Leisure-Time, Occupational, and Commuting Physical Activity and Risk of Type 2 Diabetes in Japanese Workers: A Cohort Study

Toru Honda; Keisuke Kuwahara; Tohru Nakagawa; Shuichiro Yamamoto; Takeshi Hayashi; Tetsuya Mizoue

Disclosures

BMC Public Health. 2015;15(1004) 

In This Article

Methods

Study Procedure

The present study was conducted as a sub-study of the Japan Epidemiology Collaboration on Occupational Health (J-ECOH) Study, an ongoing, large-scale study among workers in several companies.[24,25] The J-ECOH Study was announced in each company by using posters, and workers were given an opportunity to refuse the use of their data for research, according to the Japanese Ethical Guidelines for Epidemiological Research. The study protocol was approved by the Ethics Committee of the National Center for Global Health and Medicine, Japan.

Of the participating companies in the J-ECOH Study, the present analysis included data from one company (an electrical machinery and apparatus manufacturing) where detail information on physical activity has been collected as a part of periodic health check-ups since 2006.

Participants

In Japan, workers are obliged to undergo health checkup at least once a year under the Industrial Safety and Health Act. A total of 40,948 workers (34,700 men and 6,248 women) aged 30 to 64 years received health check-ups between April 2006 and March 2007 (baseline period). Of these individuals, 11,434 workers were excluded due to lack of information on the variables needed to diagnose diabetes (n = 7,655), having a history of diabetes (defined using HbA 1c, fasting or random plasma glucose, a medical history of diabetes, or currently taking medication for diabetes) (n = 3,376). Workers were also excluded if they having a history of cancer, cardiovascular disease, or stroke (n = 766). We excluded an additional 2,964 workers due to lack of information on exposure or covariates (n = 2,515) as well as engagement in only unspecified leisure activity (named "Other") (n = 487). Some of the participants met one or more of the exclusion criteria. Finally, we excluded 1,303 participants who did not attend any subsequent health check-up or who did not have data on HbA 1c or blood glucose in a subsequent health examination, which left 26,628 workers (23,207 men and 3,421 women) aged 30 to 64 years for inclusion in our study.

General Health Examination

Body height was measured to the nearest 0.1 cm and body weight to the nearest 0.1 kg. BMI was calculated as weight in kilograms divided by squared height in meters. The systolic and diastolic blood pressures were assessed using an oscillometric method with an automated sphygmomanometer (BP-203RV III; Colin, Tokyo, Japan) in a sitting position after a 5 min rest. The history of disease, work-related factors, and health-related lifestyle factors, including physical activity, alcohol consumption, and sleep duration, were collected using a standard questionnaire. Biochemical measurements included plasma glucose and HbA 1c . The blood glucose levels were determined using the glucose electrode technique. HbA 1c was measured with an HPLC method. HbA 1c was assessed according to a standard method used by the Japan Diabetes Society. We converted the HbA 1c measurements to the National Glycohemoglobin Standardization Program equivalent value (%) using the formula: HbA1c(%) = 1:02 × HbA1c (Japan Diabetes Society)(%) + 0:25 %.[26]

Physical Activity Questionnaire

Participants were asked if they were regularly engaging in any physical activity during their leisure time. If they engaged in physical activity, they were also asked to choose up to 3 activities among a list of 20 activities and describe the frequency (times per month) as well as the duration (minutes) for each activity. If participants were engaged in activities that were not listed in the questionnaire, they were instructed to choose an activity of similar intensity from the list.

Of the 20 regular exercise or sports activities, one activity, "Other," was not used for further analysis. The value of metabolic equivalents (METs) for each activity was assigned according to a compendium of physical activities.[27] If the MET value of an activity was not listed in the compendium, we assigned a MET value from a similar activity. Of the 19 activities, 13 (walking not for work or commuting, walking fast not for work or commuting, swimming, golf practice, golf, baseball, softball, bike cycling, table tennis, pang pong, badminton, muscle strength training, and radio gymnastics) were classified as moderate activities (3 to 6 METs) and 6 (light jogging [approximately 6 min/km], jogging, soccer, tennis, aerobics, and jump rope) were classified as vigorous activities (>6 METs), and these activities were used to calculate the weekly MET-hours of leisure-time exercise by multiplying the METs, duration, and frequency of the activity. These activities covered the most of common activities in Japan.[28] Following the physical activity guidelines, the participants were categorized into four groups according to the dose of leisure-time exercise per week: inactive (0 MET-hours), low (0.1 to <7.5 MET-hours), medium (7.5 to <15.0 MET-hours), and high (≥15.0 MET-hours).[7,8] These cutoff points were used in previous studies.[18,29] Individuals in each category of leisure-time exercise dose were further divided into the following three groups: individuals who engaged in moderate-intensity exercise alone, vigorous-intensity exercise alone, and both moderate- and vigorous-intensity exercise.

