Physical activity and cancer risk

Regular physical activity is associated with reduced risk of several cancer types, and the evidence base has grown substantially over the past two decades. The cancers with the strongest evidence for a protective association include colorectal cancer, post-menopausal breast cancer, endometrial cancer, kidney cancer, and bladder cancer. Physical activity is also relevant to cancer survivorship, where it may reduce recurrence risk and improve quality of life, and in the prehabilitation context before cancer surgery.

Multiple biological mechanisms have been proposed to explain how physical activity may reduce cancer risk. Regular exercise reduces circulating insulin and IGF-1 levels, hormones that promote cell proliferation. It reduces excess body fat, particularly abdominal adiposity, which is itself a cancer risk factor through inflammatory and hormonal mechanisms. Exercise enhances immune function, including natural killer cell activity and cytotoxic T lymphocyte surveillance, which may improve recognition and elimination of early transformed cells. Physical activity reduces intestinal transit time, potentially limiting mucosal exposure to dietary carcinogens in the colon. Elevated sex hormone binding globulin (SHBG) with physical training reduces the bioavailability of oestrogen and testosterone, potentially reducing the hormonal drive in hormone-sensitive cancers. In animal models of prostate cancer, exercise has been shown to reduce tumour progression and influence oxidative stress response pathways through mechanisms distinct from those of anti-inflammatory pharmacological agents.

The European Code Against Cancer 5th edition identifies physical inactivity and prolonged sedentary behaviour as widespread and important modifiable cancer risk factors, and recommends regular exercise as a component of cancer prevention. A narrative review of lifestyle-based cancer prevention found that physical activity is consistently associated with reduced risk for colorectal, breast, and endometrial cancers, and that it improves treatment tolerance and survivorship outcomes. A systematic review and meta-analysis examining exercise and cancer-related lymphoedema found that exercise does not increase and may in fact reduce lymphoedema incidence, contradicting earlier clinical caution that had limited exercise recommendations for at-risk patients. Multimodal prehabilitation programmes combining physical activity with nutritional support have shown feasibility and early efficacy signals in digestive oncology, where improved preoperative fitness may reduce postoperative complications and accelerate recovery. In breast cancer survivors, maintaining 24-hour movement behaviours including adequate physical activity and restorative sleep was associated with better quality of life outcomes over time.

People who are physically inactive or sedentary for most of the day are at the greatest risk from this modifiable factor. Women with a sedentary lifestyle face elevated endometrial and post-menopausal breast cancer risk. Cancer prevention benefit appears to accumulate with increasing activity volume, but even modest increases from very low baselines appear to confer some benefit across most studies. People with excess weight or metabolic syndrome who become more physically active may simultaneously reduce multiple cancer risk factors including adiposity, insulin resistance, and chronic inflammation.

Evidence is mostly observational, from large prospective cohort studies and case-control studies. Randomised controlled trials are limited because randomising people to long-term physical activity interventions with cancer incidence as a primary endpoint is logistically difficult. The association is consistent across the cancer types where evidence is strongest, dose-response relationships have been described, and the biological mechanisms are plausible and partially characterised. Major cancer prevention bodies, including the European Code Against Cancer and the World Cancer Research Fund, have incorporated physical activity recommendations into cancer prevention guidance.

Studies consistently suggest that regular physical activity is associated with reduced risk for several cancer types, particularly colorectal, breast, and endometrial cancers. Physical activity also appears to benefit people during and after cancer treatment by reducing complications such as lymphoedema and improving quality of life and functional recovery. There is no evidence that appropriate levels of exercise increase cancer risk in healthy individuals.