What a cardiac stress test can reveal about your risk of cancer

You can’t blame Jack Merendino for being nervous when he stepped on the treadmill for an exercise stress test last year. Just a few months earlier his younger brother had major heart surgery, both his parents died of heart disease, and his cardiac calcium score—which reflects calcium deposits and plaques clogging his arteries—was slightly elevated. More alarming: a week earlier he’d felt chest pain.

“I braced myself for a diagnosis of heart disease—or at least to be told I’m out of shape,” says Merendino, now age 64, and an endocrinologist practicing in Bethesda, Maryland. Much to his relief, his overall score—which factored in heart rate, blood pressure and other measures—was in the top five percent of men his age. That means it’s unlikely he has heart disease. What the test revealed that he didn’t know before: he might be at lower-than-average risk of cancer.

That’s according to recently published results from Minnesota’s Mayo Clinic, showing a strong association between the outcome of a stress test, typically used to diagnose heart issues, and future cancer risk.

In the Mayo study, researchers tracked 13,382 men and women from Minnesota who took a 10–15-minute treadmill stress test between the years 1993 and 2010. After starting slow, a person gradually works up to exercising as hard as possible. Meanwhile, blood pressure, aerobic fitness, heart rhythms, and heart rate are measured. The researchers followed up on participants about 13 years after their stress tests, checking blood pressure and other measurements against risk of death. They also calculated an “exercise score” by plugging in values for each measurement into an equation.

“The interesting finding was that the risk of dying from non-cardiovascular diseases was more than double for people who did the worst on the test compared to those who did the best,” says senior author Thomas G. Allison, a professor of medicine at Mayo Clinic Alix School of Medicine in Rochester, Minnesota. Those “non-cardiovascular diseases” are 14 causes of death that include dementia, stroke, and pneumonia. But the biggie was cancer, comprising half of all non-cardiovascular deaths.

Why would a stress test—designed to help diagnose heart disease—predict deaths from cancer? “It makes sense to me,” says Emily Lau, a cardiologist and professor at Harvard Medical School, who was not involved in the Mayo stress test study, “because cardiovascular disease and certain types of cancer share some of the same risk factors.”

Cardiovascular risk mirrors cancer risk 

In research that dovetails with Allison’s new study, Lau and her team reviewed results from two separate studies tracking the health of 20,305 men and women who were 36 – 64 years old at study’s start. One took place in Framingham, Massachusetts (Framingham Heart Study), the other in Groningen, in the Netherlands (PREVEND study).

Instead of stress tests, the Framingham and PREVEND studies looked at many factors linked to cardiovascular disease such as blood cholesterol, body mass index (a rough indicator of body fat), and diabetes. They also used the ASCVD (atherosclerotic cardiovascular disease) questionnaire, which found that people in the highest cardiovascular risk category were not only more likely to develop heart disease, but 3.7 times more likely to develop cancer in the 15-year follow-up period than those at lowest risk.

Researchers also plugged-in metrics—blood cholesterol, exercise habits, and dietary patterns—from Framingham study participants into an American Heart Association’s “Life’s Simple 7” risk assessment tool. Like the ASCVD results, those with the lowest risk of cardiovascular disease were less likely to develop cancer.

The fitness—cancer link

There’s good reason Life’s Simple 7 includes exercise habits, down to the minutes per week; physical activity is solidly linked to heart health. While a stress test can’t tell your doctor how much exercise you get, it’s very good at measuring aerobic fitness. “And that has major implications for both cardiovascular risk and risk for certain cancers,” says Allison.

“Fitness” in the exercise science world is technically “functional aerobic capacity” or “aerobic fitness” or “cardiorespiratory fitness”; it’s the ability of your body to deliver oxygen to muscle cells as you exercise. “The stronger your heart and lungs, the more oxygen moves into cells, the greater your fitness level, and the more protected you are from heart disease and other cardiovascular conditions,” Allison explains.

A stress test measures fitness using “VO₂ Max”: The maximum volume of oxygen your body can take in as you’re exercising as hard as you can. Younger people, and males (because they have a higher percentage of muscle than females), have a higher VO₂ max. And most everyone can raise VO₂ max with regular aerobic exercise—walking, jogging, rowing, biking, or any other exercise that raises heart rate and makes you breathe harder.

Participants in the Mayo Clinic study with functional aerobic capacity just 10 percent lower than average were 68 percent more likely to die from a cardiovascular issue, and 42 percent more likely to die of other diseases, mainly cancer, than people with higher scores. And that’s just fitness! Plug functional aerobic capacity, blood pressure and other stress test measures into an overall “exercise score” and those with the worst scores were five times more likely to die from heart attacks, heart failure, and other cardiovascular issues than those with the best scores.

“Fit people are not only less likely to get cancer, they’re also more likely to survive it. They’re more apt to survive almost any disease, even falls and fractures. If you can get up and move around, you are more likely to make it home,” notes Allison.

You don’t have to be an athlete to reap benefits; just hitting the recommended 150 minutes of moderate intensity aerobic exercise is linked to a 23 to 40 percent reduced risk of cardiovascular disease compared to being sedentary. Likewise, being physically active is associated with an eight to 25 percent reduced risk of certain cancers—with breast, colon, endometrial, gastric and lung cancers at the upward end of that range. Meanwhile, you’re also helping to ward off obesity, type 2 diabetes, depression, and other chronic diseases.

Your workout, your gut, and cancer

Exercise works its magic by strengthening the heart muscle, while tamping down instigators of cardiovascular disease and cancer, such as obesity, inflammation, and high blood sugar.

Emerging research suggests that at least some benefits may start in the gut, the home of trillions of microorganisms. (Yep, another notch in the gut microbiome’s belt!)

“Our research indicates that exercise … ramps up levels of bacteria that produce short-chain fatty acids. These acids are protective against colorectal cancer,” according to Alexander Boytar, a PhD candidate at the School of Human Movement and Nutrition Sciences at The University of Queensland, Australia.

“They may even travel to other areas of the body and offer protection against other cancers,” Boytar wrote in an email. Physical activity also prompts intestinal cells to churn out more immune cells which tamp down inflammation—and the development of cancer.

These microbiome benefits may at least partly explain why exercisers are less likely to get certain types of cancer. The evidence is particularly strong when it comes to colorectal cancer—the third most commonly diagnosed type and second leading cause of cancer death globally. Physically active people have a 24 percent lower risk of developing this cancer than sedentary people.

“It’s not just cancer prevention—the gut microbiome may bolster the effectiveness of chemotherapy and immunotherapy, as well,” Boytar wrote.

How much exercise? “Thirty to 90 minutes of aerobic exercise, three or more times per week, for eight weeks is likely to tilt the balance of gut microbes in our favor,” Boytar wrote.

It’s not just exercise…

As powerful as exercise is, it’s not the end-all. “I suggest following the American Heart Association’s “Life’s Essential 8” which spells out specific recommendations not only for exercise, but for eating better and other healthy habits,” recommends Lau. In her research, she used the version available at the time called “Life’s Simple 7.” Since then, the American Heart Association added an eighth heart-protective habit—getting enough sleep. Still understudied, research is suggesting that sleep disturbances raise cancer risk by upsetting circadian rhythms and raising inflammation.

Jack Merendino is taking heed. “Even with decent stress results I’m not taking my heart health for granted. Before the test I frequently pulled all-nighters or got by on just five hours of sleep. I knew about the association between lack of sleep and heart disease, and now that I hear there might be a cancer link, I have another reason to turn the lights off earlier,” he says.