People can die simply because they've given up, life has beaten them and they feel defeat is inescapable, according to new research.

The study, by Dr John Leach, a senior research fellow at the University of Portsmouth, is the first to describe the clinical markers for 'give-up-itis', a term used to describe what is known medically as psychogenic death.

The five stages of give-up-itis are:

1. Social withdrawal
2. Apathy
3. Aboulia
4. Psychic akinesia
5. Psychogenic death

In concentration camps, people who reached this stage were often known to be near death by fellow prisoners when they took out a hidden cigarette and began smoking it. Cigarettes were highly valuable in the camps and could be traded for important things such as food.

Dr Leach said: "When a prisoner took out a cigarette and lit it, their campmates knew the person had truly given up, had lost faith in their ability to carry on and would soon be dead."