Exercise and movement
Physical activity is defined as any movement that uses skeletal muscles and requires more energy than resting. Physical activity has an effect on several bodily systems including endocrinologic, immunologic and metabolic processes which can, in turn, affect the risk for development of several cancers. Being physically active also helps to maintain a healthy weight and protect against cancer.
New technologies have encouraged people to increase the time they spend engaging in sedentary behaviours such as sitting in cars and watching television as well as using computers, electronic entertainment and mobile phones. The World Health Organization estimates that in 2010, globally about 23 per cent of adults did less than the recommended level of activity of at least 150 minutes of moderate-intensity aerobic physical activity per week. The proportion of adults in high-income countries not meeting the recommended levels of activity is higher.
Insufficient levels of physical activity have been linked to a number of health problems including cardiovascular disease, stroke, diabetes, obesity, poor bone health and depression.
OUR MAJOR FINDINGS ON CANCER AND PHYSICAL ACTIVITY
There is strong evidence that:
being physically active DECREASES the risk of
vigorous physical activity (eg running or fast cycling) DECREASES the risk of
- pre and postmenopausal breast cancer
The evidence implies that, in general, the more physically active people are, the lower the risk of some cancers.
– This is the opinion of the Expert Panel and forms the basis of our Recommendation on physical activity
Physical activity and colorectal cancer
Physical activity reduces body fatness and therefore has a beneficial effect on colorectal cancer risk, possibly through a reduction in insulin resistance and inflammation – both of which have been linked to colorectal cancer development. However, it is unclear whether physical activity that is not accompanied by weight loss or maintenance of a healthy weight has a significant impact on these pathways. Other mechanisms by which physical activity may lower colorectal cancer risk include stimulating digestion and reducing transit time through the intestine, though robust data to support this mechanism in humans is limited.
Physical activity and postmenopausal breast cancer
Physical activity affects a diverse array of metabolic, hormonal, and immunologic pathways. Regular physical activity reduces body fatness and therefore has a beneficial effect on breast cancer risk, possibly through a reduction in circulating oestrogen levels, insulin resistance and inflammation – all of which have been linked to postmenopausal breast cancer development. However, it is unclear whether physical activity that is not accompanied by weight loss has a significant impact on these pathways.
Physical activity improves insulin sensitivity and reduces fasting insulin levels, which are linked to higher breast cancer risk in humans. Exercise may also affect breast cancer risk through its effects on insulin-like growth factors (IGFs), because high levels of circulating IGF-1 are associated with increased risk of several cancers, including breast cancer. In addition, physical activity has been shown to have immunomodulatory effects in humans, improving innate and acquired immune response, and promoting tumour surveillance.
Studies have also shown that aerobic exercise can decrease oxidative stress and enhance DNA repair mechanisms in humans and would therefore be expected to suppress carcinogenesis. Physically active individuals also tend to have higher sunlight exposure and consequently higher levels of vitamin D, which may modify cell proliferation.
Physical activity and premenopausal breast cancer
Human epidemiologic studies have shown that greater exposure to oestrogens increases the risk of breast cancer in both premenopausal and postmenopausal women. Physical activity has been shown to decrease levels of oestrogens and androgens in postmenopausal women, and some trials have also shown reductions in circulating oestrogens, increased menstrual cycle length, and decreased ovulation in premenopausal women with a high level of physical activity.
Physical activity and endometrial cancer
Physical activity reduces body fatness and therefore has a beneficial effect on endometrial cancer risk, possibly through a reduction in circulating oestrogen levels, insulin resistance and inflammation – all of which have been linked to endometrial cancer development. Physical activity has been shown to decrease oestradiol levels, improve insulin sensitivity and reduce chronic inflammation – all pathways which have been linked to endometrial cancer development.
Limited evidence on other cancers
There is also other evidence on physical activity that is limited (either in amount or by methodological flaws), but is suggestive of a decreased risk of oesophageal, lung and liver cancers. In addition, there is evidence on sedentary behaviours that is limited but is suggestive of an increased risk of endometrial cancer. Further research is required, and the Panel has not used this evidence to make recommendations.
> Read more about the cancer process