Vitamin D status is often low in ill patients but it remains poorly understood if this is a cause or consequence of the illness. To explore this issue further, colleagues in VitDAL teamed up with the orthopaedic service at HfSA to measure inflammatory biomarkers and vitamin D metabolites in dogs undergoing elective treatment of a ruptured cruciate ligament before, immediately after surgery and several weeks post surgery. The collaborative project showed that total vitamin D concentrations transiently decreased immediately following surgery but returned to pre-operative values several weeks post surgery. Interestingly, free 25(OH)D concentrations were less dramatically effected by surgery and did not decline significantly in the immediate post operative period. Ionised calcium and parathyroid hormone concentrations did not change significantly during the study period. As expected, CRP concentrations dramatically increased immediately post surgery and then declined to pre-surgery baseline values several weeks post surgery. Collectively, our data showed that elective surgery can cause a transient decline in total 25(OH)D concentrations and highlight the challenges of ascertaining vitamin D status when measuring total 25(OH)D concentrations in ill patients. The paper can be accessed via this link