Alcohol and Circadian Disruption Minimally Impact Bone Properties in Two Cohorts of Male Mice While Between‐Cohort Differences Predominate: Association With Season of Birth?

Many lifestyle factors affect bone. Sleep deprivation increases risk for fractures and alcohol consumption can lead to alterations in the skeleton. How combined exposure to these two risk factors affects bone is unclear. Thus, we sought to determine the effects of circadian rhythm disruption and chronic alcohol intake on bone structure and mechanical properties in mice. A total of 120 male C57BL/6J mice were used in two cohorts of 60 mice each because of limited availability of light‐tight housing cabinets. One cohort was born in winter and the other in summer. Mice were randomly assigned to circadian disruption (weekly shifting of the light/dark cycle) and control (no shifting) groups beginning at 8 to 12 weeks of age for 12 weeks at which time mice were administered an alcohol‐containing or control diet for an additional 10 weeks. Bone structure and mechanical properties of the femur were assessed by micro‐computed tomography and three‐point bending, respectively. The initial data analysis revealed a likely cohort effect. Thus, we used a three‐way analysis of variance to assess the effects of circadian rhythm disruption, alcohol intake, and cohort. Circadian rhythm disruption alone had minimal effects on bone structure and mechanical properties. Alcohol intake reduced body mass and had minimal effects on cortical bone regardless of circadian disruption. Alcohol intake resulted in higher trabecular bone volume, but these beneficial effects were blunted when circadian rhythm was disrupted. Cohort significantly affected body size, many cortical bone structure outcomes, some trabecular bone structure outcomes, and tissue‐level material properties. Thus, cohort had the predominant effect on bone structure and mechanical properties in this study, with chronic alcohol intake and environmental circadian disruption having less consistent effects. The data indicate that season of birth may affect skeletal phenotypes and that studies requiring multiple cohorts should determine if a cohort effect exists. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.