How Does Physical Activity Reduce Cancer Risk?

The short answer

Regular physical activity reduces the risk of at least 13 types of cancer, including colon (24% reduction), breast (12–21%), endometrial (20–30%), bladder (15%), kidney (12%), gastric (17%), and oesophageal (21%) cancers. The mechanisms include reduced insulin and IGF-1 levels, lower sex hormone concentrations, reduced inflammation, improved immune surveillance, and faster gastrointestinal transit time.

What the evidence actually shows

A landmark 2016 meta-analysis by Moore et al. in JAMA Internal Medicine, pooling data from 1.44 million adults across 12 cohort studies, found that higher leisure-time physical activity was associated with lower risks of 13 of 26 cancer types studied. The strongest associations were for oesophageal adenocarcinoma (42% reduction), liver cancer (27%), lung cancer (26%), kidney cancer (23%), gastric cardia cancer (22%), endometrial cancer (21%), myeloid leukaemia (20%), myeloma (17%), colon cancer (16%), head and neck cancer (15%), rectal cancer (13%), bladder cancer (13%), and breast cancer (10%). Friedenreich et al. (2010) estimated that 9–19% of colon cancers and 10–24% of breast cancers in the US are attributable to physical inactivity.

"Higher leisure-time physical activity was associated with lower risks of 13 cancer types, with reductions ranging from 10% to 42%."

— Moore et al., JAMA Internal Medicine 2016

What the major health authorities say

The NIH National Cancer Institute identifies physical activity as a cancer prevention strategy with strong evidence, noting that physically active people have lower risks of several cancers. The NIA recommends regular physical activity as a component of healthy ageing that reduces cancer risk. The American Cancer Society recommends at least 150–300 minutes of moderate-intensity or 75–150 minutes of vigorous-intensity activity per week for cancer prevention.

Practical implications

For cancer prevention, the dose-response relationship suggests that more activity provides greater benefit, with the strongest reductions seen at vigorous activity levels. However, even moderate activity (brisk walking, cycling) provides meaningful cancer risk reduction. The mechanisms differ by cancer type: for colon cancer, faster gastrointestinal transit reduces exposure of the colon mucosa to carcinogens; for breast and endometrial cancer, reduced oestrogen levels are the primary mechanism; for all cancers, reduced insulin and IGF-1 signalling reduces cell proliferation.

Where reasonable people still disagree

• Whether the cancer risk reduction from physical activity is primarily attributable to exercise itself or to its effects on body weight and adiposity.
• The optimal type, intensity, and duration of exercise for cancer prevention — whether vigorous activity provides meaningfully greater benefit than moderate activity for all cancer types.
• Whether exercise during or after cancer treatment improves survival outcomes, beyond its well-established benefits for quality of life and treatment tolerance.