Weekly Working Hours and Serum Vitamin D3 Levels Among Korean Wage Workers: Evidence From KNHANES 2022–2023

Objective To examine whether weekly working hours are associated with serum vitamin D levels among Korean wage workers. Methods This cross-sectional study used data from 2,988 adults in the 2022–2023 Korea National Health and Nutrition Examination Survey. Serum 25(OH)D 2 and 25(OH)D 3 were measured by liquid chromatography–mass spectrometry. Associations with weekly working hours were analyzed using multivariable linear regression, adjusting for age, sex, education, and occupation. Results Each additional weekly working hour was associated with a 0.057 ng/mL decrease in 25(OH)D 3 levels, with no significant association for 25(OH)D 2 . The inverse association was stronger among white-collar, highly educated, and obese workers. Conclusions Long working hours are significantly linked to lower serum vitamin D 3 levels. These findings highlight working hours as a modifiable occupational determinant of vitamin D deficiency, particularly in indoor or white-collar settings.