NEW ORLEANS — Hostility is linked to poor heart health, and a new study reveals what may happen in women's bodies that may explain this link.

Scientists have known that, in women, optimism is associated with a reduced risk for heart disease, and that "cynical hostility" — or a general mistrust of other people — has been linked to a higher risk for heart disease, according to a previous study.

What has been unclear, however, is what mechanism optimism and hostility act through to influence women's heart health. In other words, why do these traits have such effects on heart disease risk?

In the new study, the researchers showed that the missing link could be something called heart rate variability, said Dr. Elena Salmoirago-Blotcher, an epidemiologist and assistant professor of medicine at Brown University School of Medicine and the lead author of the study. Salmoirago-Blotcher is also a research scientist at the Miriam Hospital Centers for Behavioral and Preventive Medicine. 

The study revealed that women with higher levels of hostility had a lower heart rate variability, on average, compared with women with lower levels of hostility.

Heart rate variability is a measure of how much the time interval between heart beats varies from moment to moment, Salmoirago-Blotcher told Live Science. A person's heart rate is not steady, rather, there can be tiny variations in the interval between beats, Salmoirago-Blotcher said.

In general, a higher heart rate variability is a good thing, Salmoirago-Blotcher said. It shows that the part of the nervous system that speeds up the heart rate and the part that slows it down are working in balance, she said. For example, research has shown that women with depression have a lower heart rate variability, Salmoirago-Blotcher said. Salmoirago-Blotcher presented her findings here Monday (Nov. 14) at the American Heart Association's Scientific Sessions annual meeting. 

Hostility and heart health

In the new study, the researchers looked at data on more than 2,600 women who were enrolled in a study called the Myocardial Ischemia and Migraine Study (MIMS). MIMS was a part of the Women's Health Initiative (WHI). The women in the study were, on average, 63 years old.

As a part of the MIMS study, the women had their heart's electrical activity measured an electrocardiogram (ECG or EKG) test. In the new study, the researchers used this data to calculate their heart rate variability. In addition, the researchers had data from the WHI about how optimistic and hostile the women were, based on their answers to two questionairres.

Hostility may increase the activity of the part of the nervous system that revs up a person's fight or flight response, Salmoirago-Blotcher said.

Salmoirago-Blotcher noted that the researchers found that the women in the study who were more hostile were also more likely to have high blood pressure, high cholesterol and obesity, compared with those who were less hostile.

The researchers did not find a link between optimism and heart rate variability, but in earlier studies, optimism has been found to be associated with better heart health, Salmoirago-Blotcher said. It may be that factors other than heart rate variability account for the link between optimism and heart health, including behavioral factors, she said. 

For example, in the study, the women who were more optimistic were more likely to have fewer risk factors for heart disease and get more physical activity than those who were less optimistic, Salmoirago-Blotcher said. Physical activity has been shown to be associated with greater heart rate variability, she added.

The study had several limitations, Salmoirago-Blotcher noted. First, the study was observational, meaning that the researchers cannot prove cause-and-effect. Second, the researchers did not adjust the findings for depression and physical activity levels, she said. In other words, it is unclear how much of a role these factors played in the results, she said. More research is needed to confirm the findings.

The study has not been published in a peer-reviewed journal.

Originally published on Live Science.