Cancers form a very large group of conditions which are extremely common causes of disease, disability, suffering and death. Nearly 40% 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 variety of conditions is likewise very diverse.
Exercise in the prevention of cancer
It has been known for many years that some cancers are more common in physically inactive people. Cancers involved include colon, breast, uterus, gullet, gall bladder, pancreas, kidney, lung, stomach, bladder and blood (ie leukemia)
The reduction in risk provided by exercise has been calculated for a number of different cancers:
Colon 30-40% lower
Endometrium (lining of the womb) 20% lower
Breast 20-30% lower
Gullet 42% lower
The amount of exercise needed to reduce cancer risk is generally in line with the Department of Health (DoH) recommendations – 150 minutes per week of moderate exertion plus muscle strengthening exercise on two days of the week. In some cancers, for instance colon and breast, there is a dose response effect – the more the exercise, the less the risk.
The World Cancer Research Fund in 2009 estimated that 12% of colon cancers, 12% of breast cancers and 30% of endometrial cancers in the UK are related to inadequate physical activity.
The role of obesity
Closely related to lack of exercise, overweight and obesity are among the commonest contributory causes of cancer. Exercise clearly has a preventive role here.
At least eleven different types of cancer are associated with obesity – gullet, multiple myeloma, stomach, colon, rectum, biliary system, pancreas, breast, uterus, ovary and kidney. In 2013, an estimated 4.5 million deaths worldwide were caused by overweight and obesity; On the basis of recent estimates, obesity-related cancer represents up to 9% of the cancer burden among women in North America, Europe, and the Middle East.
Losing weight may also have an an effect. In one study women who lost weight after age 50 and kept it off had a lower risk of breast cancer than women whose weight remained stable,
Reduction in incidence of lung cancer has been linked with higher levels of physical fitness. Regardless of smoking status, higher levels of cardiorespiratory fitness are associated with a lower incidence of lung cancer by around 30%. Mortality from lung cancer is about five times higher in the physically unfit.
In another study baseline cardiorespiratory fitness (treadmill exercise test) was assessed in 565 men aged 58.9 ± 17 with documented cardiovascular disease and free from any malignancy. Higher cardiorespiratory fitness was independently associated with lower risk of cancer mortality and with extended survival time.
The message is clear. Taking regular exercise and keeping physically fit are very effective ways of reducing the risk of developing cancer.
Next week I will talk about the use of exercise as a treatment for cancer patients.
The hunter/gatherer model
It is interesting to take an evolutionary view of the way we have used exercise to survive as a species. The physiology of human responses to exercise evolved to support our prehistoric physical activity imperatives – to hunt and gather our food and to avoid becoming part of the diet of other predators. This article1 proposes that the most efficient way of keeping fit is to follow a model of exercise which was necessary for the survival of our ancestors. Well worth a read.