A study at Ulm University and its Medical Centre has uncovered the molecular mechanisms by which psychological trauma and other massively stressful experiences slow down the healing of bone fractures. The research team, which included scientists from Canada and Japan, was able to demonstrate that certain immune cells respond to stress by producing an enzyme, which in turn promotes the release of stress hormones. These stress hormones act locally on the bone where they inhibit the conversion of cartilage cells into bone cells, thus slowing down bone growth and fracture healing.