Table 2. Single observational studies of the relationship between shift work and health.

Authors	Type of article	Number of studies/ participants	Summary findings
Cardiovascular Heart Disease
Vetter et al., 2016	Prospective cohort	N=189,158	Small but significant increase in risk among nurses with prolonged exposure (≥10 yr) to rotating night work (HR=1.15).
Breast cancer
Wegrzyn et al., 2017	Prospective cohort	N=78,516 & N=114,559	Increased risk associated with ≥ 20 yr exposure to night work, particularly among women exposed during young adulthood (Not significant in first study, women with ≥30 yr of shift work, follow-up primarily after retirement. HR=2.15 in second study, younger women with ≥20 yr of shift work; HR=1.4 in second study with updated exposure information).
Metabolic syndrome
Guo et al., 2015	Cross-sectional	N=25,382	Dose-response relationship with night work among women but not men (OR=1.10 for every 10 yr increase in shift work).
Type-2 diabetes
Silva-Costa et al., 2015	Cross-sectional	N=14,427	Increased risk associated with >20 yr exposure to night work in both sexes (RR=1.42 for women; 1.06 for men).
Hansen et al., 2016	Prospective cohort	N=19,873	Increased risk associated with night (OR=1.58) and evening shifts (OR=1.29), but not rotating shifts.
Reproduction
Gaskins et al., 2015	Prospective cohort	N=1,739	No association between shift work and fecundity.

‘Shift work’ defined as any pattern of irregular work hours that may or may not involve night work. ‘Night work’ defined as any pattern of shift work that includes night working. OR: odds ration; RR: relative risk; HR: hazard ratio.