An eight-year study of more than 6,500 adults found a 20 percent to 30 percent higher death rate among patients who initially reported pain in all or part of the body compared with those who did not. And almost all those deaths were due to cancer, report researchers led by Gary J. Macfarlane of the University of Manchester's Chronic Disease Epidemiology Unit. The findings appear in the Sept. 22 issue of the British Medical Journal.
The researchers say the difference is hard to explain, even after accounting for risk factors including age, sex and smoking. "Future studies are needed to confirm this association and investigate the possible mechanisms," they write.
It is "a curious finding," and one that needs confirmation by a similar study in a different population, says Iain K. Crombie, professor of public health at the University of Dundee in Scotland and author of an accompanying editorial.
It's premature to tell doctors to treat pain differently than they do now, Crombie says. "At this stage, it is unwise to change clinical behavior on the basis of one finding," he says.
"What plausible biological mechanism could explain the finding?" Crombie writes. "The authors mention psychosocial factors, lifestyle factors and neuroendocrine factors but do not explain how these could have a carcinogenic effect on all body systems."
But at least part of the answer can be found in a decade-old article in Pain, the journal of the International Association for the Study of Pain, says Louisa E. Jones, executive officer of the association.
That article, titled "Pain Can Kill," was written by John C. Liebeskind, a psychologist at the University of California at Los Angeles (UCLA). He cited studies showing that "pain and stress can inhibit immune function and enhance tumor growth," and laboratory work showing that the activity of cancer-fighting immune cells was lessened in animals given painful electrical shocks.
"It appears that the dictum 'pain does not kill,' sometimes invoked to justify ignoring pain complaints, may be dangerously wrong," Liebeskind wrote. He has since died of cancer.
A large part of Liebeskind's evidence was based on research by Gayle G. Page, then working for her doctorate at UCLA and now an associate professor of nursing at Johns Hopkins University School of Medicine.
In her studies, in which animals with cancer were exposed to pain, Page says that "masking the pain reduced the susceptibility to cancer progressing."
Pain is closely associated with depression in humans, Page says. "If someone with cancer is having pain, and that pain is not relieved, it could cause depression that causes changes in the endocrine [hormone] system," she says. "That physiological change makes the person more susceptible to having cancer progress. There is a vicious cycle between pain and depression."
Whatever its role in cancer prevention, pain relief is a vital part of cancer treatment, says Liebeskind's editorial. "Failing to relieve pain in cancer patients might also be expected to have cancer-promoting consequences that do not abate with time," he writes.
What To Do
Anyone, sick or well, who experiences chronic pain should ask a physician about the best way to get relief and how to find the cause.