PURPOSE: To investigate the association between night shift work and bone mineral density (BMD) among 408 Buffalo police officers. METHODS: This cross-sectional study was conducted from 2004-2009. The percentage of work hours on night shift was derived from daily payroll work history records. BMD (gm/cm2) was measured by dual-energy x-ray absorptiometry (DXA). Mean BMD levels from five anatomical locations (total hip, femoral neck, AP spine, wrist, and total body) were compared across genderspecific tertiles of night shift work using ANOVA/ANCOVA; p-values were obtained using linear regression. RESULTS: Percentage of night shift work was significantly associated with BMD, but only among women (n = 108). In women, increasing tertiles of night shift work (1st tertile 0-0.51%, 2nd tertile 0.56-12.64%, 3rd Tertile 13.75-92.86%) was associated with generally decreasing mean levels of BMD of the total hip (1st tertile = 1.06 +/- 0.02, 2nd = 1.08 +/- 0.02, & 3rd = 0.96 +/- 0.02; p < 0.001), femoral neck (0.91 +/- 0.02, 0.94 +/- 0.02, 0.84 +/- 0.02; p = 0.012), AP spine (1.12 +/- 0.02, 1.17 +/- 0.02, 1.05 +/- 0.02; p = 0.035), and whole body (1.23 +/- 0.02, 1.24 +/- 0.02, 1.16 +/- 0.02; p = 0.009), but not wrist (p = 0.107), after adjusting for age, race/ethnicity, smoking status, and BMI. Among men, the associations between night shift work and BMD were not statistically significant. CONCLUSION: Night shift work, expressed as a percentage of total hours worked, was significantly and inversely associated with BMD among female officers. Future studies employing prospective designs and larger sample sizes should investigate the association between night shift work and BMD, including the role gender may play.
Cathy A. Tinney-Zara, MPH, MA, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Morgantown, WV, 26505