Low bone mineral density in rotating-shift workers

Shift workers have been reported to have an increased bone resorption. However, no existing evidence indicates lower bone mineral density (BMD) in this group. The objective of this study was to test the hypothesis that a rotating-shift work schedule is associated with low BMD and osteoporosis. We evaluated 70 postmenopausal nurses from the Naval Hospital in Concepcion, Chile. The participants were categorized according to the type of work schedule: 39 had a rotating shift and 31 were daytime workers. Medical history, a health examination, a questionnaire on health-related behaviors and biochemical determinations, and BMD examination were obtained for all participants. When comparing the 2 groups, the rotating-shift workers had lower BMD in the lumbar spine (L1-L4: 0.957 ± 0.15 vs 1.104 ± 0.13; p<0.05) and lower bone density in both femoral neck bones (right: 0.936 ± 0.17 vs 1.06 ± 0.12; p<0.05 and left: 0.956 ± 0.19 vs 1.05 ± 0.12; p<0.05). Additionally, the T-scores for 10 (25.6%) of the rotating-shift workers indicated osteoporosis at lumbar spine (T-score>-2.5). No evidence of osteoporosis was found for daytime workers. When comparing the 2 groups, the rotating-shift workers had a higher prevalence of osteopenia (T-score=-1.0 to -2.5) than the daytime workers: 46.2% vs 35.5%, respectively. We found significant evidence that rotating-shift workers have lower BMD in the trabecular and cortical bones, thus suggesting that this type of work may be a risk factor for osteoporosis. Because this is the first time that this osteoporosis risk factor has been reported, the association needs to be replicated and confirmed in other settings.