People who are frequently depressed or anxious may run a higher risk of dying from certain types of cancer, researchers said on Thursday.
Medical records of more than 160,000 adults in England and Wales showed that those describing themselves as psychologically distressed were more likely to succumb to cancer, especially of the colon, prostate and pancreas.
Leukaemia and cancer of the oesophagus, or food pipe, were also more elevated among this group, they wrote in the BMJ medical journal.
The researchers were cautious in their conclusions, pointing out that a statistical link does not necessarily signify a cause-and-effect relationship between mood and cancer.
But the findings add to growing evidence that mental and physical health do not function on separate planes, and that one can influence the other, they said.
Earlier research, for example, showed that chronic depression and anxiety may help trigger heart disease and stroke.
But attempts to discern similar links between states of mind and cancer have yielded mixed results.
To find out more, a quartet of researchers led by David Batty of University College London examined raw data from 16 long-term studies, covering 163,363 people aged 16 and over.
Participants were monitored for an average of nearly a decade. More than 4,300 died of cancer.
- Chicken or egg? -
The team sifted through raw data on psychological distress levels, lifestyle habits and cancer incidence.
They searched in particular for evidence of links between stress and cancers related to hormonal changes or lifestyle.
Depression is known to disrupt hormonal balance to the extent of boosting natural cortisone concentrations and inhibiting DNA repair mechanisms, both of which weaken cancer defences.
It is also well established that people who are down in the dumps are more likely to smoke, drink and become obese -- all associated with a higher cancer risk.
The team found that regardless of one's lifestyle, people who described themselves as depressed were nearly twice as likely to dies of colon cancer, and more than twice of likely to succumb to pancreas or oesophagal cancer. The rate for leukaemia was even higher.
The team could not discount that depression may be a result, rather than the cause, of cancer.
"Distress might be a consequence of the early stages of the malignancy rather than a potential predictor," they noted.
If someone is sick, in other words, even if unaware they have cancer, the symptoms are likely to dampen their spirits.
More research is needed to confirm the link, and tease out the causal connections, said Batty.