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. Sex-specific analyses showed that significantly lower hazard ratios were observed only in men in model 2, although point estimates were similar between sexes.

Table 1

Hazard ratios of incident diabetes according to commuter cycling status using a marginal structural model

Values based on commuter cycling statusP value
NoYes
N 27,712 3,140  
No. of cases 2,812 219  
Person-years 230,939 26,602  
Hazard ratios (95% CI)    
 All    
  Age and sex adjusted 1.00 (reference) 0.77 (0.68, 0.88) <0.001 
  Model 1* 1.00 (reference) 0.77 (0.68, 0.88) <0.001 
  Model 2 1.00 (reference) 0.75 (0.61, 0.93) 0.009 
  Model 3 1.00 (reference) 0.78 (0.63, 0.96) 0.020 
 Aged 30 to 64 years (n = 29,121)    
  Age and sex adjusted 1.00 (reference) 0.77 (0.68, 0.88) <0.001 
  Model 1* 1.00 (reference) 0.77 (0.67, 0.88) <0.001 
  Model 2 1.00 (reference) 0.75 (0.61, 0.94) 0.011 
  Model 3 1.00 (reference) 0.78 (0.63, 0.97) 0.026 
 Men (n = 26,899)    
  Age adjusted 1.00 (reference) 0.78 (0.67, 0.89) <0.001 
  Model 1* 1.00 (reference) 0.77 (0.67, 0.89) <0.001 
  Model 2 1.00 (reference) 0.78 (0.62, 0.98) 0.031 
  Model 3 1.00 (reference) 0.81 (0.65, 1.02) 0.067 
 Women (n = 4,779)    
  Age adjusted 1.00 (reference) 0.77 (0.54, 1.09) 0.14 
  Model 1* 1.00 (reference) 0.76 (0.53, 1.09) 0.14 
  Model 2 1.00 (reference) 0.80 (0.51, 1.24) 0.32 
  Model 3 1.00 (reference) 0.81 (0.52, 1.26) 0.35 
Values based on commuter cycling statusP value
NoYes
N 27,712 3,140  
No. of cases 2,812 219  
Person-years 230,939 26,602  
Hazard ratios (95% CI)    
 All    
  Age and sex adjusted 1.00 (reference) 0.77 (0.68, 0.88) <0.001 
  Model 1* 1.00 (reference) 0.77 (0.68, 0.88) <0.001 
  Model 2 1.00 (reference) 0.75 (0.61, 0.93) 0.009 
  Model 3 1.00 (reference) 0.78 (0.63, 0.96) 0.020 
 Aged 30 to 64 years (n = 29,121)    
  Age and sex adjusted 1.00 (reference) 0.77 (0.68, 0.88) <0.001 
  Model 1* 1.00 (reference) 0.77 (0.67, 0.88) <0.001 
  Model 2 1.00 (reference) 0.75 (0.61, 0.94) 0.011 
  Model 3 1.00 (reference) 0.78 (0.63, 0.97) 0.026 
 Men (n = 26,899)    
  Age adjusted 1.00 (reference) 0.78 (0.67, 0.89) <0.001 
  Model 1* 1.00 (reference) 0.77 (0.67, 0.89) <0.001 
  Model 2 1.00 (reference) 0.78 (0.62, 0.98) 0.031 
  Model 3 1.00 (reference) 0.81 (0.65, 1.02) 0.067 
 Women (n = 4,779)    
  Age adjusted 1.00 (reference) 0.77 (0.54, 1.09) 0.14 
  Model 1* 1.00 (reference) 0.76 (0.53, 1.09) 0.14 
  Model 2 1.00 (reference) 0.80 (0.51, 1.24) 0.32 
  Model 3 1.00 (reference) 0.81 (0.52, 1.26) 0.35 
*

