant, was within 1 point across all shift schedules. The difference in BMI level for nurses working the night shift was not attenuated by differences in working conditions, the presence of employer-supported facilities, or health behaviors that are thought to be associated with weight gain. After adjusting for confounders, nurses working the night shift, on average, had BMI scores that were 0.67 points higher than those working the day shift; the BMI scores of nurses working rotating-shift schedules were 0.44 points higher. Higher levels of job strain were also associated with higher BMI levels, although the actual differences in BMI were less than 1 point. An interesting ancillary finding was that nurses working rotating shifts had higher job strain scores, increased imbalance in efforts and rewards, and were more likely to smoke.
This study is limited by the lack of direct measures of physical activity and diet and the fact that height and weight data were obtained only by self-report. However, the large sample size and the inclusion of multiple variables that may affect BMI are strengths, and the conclusions are worth noting. Nurses working off shifts have higher BMIs — and hospital efforts such as providing fitness facilities and options for healthy food do not attenuate that relationship. It is encouraging, however, that the difference, although achieving statistical significance because of this large sample size, is not likely to be significant in terms of health.
There probably isn’t a nurse out there who can’t identify with how difficult it is to work nights or a rotating-shift schedule and still fit in exercise, preparing and eating healthy foods, family obligations, and the myriad tasks that many women juggle. It is no surprise that the researchers also found that rotating shifts was particularly stressful and led to more job strain. My take on this study is that nurses working these schedules are to be congratulated on maintaining a BMI that is more or less in line with their day-shift colleagues’ despite the obstacles to doing so.