Think twice before having a spat with your spouse, especially if one of you is injured.
The stress from even a 30-minute argument can increase healing time by up to one day, according to a study in the current issue of the Archives of General Psychiatry.
The research is important because it explains a mechanism for why this can occur, said Cinnamon Stetler, a psychology researcher at the University of British Columbia.
It is "bringing the real world of marriage into the lab," said Stetler, who was not involved in the research.
Marital studies have been ongoing since the 1980s at Ohio State University's Institute for Behavioral Medicine Research.
They have found that more-hostile couples have a greater production of stress hormones, said Janice Kiecolt-Glaser, the lead researcher at Ohio State and a professor of psychology and psychiatry.
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She has been studying wound healing since the 1990s and found that there was a clear effect of stress.
Kiecolt-Glaser is now combining the two studies and examining how marital stress affects wound healing.
The researchers selected a group of 42 married couples who met strict health requirements.
At the institute, the couples made two 24-hour visits that were two months apart.
At the start and end of each visit, the participants gave blood to measure systemic levels of pro-inflammatory cytokines, which are proteins important to healing and inflammation.
Eight superficial blister wounds
Local cytokine production is good for healing, whereas systemic circulation of cytokines is not good news, said Kiecolt-Glaser. This is because cytokines increase inflammation, which is linked to a variety of diseases: heart disease, arthritis, osteoporosis, type 2 diabetes and cancer.
For the wound-healing part of the study, the researchers applied a suction device that created eight pea-sized blisters on each participant's forearm. The blister wounds were superficial.
A chamber covered the blisters to collect the person's serum, which was used to measure cytokine levels.
They measured wound temperature and humidity, keys to healing.
After they removed the chamber, they assessed the blister wounds daily for eight days and again on day 12.
To study marital stress, husbands and wives individually completed questionnaires on their marriage.
Then during the first visit, the couples were directed to focus on positive and supportive interactions. Each husband or wife was asked to talk for 10 minutes about something they would like to change about themselves, with the condition that it couldn't relate to the marriage itself. People commonly talked about being more organized and losing weight, Kiecolt-Glaser said.
One man who particularly stood out wanted to be more patient with his children, said Timothy Loving, an assistant professor of human ecology at the University of Texas.
30 minutes of arguments
At the second visit, the researchers used the questionnaire information to get the couples to argue for 30 minutes.
Common themes were finances, in-laws, free time and children, Kiecolt-Glaser said.
Loving asked, "If I was a fly on the wall, what would I hear when you are discussing this?"
The researchers taped both the supportive and argumentative interactions and used the Rapid Marital Interaction Coding system to distinguish between the distressed and non-distressed couples.
To put people in a situation where their interactions can be studied and objectively classified is a major strength of the research, said Kenneth Freedland, a professor of psychiatry at Washington University in St. Louis. Freedland was not involved in the research.
The results of the study show that "stress is more important than we thought," Kiecolt-Glaser said.
After argumentative interactions, blister wounds healed more slowly than after supportive interactions. The local level of cytokines, which promote healing, was also lower. Couples with high baseline hostility had higher circulating levels of cytokines the morning after an argument than couples with low baseline hostility.
