A study that followed 170,000 Swedish men (average age 62) for 9.6 years found that high levels of physical fitness were associated with a markedly reduced risk for lung cancer or colon cancer, and reduced risk for death from cancers of the colon, lung or prostate (JAMA Netw Open, June 29, 2023;6(6):e2321102), Physical fitness was measured by having the subjects exercise vigorously on a stationary bicycle to determine the maximal amount of oxygen they could use (VO2max).

High levels of fitness were not associated with reduced risk for incidence of prostate cancer, possibly because men who are regular exercisers may be more likely to attend prostate cancer screening programs, so they are more likely to be diagnosed with prostate cancer. Most men live for many years after being diagnosed with prostate cancer.

How Level of Physical Fitness Can Affect Cancer Risk
A report in the British Medical Bulletin, “Why exercise has a crucial role in cancer prevention, risk reduction and improved outcomes” is the best article I have seen on the many ways exercise can reduce risk for cancers and for deaths from cancers (BMB, September 2021;139(1):100–119). The authors’ list of the benefits of a regular exercise program includes:
• helping to prevent high rises in insulin that cause cancer cells to grow (Cancer Causes and Control, 2011; 22(6):811-826)
• reducing cancer-stimulating hormones (Obes Rev, 2015;16:473–87)
• reducing inflammation that is a primary driver of cancer (J Am Geriatr Soc, 2008;56:2045–52)
• strengthening the immune system to help control cancer (J Am Geriatr Soc, 2008;56:2045–52)
• altering the metabolism of bile acids that increase cancer risk (Cancer Epidemiology, Biomarkers & Prevention, 2009; 18(5):1591-1598)
• decreasing exposure of the gastrointestinal tract to many carcinogens, since exercise moves food through your intestines faster (Mutation Research, 2005; 589(1):47-65)
• helping to control excess weight (J Clin Oncol, 2005;23:3830–42)
• reducing high leptin levels that are associated with increased cancer risk (Obes Rev, 2015;16:473–87)
• raising vitamin D levels (from outdoor exercise) that are associated with reduced cancer risk (J Clin Oncol, 2014;32:2430–9)
• reducing insulin-like-growth factor that is associated with increased cancer risk (J Natl Cancer Inst, 2000;92:1472–89)
• helping to promote tissue repair from damage from altered cancer cells (Breast Cancer Res Treat, 2009;115:213–20)
• increasing anti-oxidant enzymes to protect against environmental and oxidating carcinogens (Free Radic Biol Med, 2008;44:126–31)

My Recommendations
If you do not have a regular exercise program, check with your doctor to see if you have any conditions that might cause exercise to harm you. Then see my article on How to Start an Exercise Program. I hope that this will inspire you to start exercising so you are not willfully shortening your life.