Psychological stress linked to cancer.

As if the sagging economy and rush-hour commuting weren't stressful enough, here comes a provocative pair of studies to add to your worries. They indicate that psychological stress may increase an individual's risk of developing certain cancers.

Two years ago, Australian researchers reported that stressed-out individuals might face an increased risk of colorectal cancers -- malignancies that each year strike an estimated 152,000 people in the United States alone. Hoping to verify that link, Joseph G. Courtney of the University of California, Los Angeles (UCLA), School of Public Health and his co-workers joined forces with researchers in Sweden who had access to a large database on Stockholm-area patients with colorectal cancer.

The researchers recruited 569 of these men and women for their study, along with 510 randomly selected cancer-free adualts. Each of the study's participants then answered a series of questions about stressful events.

In the September EPIDEMIOLOGY, Courtney's team now confirms that severe on-the-job aggravation appears to put people at increased risk of developing colon and rectal cancers. Those who reported a history of workplace problems over the past 10 years faced 5.5 times the colorectal-cancer risk of adults who reported no such problems.

That association held even after the researchers accounted for diet and other factors that had previously been linked to these malignancies. Unpublished research by the UCLA team also hints that individuals who toil in high-pressure situations while processing little or no control over workplace decisions face the highest risks.

In a second new study, Japanese researchers report finding cellular changes in psychologically stressed animals that may explain how anxiety might foster cancer.

For their investigations, Shuichi Adachi and his co-workers at Saitama Medical School in Moroyama caged sets of 30 young rats in a "communications box." The box is laid out like a checkerboard, with half the rodents -- those in the chambers corresponding to the red squares, for instance -- receiving periodic electrical shocks over a 5- to 10-hour period. The study then monitored how nonshocked animals, in cages corresponding to the black squares, responded biochemically to the psychological stress induced by watching, listening to, and smelling the torment of their neighbors.

In terms of the amount of altered DNA in their tissues, nonshocked rats that had completed one day of tests were no different from animals that had never participated in the psychological testing. But nonshocked rats that endured two to four days of such tests developed sharply elevated concentrations of 8-hydroxy-2'-deoxyguanosine in the DNA of their livers.

This oxidative change, known as a DNA lesion, occurs spontaneously in the target organs of animals exposed to carcinogens, radiation, or an overabundance of free radicals -- biologically damaging chemical agents possessing one or more unpaired electrons.

The stress-induced increase in the number of lesions in liver DNA "must be interpreted as [caused by] excess generation of reactive oxygen species," Adachi's team concludes in the Sept. 15 CANCER RESEARCH. As such, they report, it constitutes "the first evidence that oxidative damage to nuclear DNA is induced by psychological stress."

The rats appeared to be able to repair most of the stress-induced lesions within an hour. However, numerous studies have shown that as animals age, they tend to accumulate such oxidative lesions in their DNA. And in the Sept. 1 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES, Bruce N. Ames and his co-workers at the University of California, Berkeley, review the cancer significance of those lesions. If present when a cell divides, they note, "an unrepaired DNA lesion can give rise to a mutation" -- and ultimately a malignancy.

Nor is the liver the only organ vulnerable to stress-mediated cancers, Adachi's team reports. The Saitama researchers note that mice psychologically stressed every other day for four months proved more susceptible to urethane-induced lung tumors than unstressed animals exposed to this carcinogen.

The Japanese study offers a "superior model" of psychological stress in humans, Courtney told SCIENCE NEWS.

Scientists know that stress can trigger the body's "fight-or-flight" response, in which the adrenal glands churn out powerful hormones that divert blood flow from internal organs (such as the intestines or liver) to the brain, muscles, and heart. Once the danger subsidies, blood rushes back into the oxygen-starved internal organs, Courtney says. That burst of oxygen-rich blood may lead to increased production of free radicals -- and DNA lesions.

In addition, stress weakens the immune response, Courtney says. A vigorous immune response should kill damaged cells. Hiwever, if the immune system is compromised, a malignant cell might escape, spawing a tumor, he suggests.