Alwin van Drongelen a.vandrongelen@vumc.nl

1. The effects of shift work exposure on weight change: a systematic review of longitudinal studies Alwin van Drongelen a.vandrongelen@vumc.nl Cécile Boot, Suzanne Merkus, David Bruinvels, Hynek Hlobil, Allard van der Beek, Tjabe Smid

2. Introduction • Shift work and irregular working hours

3. Introduction • Shift work and irregular working hours • 20% of the European working population is involved in shift work • Netherlands: about 50% of the employees indicate they sometimes work during evening or night (NEA) • Only 24% of the workforce still has a “normal” nine to five dayjob (Costa 2003)

4. Introduction • Consequences..

5. Introduction • Health consequences of shift work • Gastrointestinal problems • Cardiovascular diseases • Unclear • Cancer • In 2007 the IARC classified 'shift work that involves circadian disruption' as a probable human carcinogen • Metabolic syndrome • Diabetes type 2 • Obesity

6. Introduction • Weight gain and obesity problem in current society • Shift work  weight gain ? • Problem: cross sectional studies • Objective of this systematic review • Study and summarise the available evidence for the relationship between longitudinal shift work exposure and weight change

7. Methods • Search strategy • Medline, Embase, Cochrane library, PsycINFO • Criteria • Full text available • Comparing shift workers with day workers • Longitudinal design • At least two measurements of a weight related outcome

8. Methods • Quality assessment • Modified version of checklists by Hayden et al.(2006) and Van der Windt et al.(2000) • Included • study objective and population • Exposure, confounder and outcome assessment • Data presentation and analysis • 14 items were scored +, - or ? • In case of “?” first authors were contacted to provide additional information • Quality was independently assessed by two reviewers, disagreements resolved in a consensus meeting • Low quality < 50% > high quality

9. Methods • Synthesizing the evidence • Levels of evidence synthesis (Hoogendoorn et al.(2000) and Sacket et al.(2000) Strong evidence: consistent findings found in multiple high-quality studies. Moderate evidence: consistent findings found in one high-quality study and at least one low quality cohort Weak evidence: consistent findings in one high-quality cohort or consistent findings in at least three low-quality cohorts. Inconclusive evidence: consistent findings in less than three low-quality cohorts. Inconsistent evidence: inconsistent findings irrespective of study quality. • Findings were considered consistent if at least 75% of the selected studies showed significant (p<0.05) results in the same direction.

10. Results

11. Results

12. Results • Study characteristics • 5 prospective, 2 retrospective studies • Follow up: 18 months – 14 years • Population: nurses or male factory personnel • # participants: 55 – 7254 • Outcome: weight in kg, BMI and waist circumference • Measured by physicians (5) or self reported (2) • Wide variety of measured confounders

13. Results • Exposure • Large differences between studies in • Shift work exposure • Shift systems • Day work exposure • No meta analysis possible due to heterogeinity between studies

14. Results • Outcome • 4 studies adjusted outcome for confounders (age, sex, baseline weight and physical activity) • 2 high quality studies found a significant difference in weight gain between groups • Inconsistent evidence • 6 studies presented non adjusted outcomes • 4 high quality studies found a significant difference in weight gain between groups • Inconsistent evidence

15. Explanation • Small amount of studies report weight changes • others did measure them, but did not report them • Levels of evidence lead to inconsistency because of the 75% rule. • Methodological quality • Possible selection bias • Healthy worker effect • Big differences in • (historic) exposure • Follow up period

16. Explanation • Worse health behaviour in shift workers • Less physical activity • More smoking • But different behaviour is not found in all studies • Food intake • Less healthy food available • During night • Irregular meal pattern • Meal frequency reduced • High energy snacking increases (Atkinson et al.2008)

17. Explanation • Effect of food intake during night • LDL cholesterol↑ • Insulin sensitivity↓ > insulin resistance↑ • Postprandial triaglycerol↑, triaglycerol clearance↓ • Leptin concentration↓ • Appetite↑ • Energy expenditure↓ • Might explain higher incidence of obesity and cardiovascular diseases found in shift workers. • Might increase the risk for weight gain and diabetes type2

18. Conclusion • No consistent evidence for an association between shift work exposure and weight gain • Future cohort studies should: • Report more weight related data • Refine exposure assessment • Use long follow up periods (>5 years) • Use newly employed shift workers • Explore the exact influence of food intake during night

19. What’s the time?

20. Results (2) • Subgroup analysis • Per type of work: inconsistent evidence • Per measurement type: inconsistent • Per geographical origin, Europe or Japan • Europe: moderate evidence for NO relation • Japan: strong evidence for an association between shift work exposure and weight gain in male factory personnel

21. Explanation (2) • No differences in weight gain epidemic between Japan and Europe.. • No differences in weight outcome variance • Different health behaviour? Studies adjusted for it.. • Different food intake? Not reported.. • Other suggestions? Any other questions??

22. ?