Large research studies including tens and hundreds of thousands of subjects have been pivotal in increasing the medical world's understanding of what causes problems such as heart disease. Now, one of those large studies, the Women's Health Initiative, has revealed new evidence about heart rate and the risk of heart disease.
Doctor Judy Hsia from George Washington University examined data about 160,000 women who have been part of the WHI for eight years.
Hsia says the study collected detailed baseline information on the women and includes subjects from diverse socioeconomic and ethnic backgrounds.
"We have for instance… do they have high blood pressure, smoking, and so on," Hsia says. "But we [also] have things like the types of exercise they did and the duration and frequency of physical activity. We have very detailed dietary information. We have depression and anxiety data. So these are all things that can affect heart rate."
Hsia found that women who have faster resting heart rates - especially those whose hearts beat more than 76 times per minute while they were resting - were more likely to have a heart attack.
"The 20 percent of people with the highest heart rate, which in our group was above 76 beats per minute… they had a 26 percent higher likelihood of having a heart attack or coronary death, compared to everybody with the lower heart rate," Hsia says.
Hsia points out that it's possible to lower one's resting heart rate with regular exercise, such as running or swimming or even dancing. But she says this finding about heart rate was independent of whether women were physically fit.
Aside from fitness, Hsia explains that heart rate is determined by a variety of factors, including the amount of adrenaline a person naturally produces.
"There are people who have a higher natural level on the adrenaline, and so it may be that people who have higher setting on the adrenaline side are at higher risk for heart disease, and they also have a higher heart rate," she says.
"It's not that the heart rate causes heart disease. It's that they both are reflecting the same underlying situation."
Hsia says that rapid resting heart rate is only one indicator of cardiac risk. Women with higher heart rates can lower their overall risk by changing their behavior by staying physically fit, eating a prudent diet, not smoking and keeping the weight off.
Hsia's article is published in the British Medical Journal.
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