Analysis of Multi-center Longitudinal Data Using Multilevel Model for Assessing the Relationship between Work Schedule and Body Mass Index Among Staff of Mobarakeh Steel and Polyacryl Companies

Shift work could threaten health in the long term. The present research aimed to assess the association between shift work and body mass index (BMI) using the multilevel (hierarchical) model during a particular period of time.
The data of this longitudinal study were collected from a sample of Esfahan’s Mobarakeh steel and Polyacryl companies personnel during 2008 to 2011. Shift work schedule included day work and rotational shift work. The multilevel regression model was utilized for analysing the data and assessing the effect of shift work on BMI by controlling confounding variables including marital status, work expectation, age, company, and educational level.
In this study, of 1368 workers, 42.3% (n=578) and 57.7% (n=790) were day workers and rotating shift workers, respectively. The mean (±SD) age of the day workers and rotating shift workers was 33.07 (±8.66) years and 33.31 (±8.70) years, respectively. After adjusting for confounding variables in a two-level hierarchical model, the association between shift work and BMI was not statistically significant (P=0.837). About 90% of total variation was related to personnel.
According to the results of the present study, no statistically significant relationship was found between shift work schedule and BMI. Thus, other similar studies with a longer follow up period (more than four years) and controlling more confounder factors are necessary to evaluate the relationship between shift work and BMI more accurately.