Cardiorespiratory fitness may significantly lower the risks

Researchers used linked Swedish registry data up to the end of 2019 that included background information, medical diagnoses, and deaths for more than 1 million conscripts who started their military service between 1968 and 2005.

The subjects began their service when they were between 16 and 25 years old. They underwent a standard battery of assessments, including height, weight, blood pressure, muscular strength, and cardiorespiratory fitness.

Researchers looked at 365,874 conscripts with a low level of cardiorespiratory fitness as well as 519,652 with a moderate level and 340,952 with a high level.

Conscripts considered to have lower cardiorespiratory fitness were slightly more likely to be obese, more likely to deal with alcohol and substance misuse, and to have parents with lower educational attainment than the conscripts with a higher fitness level, the researchers reported.

In the final analysis of 1,078,000 men, researchers reported that 84,117 (7%) subsequently developed cancer in at least one part of their body during the average monitoring period of 33 years.

Compared with men having a lower level of fitness at conscription, ones with higher cardiorespiratory fitness were linearly associated with a lower risk of developing specific types of cancer.

Better cardiorespiratory fitness was associated with a:

• 5% lower risk of rectal cancer
• 12% lower risk of pancreatic cancer
• 18% lower risk of bowel cancer
• 19% lower risk of head and neck cancer
• 20% lower risk of kidney cancer
• 21% lower risk of stomach cancer
• 39% lower risk of food pipe cancer
• 40% lower risk of liver cancer
• 42% lower risk of lung cancer

Researchers also found higher cardiorespiratory fitness was also associated with a 7% heightened risk of prostate cancer and a 31% heightened risk of skin cancer.

The authors said prostate cancer screening and exposure to sunlight might account for these findings.

The research team said it’s an observational study, so no firm conclusions can be drawn about cause and effect. They also acknowledged they didn’t have full data on other potentially influential lifestyle risk factors, such as diet, alcohol intake, and smoking. Nor were they able to track any changes in cardiorespiratory fitness over time or gather any genetic information on participants.

The researchers did say that their findings are reflected in the American Society of Clinical Oncology guidelines on exercise during cancer treatment.

Dr. Anton Bilchik is a surgical oncologist, chief of medicine, and director of the Gastrointestinal and Hepatobiliary Program at Saint John’s Cancer Institute at Providence Saint John’s Health Center in California.

Bilchik told Medical News Today the results of the study could show that keeping cancer at bay could be about both having a healthier body and, specifically, how cardiovascular exercise can help fight off cancer

“Cardiovascular exercise induces an anti-inflammatory response which has been shown to stimulate the immune system thereby reducing the chance of getting both cardiovascular disease and cancer,” Bilchik said. “There are many factors associated with cancer reduction other than exercise including diet, lifestyle, alcohol use, smoking, and family history. Regular consumption of processed food and red meat is more often associated with colorectal malignancies while smoking is more often associated with lung cancer.”

Dr. Melinda Irwin, the co-leader of the Cancer Prevention and Control Research Program at the Yale Cancer Center in Connecticut, told Medical News Today the benefits of exercise are not about body weight.

“CRF (cardiorespiratory fitness) has direct benefits for cancer prevention, e.g., improved metabolic, inflammatory, and immune function that likely mediate the association between CRF and cancer risk,” Irwin said. “This study found that a higher CRF, while statistically controlling for BMI, was associated with lower cancer risk.”

“Moderate and vigorous intensity exercise is necessary to increase CRF,” she added. “Randomized trials have reported that 2.5 hours per week of brisk walking (i.e., a moderate-intensity physical activity) can lead to a 5 to 10 percent increase in CRF, with vigorous-intensity exercise (e.g., jogging) increasing CRF even more.”

Dr. Briana Costello, an interventional and general cardiologist at the Texas Heart Institute Center for Cardiovascular Care, said previous exercise may also be a factor in cancer risks.

“This could be a ‘what came first, the chicken or the egg’ question,” Costello told Medical News Today. “Those with underlying lung conditions and higher baseline lung cancer risk and decreased lung capacity may have worked out less.”

Costello noted that the higher rates of skin cancer of those with better cardiovascular health could be explained by being outside exercising.

“I imagine the skin cancer can be explained by sunlight exposure,” he said. “These types of studies do not allow us to draw conclusions about causality and further studies are needed.”

Los Angeles intervention cardiologist Dr. Vicken Zeitjian told Medical News Today the higher rates of prostate cancer could be an “outlier.”

Zeitjian agreed that the study shows people need to exercise to help fight off cancer

“Everyone should try to exercise with a gradual increase in duration and intensity,” Zeitjian said “The American Heart Association recommends 30 minutes of moderate intensity exercise at least 5 days per week and I encourage all my patients to build up to that.”

“Common reasons I hear for lack of exercise include ‘I have no time’ or ‘gym memberships are too expensive.’ I generally respond by explaining that a neighborhood jog, doing push-ups, sit-ups, doing plyometrics, and doing body weight exercises can be sufficient,” Zeitjian said. “Those are ways I typically exercise.”