A new study adds to the large body of evidence that being in good physical shape can dramatically reduce cancer risk.
The study, published Tuesday in the British Journal of Sports Medicine, found that men with high levels of cardiorespiratory fitness in young adulthood had a lower risk of developing nine forms of cancer years later, including in the head and the neck, the lungs, the kidneys and the gastrointestinal system.
The study followed more than 1 million young men in Sweden over an average of 33 years, starting when they took a military fitness test that, until 2010, was legally required at around 18 years old. The researchers then analyzed the rates of cancer diagnoses among the men and compared them to the fitness levels registered on their military tests.
The test involved riding a stationary bike, first at a low resistance level for five minutes, then with an increase in resistance of 25 watts per minute until the test takers were too tired to continue.
The authors of the new study sorted participants into low, moderate and high levels of cardiorespiratory fitness — a measure of how well one’s cardiovascular and respiratory systems supply oxygen to the muscles — based on their bike test results. They found that the people with high fitness levels had a 19% lower risk of head and neck cancer and a 20% lower risk of kidney cancer compared to the low-fitness group.
The risk of lung cancer, meanwhile, was 42% lower for the fittest participants, though that was explained mainly by people’s smoking habits.
The lead author of the study, Dr. Aron Onerup, a postdoctoral researcher in the pediatrics department at the University of Gothenburg in Sweden, said the risk of cancer generally continued to decrease as participants’ fitness levels increased.
“But you don’t have to reach the top, elite athlete level to have a lower risk,” he said. “An increase in fitness seems to be associated with a lower risk of developing most of these cancers.”
Onerup said he was particularly surprised by the findings about gastrointestinal cancers: The study showed that the risk for high-fitness participants was nearly 40% lower for cancers in the esophagus, the liver, the bile ducts and the gallbladder and about 20% lower for the stomach and the colon.
Rates of gastrointestinal cancer among young people have surged in recent decades. In March, the American Cancer Society reported that people under 55 accounted for 20% of all colorectal cancer cases in the U.S. in 2019 — almost double the 11% they accounted for in 1995. A 2021 study estimated that within seven years, colorectal cancer could rank as the leading cause of cancer deaths in the U.S. among people ages 20 to 49.
“From a public health perspective, you can see the kind of risk reductions that you might be able to achieve if you put public health efforts into facilitating physical activity and fitness in the population,” Onerup said.
Dr. Kathryn Schmitz, a professor of hematology and oncology at the University of Pittsburgh who was not involved with the new research, said the study adds to a “robust lexicon” of research linking physical activity to a lower risk of many common cancers.
Indeed, a March study involving more than 30 million participants found that just 11 minutes of daily physical activity was linked to lower risk of death from various cancers. And a 2016 analysis found that higher physical activity levels were associated with a reduced risk of developing 13 of 26 cancers studied. Studies have shown that physical activity is linked to a 30% lower risk of death even after colorectal cancer diagnoses, according to the National Cancer Institute.
Schmitz said the new study is especially valuable because it relied on a standard baseline assessment of fitness, rather than ask participants to self-report their exercise regimens.
“There’s an inflation of what we actually do when we record our own physical activity, and you can’t do that with fitness,” Schmitz said. “So it’s a better reflection of what the person is actually doing on a regular basis.”
Contrary to the study’s main findings, the data showed an association between high fitness levels and an increased risk of two types of cancer: melanoma and prostate cancer. Onerup and Schmitz both thought that was most likely because people with higher fitness levels are more likely to be exposed to the sun and more likely to get screened for prostate cancer.
Schmitz pointed out a couple of key limitations of the study: For one, it did not include women. Second, the participants’ lifestyle factors or subsequent fitness levels were not assessed after the initial tests, leaving questions about other mitigating factors that might have affected the cancer rates.
However, the study does shed light on how physical fitness at a young age can affect health later in life, Schmitz said.
“This does point us in the direction of wanting to have a higher amount of physical activity in our youth,” she said.