Adjusted for age (continuous, years), sex, marital status (unmarried, divorced/separated, or married), job position (higher or lower), overtime hours worked (<45, 45–60, 60 to <80, 80 to <100, and 100 h or longer per month), shift work (yes or no), smoking (nonsmoker or current smoker consuming 1–10, 11–20, or ≥21 cigarettes per day), alcohol use (nondrinker or drinker consuming <1, 1 to <2, or ≥2 go of Japanese sake equivalent per day [1 go of Japanese sake contains approximately 23 g of ethanol]), sleep duration (<5, 5 to <6, 6 to <7, or ≥7 h per day), hypertension (yes or no, defined as systolic blood pressure ≥140 mmHg, diastolic blood pressure ≥90 mmHg, or currently taking medication for hypertension), and family history of diabetes (yes or no).

Further adjusted for leisure time physical activity (none, 1 to <60, 60 to <120, and ≥120 min per week), occupational physical activity (mostly sedentary, mostly standing, mostly walking, and mostly physically active), and time spent in walking to and from work (<20, 20–40, and 40 min or longer).

Further adjusted for BMI (kg/m2, continuous), which may be a mediator or confounder.

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 two or more commuting modes. Thus, we adjusted for time spent walking during commuting to minimize this influence. Third, unmeasured confounders (e.g., diet) may have affected the results. Fourth, the sample size was not large enough to study working women. Last, participants were workers in a specific industry. Caution should be exercised when generalizing the present findings.

In conclusion, we found that cycling as a primary mode of commuting to work is significantly associated with a lower diabetes risk. Our data emphasize the importance of cycling commuting in preventing diabetes in Asian populations.

Acknowledgments. The authors thank Toshiteru Ohkubo (Director of Industrial Health Foundation) for scientific advice on the Japan Epidemiology Collaboration on Occupational Health (J-ECOH) Study, Maki Konishi (National Center for Global Health and Medicine) for data management, and Rika Osawa (National Center for Global Health and Medicine) for administrative support.

Funding. The current study was supported in part by the Ministry of Health, Labor, and Welfare, Japan (JPMH20FA1006), Japan Society for the Promotion of Science Kakenhi (25293146, 16K21379, and 19K10671), funding from National Center for Global Health and Medicine (28-Shi-1206), and The Industrial Foundation.

These funding bodies had no role in the current study.

Duality of Interest. No potential conflicts of interest relevant to this article were reported.

Author Contributions. K.K. developed the study design, prepared the data set, and wrote the draft. S.S.S. suggested the performance of this study. T.Ho., S.Y., T.N., and T.Ha. contributed to collection of the data. H.N. helped to develop the study design and analyzed the data. S.S.S., H.N., and T.M. provided critical comments on the draft. T.M. critically advised as to study design. All authors interpreted the results and approved the final version of the manuscript. K.K. and T.M. are the guarantors of this work and, as such, had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

1.
Aune
D
,
Norat
T
,
Leitzmann
M
,
Tonstad
S
,
Vatten
LJ
.
Physical activity and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis
.
Eur J Epidemiol
2015
;
30
:
529
542
2.
Rasmussen
MG
,
Grøntved
A
,
Blond
K
, et al
.
Associations between recreational and commuter cycling, changes in cycling, and type 2 diabetes risk: a cohort study of Danish men and women
.
PLoS Med
2016
;
13
:
e1002076
3.
Hu
FB
,
Sigal
RJ
,
Rich-Edwards
JW
, et al
.
Walking compared with vigorous physical activity and risk of type 2 diabetes in women: a prospective study
.
JAMA
1999
;
282
:
1433
1439
4.
Villegas
R
,
Shu
XO
,
Li
H
, et al
.
Physical activity and the incidence of type 2 diabetes in the Shanghai women’s health study
.
Int J Epidemiol
2006
;
35
:
1553
1562
5.
Kuwahara
K
,
Yamamoto
S
,
Honda
T
, et al
.
Improving and maintaining healthy lifestyles are associated with a lower risk of diabetes: a large cohort study
.
J Diabetes Investig
2022
;
13
:
714
724
Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered. More information is available at https://www.diabetesjournals.org/journals/pages/license.