The diagnosis of cancer is a shock to patients. In a DW interview, Professor Wilhelm Bloch from the German Sport University in Cologne explains what influence sport can have on cancer treatment.

Mr Bloch, in which area do you and your colleagues at the Institute for Circulatory Research and Sports Medicine conduct research on cancer?

Professor Wilhelm Bloch: Four out of ten working groups here at the institute deal with the topic of sports and cancer. We are currently working on a large EU project, which is about new therapy applications with highly intensive interval training for women with breast cancer. We want to work out new approaches: What actually happens in the body of a cancer patient when he does sports? We are investigating whether the sport has an effect and possibly also supports therapy. In the past few years, this has increasingly come into focus.

What was the approach in previous years?

When we started research in 2007, the main focus was on the side effects that can result from a tumour or therapy, and their possible reduction. Over time, however, it turned out that physical activity is and can be more than just an aid to side effects. 

In what way?

On the one hand, the preventive character: the sportsperson does something to ensure that he is not at so high a risk of getting cancer. On the other hand, we recognize that exercise in rehabilitation helps to overcome cancer. There is currently an increasing focus on using sport to accompany therapy to enhance the effects of therapy.

What processes take place in the body when a cancer patient does sports?

Sports trigger processes that help fight the tumour. Exercise doesn’t cure cancer. But you put the body in a position to cope better with cancer or to process therapy better. A key mechanism is to stimulate the immune system. Every physical activity triggers something like stress on the immune system, which reacts to it and changes its parameters and its activity. Immunological processes occur that have a direct impact on cancer.

How does that concrete look?

Professor Wilhelm Bloch has been researching the interaction of sport and cancer for twelve years (DSHS Cologne)Professor Wilhelm Bloch has been researching sports and cancer for twelve years

An example that we have researched here is the natural killer cells. These recognize tumour cells, attack them and can also destroy them. We call this lytic activity. This means how many tumour cells are dissolved by the natural killer cells. However, these killer cells can be “sharp” in different ways. The activity in these cells increases during exercise and after exercise. There are also many other cells that play a role in cancer and that react similarly. 

How active are these killer cells?

We can assume that our body is flooded with a lot of degenerate cells every day. Fortunately, the body copes well with it. But at some point, there is a point where this no longer works and a nest of tumour cells settles somewhere. It can sleep for many years, and suddenly the tumour begins to grow. We have this threat at all times. If you have certain physical tendencies or genetic changes, you cannot prevent that with exercise. Skin cancer is an example of this. But sport can help slow down small events. Then I gained a lot as a patient. We speak of probabilities: What percentage do I reduce my risk?   

What should an exercise look like to prevent cancer?

If you walk or walk moderately for six hours a week, I reduce my colorectal cancer risk by 40 per cent. For prostate carcinomas, the value of the risk reduction is around 25 to 30 per cent. So also with breast cancer. Especially with colon cancer, I can get very good protection through good nutrition. If I am overweight, my risk of cancer increases. 

Are there any types of cancer where sports don’t help?

There are a few, such as rectal carcinomas. No effects can be demonstrated with them. There are only minor effects in lung carcinomas. But if you smoke, the effect on the development of a tumour is much greater than you could make up for it with exercise. Basically, however, it can be said that almost every tumour can be prevented with physical activity. 

How does sport support cancer therapy?

Stimulating the immune system has an advantage. If I do sports correctly and dose correctly, it also improves the general condition of the patients. A patient can endure more therapy when he is fitter. A patient who is not fit may discontinue chemotherapy that is important to him because he simply cannot tolerate it physically. This increases the risk that the therapy will not work. We now assume that it is almost a must to think about sports and exercise therapy for cancer patients.

Strength training should be used during cancer therapy (picture-alliance / Marco Wolf)Strength training should be used during cancer therapy

So more sport is much better?

If I keep the patient fit at the same time, he will be able to continue the therapy longer or with a higher dosage. Sometimes competitive athletes tolerate very high doses that could not be given to a “normal” person. It is a special situation that the patient survives this at all.

What type of sport is recommended in cancer therapy: endurance or strength training?

The most difficult question is how exactly I have to control the training. We are not yet so far in research that we can say that exactly. In the past, we would have advised patients to undertake gentle, moderate, more endurance-based training. Today, patients can also do highly intensive interval training – if they use it correctly. In the meantime, we combine strength and endurance sports and also sprinkle highly intensive units. We have to build muscles that the patient loses during therapy. Sport can be used like a kind of medicine. I would also see sport as a medicine.

Professor Wilhelm Bloch heads the Institute for Circulatory Research and Sports Medicine at the German Sport University Cologne and conducts research in the field of molecular and cellular sports medicine. Bloch’s research focuses on the medical and cell biological adaptation of tissues and organs to physical stress. He also looks at the impact of exercise on cancer patients.

The interview was conducted by Jörg Strohschein.


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