Occupational physical activity was assessed by a single question with four response options (mostly sedentary, mostly standing, walking often, or fairly active). Duration of walking for commuting to and from work (min per day) was self-reported.

Assessment of Other Variables

The information on smoking, alcohol consumption, sleep duration, shift work, and a family history of diabetes was collected using a standard questionnaire during the health check-ups. Smoking status (never, past, or current) and, if the individual was a smoker, the number of cigarettes smoked per day were also ascertained during the health check-ups. The total amount of alcohol consumption for each individual was calculated using the data on the frequency (number of days per week) and amount of consumption of common alcoholic beverages (Japanese sake, beer, whiskey, shochu, chuhai, and wine) per day, which was indicated by an equivalent amount of one unit (go) of Japanese sake. One go of Japanese sake contains approximately 23 g of ethanol.

Assessment of Type 2 Diabetes

Diabetes was identified using data from the annual health check-ups for a maximum of 6 years after the baseline examination. Diabetes was defined as HbA 1c ≥6.5 % (48 mmol/mol), fasting plasma glucose ≥126 mg/dl (7.0 mmol/l), random plasma glucose ≥200 mg/dl (11.1 mmol/l), or currently under medical treatment for diabetes. Individuals without diabetes at baseline who met any of the above conditions in the subsequent check-ups were considered to have an incident case of type 2 diabetes.

Statistical Analysis

The descriptive results of study population are expressed as the mean for continuous variables and percentages for categorical variables. The differences across the dose of leisure-time physical activity were tested by using linear regression for continuous variables and logistic regression for categorical variables.

Person-time was calculated from the date of the baseline examination to the date of diagnosis with diabetes at a subsequent examination or to the date of the last examination, whichever came first. The HR and the 95 % CI for the incidence of diabetes associated with leisure-time exercise, occupational physical activity, and walking to and from work were estimated by using Cox proportional hazards models. First, we adjusted for age (years, continuous) and sex (model 1). Then, model 2 was further adjusted for shift work (yes or no), smoking status (non-smoker, current smoker consuming 1 to 10, 11–20, or ≥21 cigarettes per day), alcohol consumption (non-drinker, drinker consuming <1, 1 to <2, ≥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 a systolic blood pressure ≥140 mmHg, a diastolic blood pressure ≥90 mmHg, or currently taking medication for hypertension), a family history of diabetes (yes or no), and other two types of physical activity. That is, occupational physical activity (mostly sedentary, mostly standing, walking often, or fairly active) and commuting physical activity (<20, 20 to <40, or ≥40 min of walking for commuting to and from work) were adjusted for leisure-time exercise, leisure-time exercise and commuting physical activity were adjusted for occupational physical activity, and leisure-time exercise and occupational physical activity were adjusted for commuting physical activity. In model 3, BMI (kg/m 2, continuous) was adjusted for.

Trends in the association between physical activity and diabetes risk were assessed by determining the median value in each category of leisure-time physical activity. The lowest category of each activity was considered as a reference. For combined associations of the dose and intensity of leisure-time physical activity, participants who did not engage in leisure-time exercise were references for our analyses. We repeated the analysis for dose of moderate-intensity exercise and vigorous-intensity exercise, respectively. In addition, we conducted analysis for each specific type of leisure-time exercise and risk of diabetes; participants were classified as those who engaged in specific activity or not. We tested the proportional-hazards assumption with the Schoenfeld residuals. We found no significant deviations for all of the covariates, except for smoking and occupational physical activity. As a sensitivity analysis, we excluded participants with a follow-up period of less than three years. Two-sided P values <0.05 were considered to be statistically significant. All analyses were performed with Stata version 13.1 (Stata Corp, College Station, Texas).

processing....