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  3. Contribution of modifiable risk factors to social inequalities in type 2 diabetes: prospective Whitehall II cohort study
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Research

Contribution of modifiable risk factors to social inequalities in type 2 diabetes: prospective Whitehall II cohort study

BMJ 2012; 345 doi: https://doi.org/10.1136/bmj.e5452 (Published 21 August 2012) Cite this as: BMJ 2012;345:e5452
  1. Silvia Stringhini, research fellow1,
  2. Adam G Tabak, clinical research associate23,
  3. Tasnime N Akbaraly, senior research fellow245,
  4. Séverine Sabia, research associate2,
  5. Martin J Shipley, senior lecturer2,
  6. Michael G Marmot, professor of epidemiology and director2,
  7. Eric J Brunner, reader2,
  8. G David Batty, Wellcome Trust fellow26,
  9. Pascal Bovet, professor of epidemiology and public health1,
  10. Mika Kivimäki, professor of social epidemiology2
  1. 1Institute of Social and Preventive Medicine, Lausanne University Hospital, 1010 Lausanne, Switzerland
  2. 2University College London, Department of Epidemiology and Public Health, London, UK
  3. 3Semmelweis University, Faculty of Medicine, 1st Department of Medicine, Budapest, Hungary
  4. 4Inserm U1061, Montpellier, France
  5. 5Université Montpellier I, Montpellier, France
  6. 6MRC Centre for Cognitive Ageing and Cognitive Epidemiology, University of Edinburgh, Edinburgh, UK
  1. Correspondence to: S Stringhini silvia.stringhini{at}chuv.ch
  • Accepted 25 July 2012

Abstract

Objective To assess the contribution of modifiable risk factors to social inequalities in the incidence of type 2 diabetes when these factors are measured at study baseline or repeatedly over follow-up and when long term exposure is accounted for.

Design Prospective cohort study with risk factors (health behaviours (smoking, alcohol consumption, diet, and physical activity), body mass index, and biological risk markers (systolic blood pressure, triglycerides and high density lipoprotein cholesterol)) measured four times and diabetes status assessed seven times between 1991-93 and 2007-09.

Setting Civil service departments in London (Whitehall II study).

Participants 7237 adults without diabetes (mean age 49.4 years; 2196 women).

Main outcome measures Incidence of type 2 diabetes and contribution of risk factors to its association with socioeconomic status.

Results Over a mean follow-up of 14.2 years, 818 incident cases of diabetes were identified. Participants in the lowest occupational category had a 1.86-fold (hazard ratio 1.86, 95% confidence interval 1.48 to 2.32) greater risk of developing diabetes relative to those in the highest occupational category. Health behaviours and body mass index explained 33% (−1% to 78%) of this socioeconomic differential when risk factors were assessed at study baseline (attenuation of hazard ratio from 1.86 to 1.51), 36% (22% to 66%) when they were assessed repeatedly over the follow-up (attenuated hazard ratio 1.48), and 45% (28% to 75%) when long term exposure over the follow-up was accounted for (attenuated hazard ratio 1.41). With additional adjustment for biological risk markers, a total of 53% (29% to 88%) of the socioeconomic differential was explained (attenuated hazard ratio 1.35, 1.05 to 1.72).

Conclusions Modifiable risk factors such as health behaviours and obesity, when measured repeatedly over time, explain almost half of the social inequalities in incidence of type 2 diabetes. This is more than was seen in previous studies based on single measurement of risk factors.

Footnotes

  • We thank all of the participating civil service departments and their welfare, personnel, and establishment officers; the British Occupational Health and Safety Agency; the British Council of Civil Service Unions; all participating civil servants in the Whitehall II study; and all members of the Whitehall II Study Team. The Whitehall II Study Team comprises research scientists, statisticians, study coordinators, nurses, data managers, administrative assistants, and data entry staff, who make the study possible.

  • Contributors: SStringhini analysed the data and wrote the first and successive drafts of the paper. MK conceived the study. MK, AT, MS, and SSabia contributed to data analysis. All authors contributed to the interpretation of results and to the writing of the paper, critically revised each version of the manuscript, and approved the final version of the paper. S Stringhini is the guarantor.

  • Funding: SStringhini is supported by a postdoctoral fellowship awarded by the Swiss School of Public Health. MK is supported by the UK Medical Research Council (MRC), the US National Institutes of Health (NIH) (R01HL036310; R01AG034454), the EU New OSH ERA Research Programme, and an Economic and Social Research Council (ESRC) professorship. DB is a Wellcome Trust fellow. TA is supported by the National Heart, Lung, and Blood Institute (R01HL036310). SSabia is supported by a grant from the National Institute of Aging, NIH (R01AG034454). MS is supported by the British Heart Foundation. The Whitehall II study has been supported by grants from the MRC; the British Heart Foundation; the British Health and Safety Executive; the British Department of Health; the National Heart, Lung, and Blood Institute (R01HL036310); and the National Institute on Aging, NIH. The University of Edinburgh Centre for Cognitive Ageing and Cognitive Epidemiology is funded as part of the joint UK research council call for lifelong health and wellbeing. The funding organisations or sponsors had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; or preparation, review, or approval of the manuscript.

  • 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 organisation for the submitted work; no financial relationships with any organisations 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: This study was approved by the University College London ethics committee, and all participants provided written consent.

  • Data sharing: Whitehall II data are available to the scientific community. Please refer to the Whitehall II data sharing policy at www.ucl.ac.uk/whitehallII/data-sharing.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: http://creativecommons.org/licenses/by-nc/2.0/ and http://creativecommons.org/licenses/by-nc/2.0/legalcode.

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