TUESDAY, Dec. 20 (HealthDay News) -- A rise in resting heart rate during middle age signals an increased risk of dying from heart disease, new research indicates.

People whose heart rates increased from under 70 beats per minute to more than 85 beats per minute over 10 years had a 90 percent increased risk of dying from heart disease compared to people whose heart rates stayed around 70 beats per minute, according to the large study.

"Resting heart rate is one of the simplest measures in medicine and everyone can do that by themselves at home. From cross-sectional studies, it is known that a person's resting heart rate is related to the relative risk of premature cardiovascular disease and death. However, it has not, before now, been associated with an increased risk of premature cardiovascular death," said study senior author Ulrik Wisloff, director of the K.G. Jebsen Center of Exercise in Medicine in Trondheim, Norway.

"Our observations suggest that resting heart rate may be an important prognostic marker for ischemic heart disease and total mortality," said Wisloff, who added that changes in resting heart rate may signal the need for lifestyle changes.

Results of the study are published in the Dec. 21 issue of the Journal of the American Medical Association.

Wisloff said that factors that can influence heart rate include genetics, age, activity level, diet and whether or not someone smokes.

The current study included nearly 13,500 men and 16,000 women. The study participants, all of whom lived in Norway, had no known heart disease at the start of the study. The average age of participants was about 52 years at the start of the study.

Resting heart rate measurements were taken at the start of the study, and then again about 10 years later. After 12 years of follow-up, 3,038 study participants had died. Nearly 400 deaths were from heart disease.

Compared to people whose heart rate was consistent at less than 70 beats per minute at both readings, those whose rates increased from less than 70 beats per minute to more than 85 beats per minute had a 90 percent higher risk of death from heart disease. In those whose heart rates started at between 70 and 85 beats per minute, an increase to more than 85 beats per minute at the follow-up reading signaled an 80 percent increase in the risk of heart disease mortality, reports the study.

Wisloff said the change in heart rate may signal underlying heart disease that is currently going unrecognized.

Dr. Harmony Reynolds, associate director of the Cardiovascular Clinical Research Center at the NYU Langone Medical Center in New York City, said there are likely multiple factors that cause the increase in heart rate. One might be obesity, which she said puts more demand on the heart and circulatory system.

It's not clear from this study whether reducing resting heart rate will reduce the risk of death. People who started with a resting heart rate above 85 didn't see a benefit from reducing their heart rate in this study. But, people whose heart rates started between 70 and 85 beats per minute who were able to lower their resting heart rate to below 70 beats per minute decreased their risk of dying from heart disease by 40 percent, according to Wisloff.

Reynolds said she was surprised to see the group that didn't benefit from lowering their heart rate over time.

In general, she said, a slower pulse is an indicator of better heart health. For people who'd like to improve their heart health, she said the standard advice still holds true. "It's always beneficial to increase your fitness level, so exercise more. Maintain a healthy weight, and eat healthier foods, and don't smoke," she advised.

Wisloff said that people should know their heart rates over time. And, if you see changes, let your doctor know. "It's easy, free and it may be important to you," Wisloff said.

More information

Visit the U.S. National Library of Medicine to learn how to take your pulse and find your resting heart rate.