Exercise helps keep your hormone levels healthy and your immune system robust, which are both great cancer defense mechanisms.
Getting your sweat on regularly is linked with a 24% lower risk of colon cancer, 12% lower risk of breast cancer in women, and a 20% lower risk of uterus cancer, when cancer rates in regular exercisers are compared to couch potatoes.
Specifically, women who work out can lower their estrogen levels. That helps reduce cancer risk, since too much estrogen can encourage breast cells to divide more frequently. Likewise, staying active can keep insulin levels in the body in check, which also helps lower one's chances of getting cancer.
A 2016 study of more than 1.4 million people in the US and Europe found that people who exercised regularly cut their risk of developing 13 different kinds of cancer. People who worked out the most (the top 10% of exercisers) had a 20% lower risk of developing those cancers (esophageal adenocarcinoma, liver, lung, kidney, gastric cardia, endometrium, and myeloid leukemia) than the bottom 10% of exercisers the group.
Regular movement also helps you digest your food more quickly and can reduce inflammation in the gut, which means that any potentially cancer-causing compounds you've ingested will spend less time in your body and have fewer chances to wreak havoc on your cells.