Null association between workplace social capital and body mass index. Results from a four-wave panel survey among employees in Japan (J-HOPE study)

Rationale: Research on the longitudinal association of workplace social capital and obesity is limited. Objective: We sought to investigate the prospective association of social capital in the workplace with body mass index (BMI) among employees in Japan. Methods: We used repeat panel surveys from 12 private companies in Japan. In the present study, four annual surveys waves were used, including 8811, 10,608, 9766, and 6249 participants, respectively. The first survey was conducted between October 2010 and December 2011 (response rate = 77.4%), and the following three surveys were conducted at approximately annual intervals. Questionnaires inquiring about workplace social capital, and other characteristics were administered at each survey. Height and weight were objectively measured in 11 companies, and self-reported in one company. Cross-sectional as well as fixed effects analysis of change in social capital and change in BMI were conducted. Analyses were stratified by age, sex, BMI at baseline, and companies. The analysis was conducted in 2015. Results: Over 3 years, approximately 32% of the participants changed their BMI by more than 1 unit, while workplace social capital changed for approximately 78% of the sample. We found no associations between change in workplace social capital and change in BMI. The null association was preserved across analyses stratified by sex, age, overweight/obesity status at baseline, and company. Conclusion: Workplace social capital is not associated with changes in employee BMI.