A recently published large Finnish longitudinal population study finds pre-existing depression to predict worse prognosis of cardiovascular disease (CVD) and cancer.

Previous studies have suggested that the symptoms of depression are negatively associated with the prognosis of cardiovascular diseases and cancer. However, because depression has usually not been measured before the diagnosis, these studies have been unable to rule out the possibility for reverse causality, that is, the higher risk of developing post-diagnosis depression among patients with a worse prognosis.

This new Finnish study, using linked administrative data, measured depression by registered antidepressant purchases before the first diagnosis of CVD or cancer among individuals with no history of these diseases, thus avoiding the possibility of reverse causality and selection bias. Pre-existing depression was associated with a 10%–35% excess mortality after the diagnosis of coronary heart disease, stroke and cancer. These results call for more attention in the healthcare system for CVD and cancer patients with a history of depression.