But it has been known for a long time that people with no serious illness other than depression are more likely to die than those who are otherwise similar, but mentally healthy.

ECONOMIST: The power of negative thinking

However, at this stage there is no firm proof that depression actually causes cancer patients to die earlier than they otherwise would.

BBC: Depression 'cuts cancer survival'

We know that the majority of people who die by suicide have an underlying and often undiagnosed mental illness such as depression or bipolar disorder.

CNN: Why more Americans are dying of suicide