New research suggests that suffering anxiety and depression could increase the risk of dying from cancer.
Experts analysed data for 163,363 men and women who were free from cancer at the start of the study, of whom 4,353 went on to die from the disease.
The results showed that people categorised as the most distressed - such as suffering anxiety or depression - were a third more likely to die from a range of cancers than those who were least distressed.
The cancer types included bowel, prostate and pancreatic cancer.
Experts from University College London, the University of Edinburgh, and the University of Sydney published their findings in the British Medical Journal (BMJ).
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They examined 16 studies where psychological distress was measured using health questionnaires. People in the study were followed for around nine and a half years and factors that may influence the results, such as age, education and socio-economic situation, were taken into account.
"After statistical control for these factors, the results show that compared with people in the least distressed group, death rates in the most distressed group were consistently higher for cancer of the bowel, prostate, pancreas, and oesophagus and for leukaemia," said Dr David Batty from University College London.
The researchers said the study did not prove distress definitely caused increased death, and it may be that undiagnosed cancer lowers people's mood.
But further analysis of a sub-group of patients suggested a link between distress and cancer death remained despite this being taken into account.
"Our findings contribute to the evidence that poor mental health might have some predictive capacity for certain physical diseases but we are a long way off from knowing if these relationships are truly causal," Dr Batty said.
