Does exercise lower my risk of cancer?
More physical activity is consistently associated with a lower risk of most types of cancer. As few as 7,000 to 9,000 steps per day makes a measurable difference. Combine this with getting up regularly during the day and using good sun protection if you exercise outdoors a great deal.
Yes, exercise demonstrably lowers your risk of most types of cancer. An analysis of 1.44 million adults1 found that more leisure-time physical activity was associated with a lower risk of 13 types of cancer. The reduction ranged from 10% for breast cancer to 42% for oesophageal cancer. A separate analysis of 98 studies involving more than 16 million participants2 confirms this: for breast, colorectal, lung, stomach and liver cancer, the risk was 5 to 17% lower with more physical activity. For six types, including colon, uterine and bladder cancer, that association has been strongly confirmed on multiple occasions3,4.
You really do not need to exercise intensively to benefit. A study of 85,394 participants in which physical activity was measured objectively5 found that 7,000 to 9,000 steps per day was already associated with an 11 to 16% lower cancer risk compared with 5,000 steps. After that the effect levelled off; more steps produced no clear additional benefit. Even gentle walking or sitting a little less was already associated with a 6% lower risk. If you are currently inactive, there is therefore already something to gain from a small step up.
There is one important caveat. That same large analysis1 also found a higher risk of melanoma (27% higher) and prostate cancer (5% higher) among people who exercise a great deal. The higher melanoma risk is most likely due to greater sun exposure from outdoor sports. If you do a lot of outdoor exercise, use sun protection consistently.
Prolonged sitting carries a separate risk that you cannot fully eliminate by also exercising. Even if you are sufficiently active, your risk of colon, uterine and lung cancer may remain elevated if you spend the rest of the day predominantly sitting3,4,6. Getting up regularly and moving around throughout the day is a worthwhile addition to exercise, not a replacement for it.
Why does it work? Exercise lowers sex hormones such as oestrogen, improves how your body responds to insulin, reduces chronic low-grade inflammation and may have an effect on the immune system and gut microbiome3,7,6. These explanations are biologically plausible. All available data are observational, however: a direct causal relationship is plausible but has not yet been proven in large-scale randomised trials.
All claims are drawn from large observational studies and systematic analyses involving up to 16 million participants. There are no randomised controlled trials testing cancer as an endpoint. Causality is plausible but not proven. One direct meta-analysis used as a source: PMID 37743572, a systematic analysis of 98 studies.