Even In Your 20s, Fitness Cuts Risk For Later Heart Disease, Major Study Finds

Feeling a bit bloated and sluggish after Thanksgiving weekend? A major study just out in the journal JAMA Internal Medicine offers an added nudge to get back on the exercise wagon. How fit you are even in your 20s, the study finds, can dramatically affect your risk of heart disease and death well into middle age.

So dramatically, in fact, that every minute matters.

Imagine you're doing a stress test on a treadmill. Every two minutes, the machine makes you go faster and at a steeper incline. The first few minutes are no sweat — you're walking, then trotting, then jogging — but soon you start to suck air, and finally hit the point that you can bear no more. (Or you may reach the 18-minute maximum, if you're superhuman.)

Say you did that test in your 20s. Now fast-forward 25 years. The study found that every extra minute you could last on the treadmill meant you were at a 15 percent lower risk of death over that quarter-century, and at a 12 percent lower risk of harmful effects of heart disease, including stroke and heart attack.

"That's a lot," I found myself saying in a phone interview with the study's two lead authors, Dr. Ravi V. Shah, of Harvard Medical School and Beth Israel Deaconess Medical Center, and Dr. Venk Murthy of the University of Michigan.

"We were surprised too," Dr. Shah said.

"Two, three, four, five minute differences are not uncommon," Dr. Murthy said. "That adds up. That's 15 percent per minute — it's pretty substantial."

Though, of course, it must be noted that the overall risk of heart disease and death are relatively low in such a young population. Among the 4,872 people in the study, 273 died, but 200 of those deaths had no relation to heart disease. And just 4 percent of the study's subjects had a "cardiovascular event" like a heart attack.

Still, the results cast new light on just how much fitness matters for heart health — even in our 20s, when many of us can still get away with a sleepless all-nighter or an all-weekend TV binge.

This new research is the first large study to examine people in their 20s onward over such a long period, the lead authors say, and underscores the importance of starting good fitness habits early — not just in later years, when the health price of inactivity is already well known.

The study also found that the heart benefits of fitness held true independent of weight and other heart risk factors. That suggests, Dr. Shah said, that "being fit is important for everyone, not just for people who are trying to lose or maintain weight."

The study — an epic endeavor that began back in the mid-1980s and was led by four universities, including Harvard and Johns Hopkins — also suggests that early trajectory matters. That is, typical as it may be, it is not a good idea to let your fitness decline in your 20s.

Nearly 2,500 of the subjects underwent a second treadmill test just seven years after the first. For every minute less that they could last compared with their first test, their risk of death in the coming years went up by 21 percent, and their risk of heart disease by 20 percent.

And one other, particularly fascinating finding: Fitness as reflected by treadmill performance did not seem to matter for an accepted measure of heart health, the accumulation of calcium deposits in the arteries that supply the heart.

Drs. Shah and Murthy explain in an email:

"Calcium score” is something that we measure on a CAT scan that reflects how much calcium is deposited in the arteries that supply the heart (the coronary arteries). A higher calcium score is taken to indicate a higher burden of coronary artery disease, and many studies have found that calcium score is associated with poorer cardiovascular health and outcomes.

One would expect that greater fitness would therefore be related to a lower calcium score or absence of calcium in the arteries. We found that fitness in early adulthood was not related to the presence or extent of coronary artery calcium 25 years later.

This doesn’t mean that exercise and being fit doesn’t reduce your risk of heart disease — in fact, we found that markers of heart muscle health were certainly improved with greater fitness. It does, however, suggest that the biological relationship between exercise and heart health is complex, and needs further study.

"The surprise in this study was that there was not a relationship of outcomes to coronary calcium scores," said Dr. Ira Ockene of UMass Medical School, who co-wrote a commentary on the study. "So what's that all about? Well, the authors didn't really know. But they raised a number of possibilities. One possibility is that in young people, disease has a different mechanism than you might see in older people," and the effects in arteries may progress at a different rate.

There's a great deal we don't understand about the biology that underpins the health benefits of exercise. But clearly, Dr. Ockene said, "We're designed to be very physically active, and when we just sit, it's not good."

Safety note: If you're a quantified-self health hacker and now want to use the study's calculations to assess your own heart-disease risk, Drs. Shah and Murthy caution against trying a treadmill test protocol at home or at the gym.

"We absolutely do not think that's a good idea," Dr. Murthy said. "These protocols are designed to wear people out very, very quickly; they're done under medical supervision. And what we really wouldn't say is a good idea is for people to go home and do this without that level of experience, because not only can they have heart complications, but they can have falls and injure joints. These are done with a whole medical team observing and supervising."

"That being said," he added, "People who feel like they're not currently exercising and don't feel like they're fit, absolutely it's a good idea to start an exercise program. But if you're not actively engaged in exercise and you're not in shape, it's also probably a good idea to see your doctor first."

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