Exercise in the prevention of cancer

Cancer is a word, not a sentence

Cancer and exercise

Cancers form a very large group of conditions that are extremely common causes of disease, disability, suffering and death. Nearly 40 per cent (% hereafter) of people will be diagnosed with one or another type of cancer in their lifetime and cancer causes nearly 30% of all deaths in the UK. Cancers are also very disparate, varying from minor skin excrescences to devastatingly fast-spreading and fatal malignancies. The place of exercise in the prevention and management of such a wide spread of conditions is likewise very variable.

The study and application of exercise, particularly in management of cancer, has now acquired its own label -“exercise oncology”. This is my subject for the next three blogs.

1. Prevention

Exercise and prevention
A number of studies suggest that regular exercise and high levels of physical fitness can reduce the risk of developing a number of different cancer types. Those involved include colon, breast, uterus, gullet, gall bladder, pancreas and kidney. The level of protection provided by regular exercise and the amount of exercise required to provide that protection varies with the cancer type.  For instance, physically active women have about a 20–30% reduction in risk of breast cancer, compared with inactive women. Physically active men and women have about a 30–40% reduction in the risk of developing colon cancer compared with inactive persons.  Endometrial (the lining of the womb) cancer is also less common in physically active women by a factor of about 20%. For most cancers there is a dose-response relationship, with higher levels of exercise giving higher levels of protection (see below).

The good news for those who work hard all week and have to cram their exercise into Saturdays and Sundays, so called “weekend warriors”, the benefits still apply. One study followed nearly 100,000 people for eight years after having their physical activity levels measured. The more active group were 21% less likely to have died from cancer than the inactive.

Scientists at Harvard Medical School looked at 136,000 health records and calculated that all cases of cancer would fall by 20-40% and deaths would drop by a half if everyone adopted a healthy lifestyle. This goes beyond just exercise and includes giving up smoking, losing weight and consuming low levels of alcohol. Unfortunately few people follow all the lifestyle advice, but if they did, deaths from lung cancer would drop by 80%, bowel cancer by up to 30%, prostate cancer by 21% and breast cancer by 12%.

The best current estimate is that around five per cent of all cancers in the UK may be related to physical inactivity. Physical inactivity is defined in this case as below a modest aspiration of 30 minutes five times per week, meaning that around 3,400 cases of cancer every year are linked to people doing less physical activity than recommended in government guidelines. With higher levels of activity it is likely that many more cases could be prevented.

Physical fitness and prevention
As might be expected, there is also a relationship between cardiorespiratory fitness (CRF) and cancer risk. A low level of CRF has been found to increase cancer risk by up to 50 per cent. It has an even greater effect on cancer mortality, reducing survival time free from cancer by as much as seven years. One meta-analysis found that individuals with a high CRF had a 45% reduction in overall cancer mortality compared with their unfit counterparts. Even more convincing was the finding that there was a dose response relationship between physical fitness and cancer mortality – that is, the effect of increased CRF is related to the level of that increase. In this case, for every increase of one MET (metabolic equivalent – see blog “Exercise & Oxygen”, published on 25th January, 2020, which explains METs as a measure of CRF)  there was a 14% reduction in cancer mortality.

Mechanism of prevention
It is not exactly clear why exercise prevents some cancers, but there are several possibilities. These include reduction of inflammation, a potent cause of a number of conditions, and improved immune function with higher levels of natural antioxidants. Body weight is also a big factor particularly in breast cancer which is linked to obesity. The International Agency for Research in Cancer claims that 25-30% of breast cancer cases could be avoided if women were thinner and exercised more. On the basis of recent estimates, the obesity-related contribution to cancer represents up to 9% of the cancer burden among women in North America, Europe and the Middle East.

Next time

The next episode will look at preparing the cancer patient for treatment – known as prehabilitation.