We know that stressful experiences are bad for health, but it is your reaction to stress -- not how often you're stressed -- that is more important to heart health, says a new study.

To study the effect of stress on heart health, researchers from Penn State University and Columbia University wanted to research further into the effect of daily stress on heart rate variability -- the variation in intervals between heartbeats, which is linked to cardiovascular disease. Heart rate variability is important, explains Nancy L. Sin from Penn State, because "higher heart rate variability is better for health as it reflects the capacity to respond to challenges. People with lower heart rate variability have a greater risk of cardiovascular disease and premature death."

For their research, the team collected data from 909 participants aged 35 to 85 who had taken part in a national study. Participants were questioned on their stressful experiences via daily telephone interviews over an eight day period, and had their heart's activity measured using an electrocardiogram.

During the interviews, the participants reported on the stressful experiences they had encountered that day, and rated each experience as having been "not at all stressful," "not very stressful," "somewhat stressful" or "very stressful."

They also reported on any negative feelings they had experienced during the day.

The interviews showed that participants experienced on average at least one stressful experience on nearly half of the interview days (42 percent), with these stressful experiences generally rated as having been "somewhat" stressful.

From these reports, the team saw that it wasn't necessarily those who reported a high number of stressful events in their lifetimes that had the lower heart rate variability. It was actually those who perceived the events as being stressful -- no matter how many they experienced -- who had more negative emotions and showed a lower heart rate variability, therefore putting them at a higher risk of heart disease.

"These results tell us that a person's perceptions and emotional reactions to stressful events are more important than exposure to stress per se," says Sin. "This adds to the evidence that minor hassles might pile up to influence health. We hope these findings will help inform the development of interventions to improve well-being in daily life and to promote better health."