Links between cancer and physical activity

Epidemiological evidence:

A recent study investigating the extent of cancer burden attributed to physical inactivity in Australia in 2015 found that 11.9% of cancer cases occurring across 13 different cancer sites could be linked to suboptimal physical activity levels.¹ It was proposed that even a modest increase in physical activity a decade earlier could have prevented 4.8% cases of cancer at the 13 sites.¹

A combined analysis of studies from the US, Europe, and Australia, published in 2020, demonstrated that engagement in the recommended amount of activity (150 minutes of moderate-intensity physical activity or 75 minutes of vigorous-intensity physical activity per week) was associated with a statistically significant lower risk of 7 out of the 15 studied cancer types, including colon, breast, endometrial, kidney, myeloma, liver, and non-Hodgkin lymphoma.² Similarly, benefits have been observed among people living with metastatic breast cancer. A recent study found that two hours of supervised exercise per week offers significant benefits to people with metastatic breast cancer including improvements to quality of life and decreased healthcare costs.³

Prolonged sedentary behaviour has been found to be associated with an elevated susceptibility to developing cancer.⁴ Multiple studies have demonstrated that individuals who engage in long periods of sedentary behaviour have a significantly higher risk of developing colon and endometrial cancer compared to those who engage in less sedentary habits.⁵ This prolonged sitting behaviour is further correlated with higher risk of breast, ovarian, and prostate cancers, and it can also lead to an increased likelihood of cancer-related deaths in women.^4,6

Body composition

Physical activity may reduce adiposity. Adiposity may contribute to cancer risk through increased levels of sex and metabolic hormones, chronic inflammation and altered secretion of adipokines.¹ Adiposity has been linked to the development of 13 types of cancers including oesophagus, liver, colon, breast, and endometrial cancer.^2,3

Metabolic function

Elevated insulin levels have been directly linked to an increased risk of some cancers because they possess characteristics that encourage cell growth and stimulate growth signals, including the activation of the Insulin-like growth factor (IGF-1) system, which is involved in cell development, growth, and cell death.^1,4,5 Physical inactivity can increase cancer risk by decreasing insulin sensitivity, increasing insulin and glucose levels as well as activating the IGF-1 system.⁵

Inflammation

Inflammation has been associated with the development of numerous cancer types primarily due to its potential to stimulate cell growth, alter the body's internal environment, and induce oxidative stress. Adipokines, which are inflammatory molecules released from body fat tissues, are implicated in insulin resistance, both of which have been linked to colorectal cancer development.⁴ Physical activity, on the other hand, has been shown to modify the immune system, bolstering both innate and acquired immunity and supporting the body's ability to monitor and combat tumours.

Sex hormones

Physical activity has been linked to lowering levels of oestrogen and growth factors which have been linked to the development of breast and endometrial cancer.⁵ Sex hormone binding globulin can also affect cancer risk by binding to the oestrogen and androgens making them inactive.⁵