Moderate Aggression May Lead To Stronger Immune Systems

"We have observed this relationship in animal studies but this is the first time that a connection has been made between aggression and immunity in humans," according to Douglas Granger, associate professor of biobehavioral health in Penn State's College of Health and Human Development.

Granger, Alan Booth, Distinguished Professor of Sociology and Human Development and Family Studies at Penn State, and David R. Johnson, professor of sociology at the University of Nebraska, published their findings in "Human Aggression and Enumerative Measures of Immunity," in the current issue of Psychosomatic Medicine, the professional journal for the American Psychosomatic Society.

"Our study suggests that differences in people's aggressive behavior influences how their immune systems are prepared to deal with infections, viruses and bacteria," says Booth.

Men who have been in occasional fights or been in trouble with the law, either as an adult or youth, have immune systems that may be ready to marshal a more rapid and intense response to pathogens associated with disease or injury than do men who are seldom aggressive, according to the researchers. "However, higher levels of aggression do not convey additional immune benefits," says Booth.

The researchers studied a sample of 4,415 men aged 30 to 48 years who were interviewed to determine their level of aggressive behavior. The subjects then underwent medical examination to determine their state of health. The researchers also took blood samples from each subject. Those samples were then analyzed for different types of white blood cells or lymphocytes.

"White blood cells are major players in the body's immune system," explains Granger. Out of eight enumerative indicators of immune activity studied, two specialized types of lymphocytes (CD4 cells and B cells) that determine the initiation, magnitude, and duration of specific cellular immune responses were present in high concentrations in the circulation of moderately aggressive men. The activity of these particular lymphocytes, which includes antibody production and secretion of intercellular signals that turn the immune response on or off has considerable value for increasing the chances of survival in a pathologically challenging environment, says Granger.

According to the study, individuals who reported engaging in two aggressive acts were 30 percent more likely to be in the top quartile of CD4 cell numbers than those reporting no aggressive acts, after taking into account current health risks and problems that might be stimulating the immune system. Men reporting five aggressive acts were seven percent more likely to be in the top quartile than those reporting three aggressive acts. Those with eight aggressive acts were only four percent more likely to be in that category than those reporting six aggressive acts. Increases in aggressive behavior did not convey correspondingly higher odds of being in the top quartile. A parallel pattern was observed for B lymphocytes.

Men reported on 12 different acts of aggression ranging all the way from playing hooky twice a year or more to fights involving weapons. Twenty-two percent reported no aggressive acts. Thirty-nine percent reported, one to two aggressive acts, 27 percent indicated three to five, and 12 percent recorded six or more aggressive acts.

"The strength of the finding is that we controlled for all types of factors that could impact the subjects' immune systems, such as whether the subjects smoked or consumed alcohol, their level of health and their testosterone scores," says Booth. "While testosterone was associated with aggressive behavior, it was not the hormone that accounted for the higher immune cells found among aggressive men."

The researchers explain that aggressiveness was seen throughout history as being vital for gaining access to food, protecting the young, battling predators, and fighting other communities over resources and territory. Engaging in aggressive behavior, however, has a high likelihood of leading to trauma, wounds, and exposure to new diseases.

Foraging, hunting, and war may require travel far from home. Isolated from nursing care and the protection of the home community, individuals benefit if their immune system more effectively recognizes and mobilizes its components to eliminate pathogens, says Booth. In addition, individuals benefit if their immune system promotes efficient recovery from disease, facilitates repair of tissue damage wounds, and records immunologic history to be prepared to respond more efficiently if subsequent reexposure occurs.