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.
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