Being shy and reluctant to take chances may keep you from meeting new people or changing careers, but could it also give you cancer?
That seemingly farfetched link is one focus of a University of Chicago research group that is trying to understand how temperament may affect a wide range of health yardsticks. Some experts refer to the discipline by the unwieldy name of psychoneuroimmunology.
The U. of C. group's most recent results, published last month in the journal Hormones and Behavior, suggest the relationship between shyness and cancer is real, though the study could not draw firm conclusions about why that is.
In this case, the medical payoff may have to await details that no one has yet nailed down. It's a commonly accepted idea that many bad health effects can stem from everyday stress. For chronically shy people, stress may arise simply from having to deal with unfamiliar situations.
But experts still are unsure how that process actually plays out in the body, said Jason Yee, a graduate student in comparative human development and co-author of the U. of C. paper.
"If we're going to find ways of improving health by improving psychological states, the best way is to accurately characterize what's going on," said Yee, who works with professor Martha McClintock, director of the U. of C.'s Institute for Mind and Biology.
Working the room
The study began by measuring how willing individual female rats were as infants to explore an unfamiliar room. Researchers ranked the rats according to whether they were adventurous or timid in examining the room.
The rodents all belonged to a strain that is prone to developing spontaneous mammary and pituitary tumors. But the team found that the rats that were timid as infants developed tumors sooner than the more daring rats and died about six months sooner.
That outcome seemed to fit what the researchers had seen in an earlier study of male rats, for whom shyness also was linked to shorter life spans, though that study did not address cancer susceptibility. As it turned out, the link between shyness and cancer in females wasn't as clean as the team expected.
In theory, temperament has the potential to affect health through a straightforward causal chain. Apprehensive animals probably experience more stress in new situations, which would lead them to release more "stress hormones" that can damage cells and tissues. Over time, such responses could foster the genetic breakdowns that cause cells to go haywire and become cancerous.
The problem was that the shy rats didn't have higher levels of stress hormone than the freewheeling rodents. They had less.
"It's one of those results that sort of sends you back to the drawing board," said study co-author Sonia Cavigelli, a former U. of C. graduate student who now teaches biobehavioral health at Penn State University.
One possibility is that the U. of C. team was looking in the wrong place for what caused the rats' aggressive tumors.
Stressed out
A study published last June in the journal Nature Medicine by a group at the University of Texas suggests chronic stress can abet tumor growth by encouraging the spread of blood vessels that feed tumors, a process called angiogenesis.
But the U. of C. team believes they may have found some clues within their own data. The rats that were more apprehensive also tended to have more irregular menstruation during adolescence. That could have skewed their levels of reproductive hormones, which can feed mammary tumors.
What caused the erratic menstrual cycles? The researchers don't know, but it could be that instead of shyness causing cancer, a separate aspect of the rats' physiology has a dual effect: It makes them shy and raises the risk of cancer.
"Let's just suppose there's a gene that's linked to behavior and development of tumors," Cavigelli said. "If that's the case, the behavior here doesn't really cause tumor development."
Yee and his colleagues in McClintock's lab are still investigating the link. Yee said that while the absence of a clear story about stress hormones was frustrating, he hopes the follow-up studies will solve the problem.
"The wonderful thing is that sometimes you get results in the opposite direction from what you expect, and it leads to new insights," Yee said. "This is how biology speaks to you."
