1. Social Environment and Weight Gain Anne Kouvonen 1, Roberto De Vogli 2, Mai Stafford 2, Thomas Cox 1 and Mika Kivimäki 2 1) Institute of Work, Health and Organisations, University of Nottingham; anne.kouvonen@nottingham.ac.uk 2) Department of Epidemiology and Public Health, Medical School, UCL INTRODUCTION Obesity research has mainly focused on biological, individual and behavioural factors. However, evidence is emerging that social environmental factors such as negative social relationships, may also be important. We are not aware of prior studies examining the association between negative aspects of close relationships and weight gain. OBJECTIVES The aim of this interdisciplinary quantitative study is to assess one aspect of social environment, negative aspects of close relationships, as a risk factor for weight gain. METHODS The study is a secondary analysis of the Whitehall II Study. The Whitehall II Study is an on-going prospective occupational cohort study, the target population of which was all non-industrial civil servants aged 35–55 years who worked in the London offices of 20 civil service departments at baseline (1985–8) (N=10,308; response rate 73%). Negative aspects of close relationships was assessed with the Close Persons Questionnaire at phases 1 (1985-8) and 2 (1989). Body mass index (BMI) and waist circumference (WC) were measured in clinical examination at phases 3 (1991-4) and 5 (1997-9). Covariates included socio- demographic characteristics, health behaviours and common mental disorder. Logistic regression analysis was used to estimate the association between negative aspects of close relationships and weight gain. Acknowledgements The Whitehall II study has been supported by grants from the Medical Research Council; British Heart Foundation; Health and Safety Executive; Department of Health; National Heart Lung and Blood Institute (HL36310), US, NIH: National Institute on Aging (AG13196), US, NIH; Agency for Health Care Policy Research (HS06516); and the John D and Catherine T MacArthur Foundation Research Networks on Successful Midlife Development and Socio-economic Status and Health. Anne Kouvonen was supported by a grant from the Economic and Social Research Council (ESRC) (RES-000-22-3489). We thank all participating civil service departments and their welfare personnel, and establishment officers; the Occupational Health and Safety Agency; the Council of Civil Service Unions; all participating civil servants in the Whitehall II study; 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. RESULTS Figure 1 summarises the results from the logistic regression analyses on the associations between negative aspects of close relationships and ≥10% increase in BMI and WC. Repeated exposure to negative aspects of close relationships was associated with weight gain. SUMMARY OF CONCLUSIONS Prolonged exposure to negative interactions in close relationships may increase the likelihood of weight gain in middle-aged men and women. The present study adds to the evidence that the development of obesity is related to the social environment in which people live. Figure 1. Association between negative aspects of close relationships and ≥10% weight gain: Odds ratios and their 95% confidence intervals from fully adjusted logistic regression models