Other than Daytime Working Is Associated with Lower Bone Mineral Density:
The Korea National Health and Nutrition Examination Survey 2009.
Calcif Tissue Int. 2013 Aug 21.
Kim BK, Choi YJ, Chung YS.
Department of Endocrinology and Metabolism, Ajou University School of Medicine, San 5 Wonchon-dong, Yeongtong-gu, Suwon, 443-721, South Korea.
Occupation affects bone mineral density (BMD); however, only few studies have been published. This study evaluated the effect of working time during a day on BMD. The cross-sectional study involved 18- to 50-year-old people who reported their working time and were measured for BMD using dual-energy X-ray absorptiometry in the Fourth Korea National Health and Nutrition Examination Survey 2009. The time period of work was divided into "daytime" and "other than daytime." The other-than-daytime group included evening time, nighttime, regular shift time, and irregular shift time.
Among 3,005 subjects,
- 2,378 were daytime workers and
- 627 were other-than-daytime workers.
The mean BMD of the total femur and lumbar spine were significantly lower in other-than-daytime workers compared to daytime workers (femur 0.948 vs. 0.966 g/cm2, respectively, p = 0.001; lumbar spine 0.976 vs. 0.988 g/cm2, respectively, p = 0.023).
The other-than-daytime group had lower levels of serum 25-hydroxyvitamin D than the daytime group (16.3 vs. 17.6 ng/mL, p < 0.001).
The proportion of osteopenia (T score < -1.0) was higher in the other-than-daytime than the daytime group (34.3 vs. 29.1 %, p = 0.014).
After adjustment for age, sex, socioeconomic status, lifestyle factors, daily intake of calcium, and vitamin D level, the relative risks of osteopenia of regular-shift and irregular-shift workers were significantly higher (1.65, 95 % CI 1.05-2.60; 1.78, 95 % CI 1.09-2.89) than those of daytime workers. These data suggest that other-than-daytime working, especially regular and irregular shift working, is associated with decreased BMD and increased risk for osteopenia in Korean adults.