The average age of the participants was 63 years old. They were mostly middle-class white couples who had no history of cardiovascular disease.
About 30 percent of the participants were viewed by their spouse as a source of positive support, whereas 70 percent were viewed by their spouse as ambivalent.
"You typically don't find long-term married couples who are truly negative toward each other," Uchino explained. "Usually those relationships get ended along the way."
But ambivalence isn't beneficial in relationships either.
"People who feel ambivalent toward their spouse are not able to approach that person for support because they are not certain of what to expect," Uchino said. "That person could be positive but they could also be negative."
Essentially, they are not getting support from a really important relationship in their life, he said.
Even if the person goes to an ambivalent spouse for support, the spouse may behave in ways that increases their stress, Uchino said.
Dr. Michael Sheridan, a cardiac surgeon with Indiana University Health Arnett in Lafayette, said the findings in the study make sense.
"Although the study doesn't prove it raises coronary calcification scores, if you are upset over your spouse during times you feel you need to have support then your stress levels go up," he said.
When stress levels elevate, it can worsen already known cardiovascular risk factors such as high blood pressure, diabetes, and high cholesterol. Stress can also be a negative influence on people who smoke, and smoking is also a risk factor for heart disease.
Stress also affects the immune system by causing inflammation in the body, which can lead to an increased risk of plaque formation in the arteries.
Also, ambivalent relationships are more difficult to navigate emotionally, because it differs from viewing someone as completely negative, Uchino said.