Selection into shift work is influenced by educational attainment and body mass index: a Mendelian randomization study in the UK Biobank

Iyas Daghlas; Rebecca C Richmond; Jacqueline M Lane; Hassan S Dashti; Hanna M Ollila; Eva S Schernhammer; George Davey Smith; Martin K Rutter; Richa Saxena; Céline Vetter

doi:10.1093/ije/dyab031

Selection into shift work is influenced by educational attainment and body mass index: a Mendelian randomization study in the UK Biobank

Int J Epidemiol. 2021 Aug 30;50(4):1229-1240. doi: 10.1093/ije/dyab031.

Authors

Iyas Daghlas^{1

2}, Rebecca C Richmond³, Jacqueline M Lane^{1

2

4}, Hassan S Dashti^{1

2

4}, Hanna M Ollila^{1

2

5}, Eva S Schernhammer^{6

7}, George Davey Smith³, Martin K Rutter^{8

9}, Richa Saxena^{1

2

4}, Céline Vetter^{1

10}

Affiliations

¹ Broad Institute of MIT and Harvard, Cambridge, MA, USA.
² Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA, USA.
³ MRC Integrative Epidemiology Unit, Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK.
⁴ Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
⁵ Institute for Molecular Medicine Finland (FIMM), HiLIFE, University of Helsinki, Helsinki, Finland.
⁶ Channing Division of Network Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
⁷ Department of Epidemiology, Center for Public Health, Medical University of Vienna, Vienna, Austria.
⁸ Division of Endocrinology, Diabetes and Gastroenterology, Faculty of Biology, Medicine and Health, School of Medical Sciences, University of Manchester, Manchester, UK.
⁹ Diabetes, Endocrinology and Metabolism Centre, Manchester University NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, UK.
¹⁰ Department of Integrative Physiology, University of Colorado at Boulder, Boulder, CO, USA.

Abstract

Background: Shift work is associated with increased cardiometabolic disease risk. This observation may be partly explained by cardiometabolic risk factors having a role in the selection of individuals into or out of shift work. We performed Mendelian randomization (MR) analyses in the UK Biobank (UKB) to test this hypothesis.

Methods: We used genetic risk scores (GRS) to proxy nine cardiometabolic risk factors and diseases (including educational attainment, body mass index (BMI), smoking, and alcohol consumption), and tested associations of each GRS with self-reported frequency of current shift work among employed UKB participants of European ancestry (n = 190 573). We used summary-level MR sensitivity analyses to assess robustness of the identified effects, and we tested whether effects were mediated through sleep timing preference.

Results: Genetically instrumented liability to lower educational attainment (odds ratio (OR) per 3.6 fewer years in educational attainment = 2.40, 95% confidence interval (CI) = 2.22-2.59, P = 4.84 × 10-20) and higher body mass index (OR per 4.7 kg/m2 higher BMI = 1.30, 95% CI = 1.14-1.47, P = 5.85 × 10-5) increased odds of reporting participation in frequent shift work. Results were unchanged in sensitivity analyses allowing for different assumptions regarding horizontal pleiotropy. No selection effects were evident for the remaining exposures, nor for any exposures on selection out of shift work. Sleep timing preference did not mediate the effects of BMI and educational attainment on selection into shift work.

Conclusions: Liability to lower educational attainment and higher BMI may influence selection into shift work. This phenomenon may bias epidemiological studies of shift work that are performed in the UKB.

Keywords: Body mass index; Mendelian randomization; UK Biobank; cardiometabolic disease; confounding; educational attainment; obesity; shift work.

Publication types

Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

MeSH terms

Biological Specimen Banks
Body Mass Index
Genome-Wide Association Study
Humans
Mendelian Randomization Analysis*
Polymorphism, Single Nucleotide
Risk Factors
Shift Work Schedule*
United Kingdom / epidemiology

Abstract

Publication types

MeSH terms

Grants and funding