Shift work and body composition: a systematic review and meta-analysis

Introduction: There has been a dramatic increase in the practice of shift work throughout the world. It is known to associate with several adverse health outcomes including increased adiposity. The present study aims to systematically evaluate the literature to find the associations between exposure to shift work and body composition.Evidence acquisition: Data were obtained using a stepwise search process using keywords in the following online medical databases; PubMed®, Web of Science® and Scopus® for studies published before 31st March 2020. Studies which compared the outcome related to the body composition of shift workers and regular day workers were included. A meta-analysis was performed on body fat percentage (BF%).Evidence synthesis: Initial database searching indicated 2311 potentially eligible articles, of which 7 studies satisfying the inclusion criteria were selected. The number of participants ranged between 17 to 7318, and the age range of the subjects was between 20-65 years. The studies reported diverse shift schedules including rotating shifts, night, evening shifts, alternate shifts, and regular shifts. Four out of seven studies revealed a higher BF% in shift workers when compared to the non-shift group. The pooled mean difference for BF % between shift workers and regular workers was 1.77% (95% CI: 0.18, 3.35; p=0.03; I2=52%, p >0.12).Conclusions: The meta-analysis of the review showed a significant increase in BF% of shift workers when compared to the non-shift group. However, individual studies showed considerable heterogeneity. Therefore in order to further clarify the underlying mechanisms, more and better quality studies on this field are necessary.