(CNN) -- "A sad soul can kill you quicker, far quicker, than a germ," John Steinbeck once wrote. Now we are closer to understanding why.
A disease like cancer can be a mortal battle, often fraught with overwhelming stress. Given that stress management can be difficult even under ordinary circumstances, elevated feelings of anxiety and depression in cancer patients are certainly understandable.
Yet, several recent studies underscore how critically important it is for those fighting illness to learn how to combat stress.
A team of researchers led by Lorenzo Cohen, professor of general oncology and director of the Integrative Medicine Program at The University of Texas MD Anderson Cancer Center, found that symptoms of depression among a group of patients with late-stage renal cell carcinoma were associated with an increased risk of death. The study was published in the journal PLOS ONE in August.
The chief suspects in Cohen's study: cortisol -- also known as the "stress hormone" -- and inflammatory pathways.
"This study is the next step in the process of understanding that emotional factors have an impact on biology, which can, in turn, influence outcomes in cancer," says Cohen.
Cortisol is the hormone produced by the adrenal gland in response to stress. It helps regulate the inflammatory response in the body.
According to Cohen, under normal circumstances cortisol levels should be high in the morning and drop throughout the course of the day. But among patients experiencing chronic stress or depressive symptoms, cortisol levels can remain sustained throughout the day, with less of a decrease in the evening.
In the study, those patients with sustained cortisol levels throughout the day had an increased risk of mortality. Through gene profile analyses of patients, the researchers documented that the association between patient psychological condition and survival time may stem from a dysregulation in inflammatory biology.
Two other studies on how stress influences other illnesses shed further light on this process.
A team of researchers led by Sheldon Cohen (not related to Lorenzo Cohen), professor of psychology and director of the Laboratory for the Study of Stress, Immunity and Disease at Carnegie Mellon University, found that chronic psychological stress was associated with the body losing its ability to regulate its inflammatory response.
The researchers found that over a prolonged period of chronic stress, body tissue becomes desensitized to cortisol and the hormone loses its effectiveness in regulating inflammation. Inflammation is a good thing when it's triggered as part of the body's effort to fight infection, says Lorenzo Cohen, but chronic inflammation can promote the development and progression of many illnesses, including depression, heart disease, rheumatoid arthritis, diabetes and cancer.
One of the challenges in this type of research is that causation between psychological stress and cancer survival is notoriously hard to pin down. You cannot, after all, ethically heckle a group of cancer patients just to monitor their stress response.
But a growing body of research from scientists studying ovarian, breast and other cancers continues to cement the link between psychological stress and disease, metastatic growth and survival. It also suggests that stress management should be an integral part of the treatment for cancer and perhaps even all inflammatory diseases.
According to Lorenzo Cohen, the next step is to conduct clinical trials by taking a population of cancer patients who meet the criteria for depression and anxiety, treating their mood disorders and seeing whether outcomes are improved, compared to a control group that does not receive the same treatment.
In the meantime, Cohen urges cancer patients to try to manage in some fashion the stress associated with a life with cancer.
For some individuals, that may mean turning to psychiatry or cognitive behavioral therapy or perhaps a more pharmacological approach, he says.
Yet others may turn to mind-body medicine and consider practices such as meditation, yoga, tai chi, self-hypnosis or guided imagery -- all of which have been shown to be quite useful in helping to manage stress.
Managing stress, alongside conventional treatment and a full lifestyle programmatic approach, may ultimately improve outcomes, says Cohen.
"We certainly know it improves patient's quality of life. Now we need to do more research to see if modifying diet, increasing physical activity and managing stress can also prolong survival."