A study published by The BMJ today suggests that higher levels of psychological distress (anxiety and depression) may be associated with an increased risk of death from certain cancers.
The findings are observational, so no firm conclusions about cause and effect can be drawn. However, the authors say their findings add to the growing evidence that psychological distress could have some predictive capacity for certain physical conditions.
There is some evidence that psychological distress (anxiety and depression) is related to increased rates of cardiovascular disease, but links with different types of cancer are either unclear or untested.
So a team of researchers from University College London, University of Edinburgh, and University of Sydney set out to examine if psychological distress is a potential predictor of site specific cancer mortality.
They analysed data from 16 studies (13 from England and three from Scotland), which started between 1994 and 2008. In total, 163,363 men and women aged 16 or over and free from cancer at the start of the study, were included.
Psychological distress scores were measured using the general health questionnaire and participants were monitored for an average of nine and a half years. During this time, there were 4,353 deaths from cancer.
Several factors that could have influenced the results were taken into account, including age, sex, education, socioeconomic status, BMI, smoking and alcohol intake.
Dr David Batty from University College London, the lead author, said: "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."
The authors point out that this association may also be affected by reverse causality, where undiagnosed (early) cancer might have had an underlying impact on mood.
In a bid to correct for this, they carried out a further analysis excluding study participants who died in the first five years of follow-up, but this made no difference to the findings - the links between distress and cancer remained.
Dr Batty said: "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."
Research: Psychological distress in relation to site specific cancer mortality: pooling of unpublished data from prospective cohort studies http://www.