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Rotating night shift work and adherence to unhealthy lifestyle in predicting risk of type 2 diabetes: results from two large US cohorts of female nurses

BMJ 2018; 363 doi: https://doi.org/10.1136/bmj.k4641 (Published 21 November 2018) Cite this as: BMJ 2018;363:k4641
  1. Zhilei Shan, research fellow1 2,
  2. Yanping Li, research scientist2,
  3. Geng Zong, research fellow2,
  4. Yanjun Guo, research fellow3 4,
  5. Jun Li, research fellow2 3,
  6. JoAnn E Manson, professor3 5,
  7. Frank B Hu, professor2 3 6,
  8. Walter C Willett, professor2 3 6,
  9. Eva S Schernhammer, professor3 6 7,
  10. Shilpa N Bhupathiraju, research scientist2 6
  1. 1Department of Nutrition and Food Hygiene, Hubei Key Laboratory of Food Nutrition and Safety, Ministry of Education Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China
  2. 2Department of Nutrition, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA
  3. 3Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, USA
  4. 4Department of Occupational and Environmental Health, Ministry of Education Key Lab of Environment and Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
  5. 5Division of Preventive Medicine, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA
  6. 6Channing Division of Network Medicine, Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA
  7. 7Department of Epidemiology, Center for Public Health, Medical University of Vienna, Austria
  1. Correspondence to: Z Shan zshan{at}hsph.harvard.edu
  • Accepted 27 October 2018

Abstract

Objectives To prospectively evaluate the joint association of duration of rotating night shift work and lifestyle factors with risk of type 2 diabetes risk, and to quantitatively decompose this joint association to rotating night shift work only, to lifestyle only, and to their interaction.

Design Prospective cohort study.

Setting Nurses’ Health Study (1988-2012) and Nurses’ Health Study II (1991-2013).

Participants 143 410 women without type 2 diabetes, cardiovascular disease, or cancer at baseline.

Exposures Rotating night shift work was defined as at least three night shifts per month in addition to day and evening shifts in that month. Unhealthy lifestyles included current smoking, physical activity levels below 30 minutes per day at moderate to vigorous intensity, diet in the bottom three fifths of the Alternate Healthy Eating Index score, and body mass index of 25 or above.

Main outcome measures Incident cases of type 2 diabetes were identified through self report and validated by a supplementary questionnaire.

Results During 22-24 years of follow-up, 10 915 cases of incident type 2 diabetes occurred. The multivariable adjusted hazard ratios for type 2 diabetes were 1.31 (95% confidence interval 1.19 to 1.44) per five year increment of duration of rotating night shift work and 2.30 (1.88 to 2.83) per unhealthy lifestyle factor (ever smoking, low diet quality, low physical activity, and overweight or obesity). For the joint association of per five year increment rotating night shift work and per unhealthy lifestyle factor with type 2 diabetes, the hazard ratio was 2.83 (2.15 to 3.73) with a significant additive interaction (P for interaction <0.001). The proportions of the joint association were 17.1% (14.0% to 20.8%) for rotating night shift work alone, 71.2% (66.9% to 75.8%) for unhealthy lifestyle alone, and 11.3% (7.3% to 17.3%) for their additive interaction.

Conclusions Among female nurses, both rotating night shift work and unhealthy lifestyle were associated with a higher risk of type 2 diabetes. The excess risk of rotating night shift work combined with unhealthy lifestyle was higher than the addition of risk associated with each individual factor. These findings suggest that most cases of type 2 diabetes could be prevented by adhering to a healthy lifestyle, and the benefits could be greater in rotating night shift workers.

Footnotes

  • Contributors: ZS, FBH, and SNB were involved in the study conception and design. ZS analyzed and interpreted the data. YL, GZ, and YG provided statistical expertise. ZS drafted the manuscript. All the authors participated in the interpretation of the results and critical revision of the manuscript. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted. ZS and SNB have full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis; they are the guarantors.

  • Funding: This study was supported by research grants UM1 CA186107, R01 HL034594, R01 HL088521, UM1 CA176726, UM1 CA167552, R01 OH009893, R01 HL35464, P30 DK46200, and R01 DK112940 from the National Institutes of Health (NIH). ZS is supported by the Young Scientists Fund of the National Natural Science Foundation of China (81703214) and the China Postdoctoral Science Foundation (2016M602314). SNB is supported by a career development grant from the NIH (K01 DK107804). The funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; or the decision to submit the manuscript for publication.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organization for the submitted work other than those detailed above; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: The Institutional Review Boards of Brigham and Women’s Hospital and the Harvard T. H. Chan School of Public Health approved this study. Return of the mailed questionnaire was considered to imply informed consent. Protocol number: 2009-P-002375.

  • Transparency declaration: The lead authors (the manuscript’s guarantors) affirm that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

  • Data sharing: The statistical code and technical processes are available from the corresponding author at zshan@hsph.harvard.edu.

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