Cross-sectional study of the association between long working hours and pre-diabetes: 2010-2017 Korea national health and nutrition examination survey

OBJECTIVE: Long working hours have been shown to raise the risk of various health outcomes. However, epidemiological evidence has shown inconsistent result in relation to type 2 diabetes mellitus (T2DM) and the association between long working hours and pre-diabetes among non-diabetic adults remains largely unexplored. We thus aimed to investigate whether long working hours were linked with pre-diabetes as determined by glycated haemoglobin (HbA1c) level. DESIGN: Cross-sectional survey. PARTICIPANTS: This study included 6324 men and 4001 women without diabetes from the 2010 to 2017 Korean National Health and Nutrition Examination Survey. PRIMARY OUTCOME MEASURES: The study outcome of interest was pre-diabetes, defined as HbA1c values 5.7% to 6.4% RESULTS: Logistic regression was performed to obtain the ORs for pre-diabetes according to categories of work hour (40 hours/week, 41 to 52 hours/week, >52 hours/week), after adjusting for relevant covariates. Of the 10 325 eligible participants, 2261 (34.4%) men and 1317 (31.0%) women had pre-diabetes. No statistically significant relationship was found for women. In men, extended working hours (>52 hours per week) was associated with an increased likelihood of pre-diabetes, after adjustment for age, educational attainment, monthly household income, lifestyle related factors, perceived stress, family history of diabetes, hypertension, hypercholesterolaemia and other covariates (adjusted OR=1.22; 95% CI 1.03 to 1.46). In the subgroup analysis by occupational categories, the association was only apparent among men in blue-collar worker groups. CONCLUSION: Extended working hours were significantly related to pre-diabetes in men, with no statistically significant association observed for women. Further subgroup analysis by occupational categories revealed that the increased odds of pre-diabetes associated with long working hours was only apparent among male workers of blue-collar occupations and shift workers.