LAUSR

Promoting physical activity is essential for preventing diabetes (1). Recently, cycling to work has gained much attention as a feasible way to increase one’s daily physical activity level. Further, cycling to work provides environmental benefits by helping to decrease automobile emissions, which could have adverse environmental and health effects. However, the impact of cycling to work on diabetes prevention has been scarcely investigated (2), even when not specific to commuting (3,4). Moreover, the evidence is sparse in Asian populations. Thus, we assessed prospectively the association between commuter cycling and risk of type 2 diabetes among adults in Japan as a substudy of the Japan Epidemiology Collaboration on Occupational Health Study. We performed a cohort study with updated exposure yearly from fiscal year 2006 (baseline) to 2017 and capturing diabetes onset until 2017 using annual health checkup data. Details of the present cohort, including measurements of diabetes, lifestyle factors, and other covariates, were described previously (5). Overall, 50,877 workers (41,534 men) aged 20–80 years received health checkups at baseline. Of these, we excluded 16,005 workers due to a lack of data on the variables needed to diagnose diabetes (n = 12,694) or due to their having diabetes at baseline (n = 3,311). We then excluded 630 workers who had a history of cancer (n = 322), cardiovascular disease (n = 234), or stroke (n = 74) at baseline. Lastly, we excluded 2,564 workers for whom we did not have any data on commuting mode throughout the observation period (2006– 2017) or on diabetes status after the baseline, leaving 31,678 participants (mean age 44.0 years [SD 9.8]) for the main analysis. Participants reported primary mode of commuting at the annual health checkup using four response options (cycling, walking, train or bus, and car or motorbike); we classified them into two groups, cycling commuting or not, in each year. Diabetes diagnosis was defined as hemoglobin A1c $6.5% ($48 mmol/mol), fasting plasma glucose $126 mg/dL ($7.0 mmol/L), nonfasting plasma glucose $200 mg/dL ($11.1 mmol/L), or treatment for diabetes using annual health checkup data. We calculated hazard ratios of diabetes according to updated cycling commuting data using marginal structural Cox regression. We performed multiple imputation using chained equations to account for missing data on explanatory variables with 200 data sets for main and sensitivity analyses using R version 4.2.0. As shown in Table 1, the present data showed that, compared with noncycling commuters, diabetes risk was significantly lower among cycling commuters. When we adjusted for demographic, occupational, and lifestyle factors (model 1), hazard ratio for diabetes was 0.77 (95% CI 0.68–0.88) for cycling commuters compared with noncycling commuters. Additional adjustment for other domains of physical activity (model 2) and BMI (model 3) did not materially attenuate the results, although BMI levels after baseline were overall lower among cycling commuters (data not shown). Results were materially unchanged when participant age was restricted. Sexspecific analyses showed that significantly lower hazard ratios were observed only in men in model 2, although point estimates were similar between sexes. Our findings of a significantly lower risk of diabetes associated with cycling to work in Japanese men and women agree with findings from Danish men and women showing an inverse association of cycling commuting with diabetes risk (2). Our data seem to be in line with data of working women in China, showing that cycling in daily life was associated with 8% reduction in diabetes risk, although the reduction was not statistically significant (4). In their U.S. study, Hu et al. (3) simply reported that they observed nonsignificant results and did not show point estimates for diabetes risk. Thus, it is difficult to compare that study to ours. The present data, together with results from Danish (2) and Chinese (4) studies, suggest that cycling to work is beneficial in preventing diabetes for working adults. The current study has several limitations. First, we do not have detailed data on cycling commuting. Second, we evaluated the primary mode of commuting. Some participants may have engaged in