Dose-response relationship between working hours and obesity risk
方法 研究资料来源于中国健康与营养调查（China Health and Nutrition Survey，CHNS），选取具有完整人口统计学、每周工作时长和体质量指数等调查数据的18~65岁人群作为研究对象。以每周工作35~48 h为对照，通过多因素COX回归分析每周工作时长不超过34 h、49~55 h以及至少56 h对肥胖发生风险的影响，利用限制性立方样条模型分析工作时长与肥胖之间的剂量反应关系。
结果 共纳入9 319个调查样本，其中男性5 005人，女性4 314人。年龄（39.2±13.0）岁，平均随访8.66年。截至最后一次随访调查，共有640人发生肥胖，肥胖发生率为6.9%。多因素COX回归结果显示，与对照组相比，每周工作时长不超过34 h和每周工作时长至少56 h者的肥胖发生风险较高，其风险比（HR）及其95%可信区间（95% CI）分别为1.33（1.07~1.65）和1.36（1.13~1.65），尚未发现每周工作49~55 h与肥胖之间的关联。从不同性别来看，每周工作时长至少56 h与男性的肥胖发生风险有关联，其HR及其95% CI为1.40（1.09~1.79）；每周工作时长不超过34 h则与女性的肥胖发生风险有关联，其HR及其95% CI为1.42（1.04~1.94）。从不同工作类型来看，每周工作时长至少56 h与体力劳动者的肥胖发生风险相关，其HR及其95% CI为1.34（1.07~1.67），尚未发现每周工作时长与非体力劳动者肥胖发生风险之间的关联。工作时长和肥胖呈"U"型剂量反应关系（总趋势P < 0.05，非线性P < 0.05），当每周工作时长小于50 h，肥胖发生风险随着工作时长的增加而降低，超过50 h后肥胖发生风险随着工作时长的增加而上升。
Background With the development of social economy, the influence of working time on obesity has received increasing attention. However, there is a lack of studies on the dose-response relationship between working hours and obesity.
Objective This study evaluates the association between different working hours and obesity and the dose-response relationship between them.
Methods The data were obtained from the China Health and Nutrition Survey (CHNS), and subjects aged 18-65 years with completed demographics, weekly working hours, and body mass index were included. Using working 35-48h per week as reference, multivariate COX regressions were conducted to assess the associations between weekly working hours (≤ 34 h, 49-55 h, and ≥ 56 h) and the risk of obesity. Restricted cubic spline models were used to analyze the dose-response relationship between working hours and obesity.
Results A total of 9 319 individuals were included, including 5 005 males and 4 314 females. Their age was (39.2±13.0) years, and the mean follow-up time was 8.66 years. By the last follow-up, a total of 640 participants developed obesity, and the incidence rate of obesity was 6.9%. The results of multivariate COX regression showed that the hazard ratio (HR) and 95% confidence interval (95% CI) of obesity was 1.33 (1.07-1.65) and 1.36 (1.13-1.65) respectively for the groups working ≤ 34 h and ≥ 56 h per week compared with the reference group, and the association between working 49-55 h per week and obesity was not found. Regarding sexes, working ≥ 56h per week was associated with the risk of obesity of males (HR=1.40, 95%CI:1.09-1.79), and working ≤ 34h per week was associated with the risk of obesity of females (HR=1.42, 95% CI:1.04-1.94). Regarding types of work, working ≥ 56h per week was associated with the risk of obesity in manual workers (HR=1.34, 95% CI:1.07-1.67), and the association in nonmanual workers was not observed. There was a U-shaped dose-response relationship between working hours and obesity (Ptrend < 0.05, non-linear P < 0.05). The risk of obesity decreased with increasing working hours when working < 50h per week, and elevated with increasing working hours when working >50h per week.
Conclusion Both short and long working hours may be associated with the risk of obesity. There is a U-shaped dose-response relationship between working hours and obesity. Long working hours have more significant effects on obesity in male workers and manual workers.