Another prospective study focussed on night shift health care workers and reported that working night shifts was associated with a greatly increased risk of metabolic syndrome (HR = 5.10, 95% CI 2.15–12.11) [48]. Lin et al. [49] found a significantly increased risk of developing metabolic syndrome in female persistent rotating shift workers compared to persistent day workers (OR = 3.5, 95% CI 1.3–9.0). In a similar study, Lin et al. [50] found an increased risk of developing metabolic syndrome in male persistent rotating shift workers, but only among those with elevated serum alanine aminotransferase at baseline (OR = 2.7, 95% CI 1.4–5.3), compared to non-persistent rotatingshift workers without elevated serum alanine aminotransferase. In contrast, a study of police officers did not find that those who mainlyworked midnight shifts had a higher risk of metabolic syndrome than those who mainly worked day shifts [51]. Because the day shifts started in the early morning (4:00 am) at the research site, this study may not be directly comparable with studies in which the reference group was dayshift workers with a more typical daytime work schedule.