How fast can you run? Researchers say that the speed with which you can cover a mile in middle age may predict how heart healthy you'll be as you grow old.

And it's not just one set of scientists who have reached that conclusion. Recently, researchers at the Cooper Institute in Dallas and another set from the University of Texas Southwestern Medical School looked at more than 66,000 people and concluded that looking at fitness level in midlife said as much about future long-term heart health as cholesterol, high blood pressure and other standard measures.

What they chose as a simple-to-understand measure was the speed at which one could run a mile.

The Cooper Center Longitudinal Study results were published in The Journal of the American College of Cardiology. The researchers, including some collaborating from Stanford and Northwestern universities, looked at cardiovascular fitness levels in men at ages 45, 55 and 65. They followed their 11,049 subjects until they died or they reached age 90. The deaths were categorized by whether they were cardiovascular or not. Median follow-up was just over 25 years.

To assess the fitness, they put each subject on a treadmill and then categorized them based on how fast they ran into low, moderate or high fitness. What they found was that differences in fitness levels translated into "marked differences in the lifetime risks for CVD death at each index age." Low fitness vs. high fitness at age 45 was 13.7 percent vs. 3.4 percent. At age 55, it was 34.2 percent vs. 15.3 percent. And at age 65 it was 35.6 percent vs. 17.1 percent.

Their conclusion: "A single measurement of low fitness in mid-life was associated with higher lifetime risk for CVD death, particularly among persons with a hugh burden of CVD risk factors."

The other study, led by researchers at Southwestern, also involved Cooper and Stanford. And it set out to take the knowledge that fitness is associated with heart disease and answer questions about how much fitness improves risk classification.

They looked at more than 66,000 people enrolled in the Cooper study over 36 years and estimated the risk of CVD mortality both with and without fitness considerations, using a traditional risk factor model that included age, sex, blood pressure, whether there was diabetes, total cholesterol and smoking.

And they, too, concluded that "a single measurement of fitness significantly improves classification of both short-term (10-year) and long-term (25-year) risk for CVD mortality when added to traditional risk factors."

"When you try to boil down fitness, what does fitness mean?" said Dr. Jarett D. Berry, assistant professor of internal medicine and cardiology at Southwestern Medical School and a co-author of both papers, in an interview with Tara Pope of the New York Times. "In both these studies, how fast you can run in midlife is very strongly associated with heart disease risk when you're old. The exercise you do in your 40s is highly relevant to your heart disease risk in your 80s."

Berry noted that running a mile in 8 minutes or less designated a man as highly fit, while at 9 minutes or less he was only moderately so. A woman who can run a mile in 9 minutes or less is highly fit, in 10.5 minutes or less is moderately so. A man who takes longer than 10 minutes or a woman who takes longer than 12 shows a poor level of fitness. With each minute longer, there's a dramatic increase in heart risk, the research shows.

But Berry also warned that how fast you run a mile should not be considered an acceptable measure of risk without more study. It was chosen partly because it's something to which people relate.

Run time has been deemed an acceptable measure of fitness for a very long time. For example, according to, "The 12 Minute Run fitness test was developed by Dr. Ken Cooper in 1968 as an easy way to measure aerobic fitness and provide and estimate of VO2 max for military personnel. This simple test is still used today as a field test for determining aerobic fitness."

The VO2 is a measure of how well someone uses oxygen while exercising. And exercising, experts agree, is key to heart health.