BACKGROUND: Downsizing can often have a detrimental effect on employee health and increase sickness absence. Earlier research has theoretically argued that such negative consequences are due to taxing alterations in the work environment, but research efforts to empirically test this argument remain limited. METHODS: In this study, we investigate whether the environment for control, role clarity, and commitment in different work units can explain the relationship between unit-level downsizing and sickness absence. We combined register- and self-reported data from 19,173 employees in a large Norwegian health trust in the period 2011-2015 and conducted a longitudinal fixed effects analysis. RESULTS: Unit-level downsizing was found to be significantly related to increased short-term sickness absence, reduced organizational commitment, and reduced control. Reduced commitment explained a small part of the increase in short-term sickness absence after unit-level downsizing. There was no mediating effect of either control or role clarity. CONCLUSION: The study contributes to a better understanding of the underlying mechanisms that help explain why downsizing leads to adverse health consequences and sickness absence by highlighting the complexity of this relationship and introducing organizational commitment as a relevant mediator.