People who suffer from anxiety could have a higher risk of developing severe cancers, research has shown.
The study – which was published in PLoS One and conducted by scientists at the Stanford University School of Medicine – involved exposing hairless mice to ultraviolent light.
It revealed those who were particularly risk-averse and reticent developed a larger number of invasive cancers and tumours than their relaxed counterparts.
Researchers found the nervous creatures had a higher number of regulatory T cells, which can suppress the immune system.
They were also creating fewer of the chemical signals known to cause the human body to fight tumours.
Expatriates who are susceptible to feeling nervous could find even more benefits from having international medical insurance, as anxiety was linked to a dampened immunity and sensitivity to the health impacts of stress.
In the future, the researchers wish to examine whether the efficacy of cancer treatments can be altered by calming down patients.
Stress expert, immunologist and first author of the study Firdaus Dhabhar hypothesised that prescribing valium or other anxiety medications to cancer sufferers could potentially improve their outcome.
"Ultimately, we really want to harness the patient's mind and body while doing everything that medicine can from the outside to maximize treatment success," he declared.
Previous work conducted by the expert had investigated the difference between 'good' and 'bad' stress.
Short-lived experiences, such as delivering presentations or being chased by lions, could have positive effects on the human body by initiating a fight-or-flight response.
However, long-term stressors can damage the immune system's ability to combat diseases over time, Mr Dhabhar remarked.
According to the Mayo Clinic, stress results in the release of hormones such as cortisol, which puts a person at an elevated risk of suffering from a wide range of health problems.
These include digestive complaints, sleeping issues, heart disease, depression, memory impairment and obesity.