Exercise seems to have an effect on cancer, no matter if you hike in the mountains, work our in the gym or clean your house. (Photo: Shutterstock)

Professor: Physical activity may prevent cancer risk

American researchers have given concrete estimates as to what extent physical activity is able to reduce the risk of breast and colon cancer. The goal is that doctors will one day prescribe physical activity to patients the same way as they do regular medication. However, Danish researchers are more hesitant.

What if you could prevent breast cancer by swimming two times per week?

What if you could reduce the risk of having a colon cancer setback by lifting weights 3 times 10 minutes every day?

This could be some of the recommendations to come from the work of the American researchers, which they are going to present in further detail this fall.

The ECSS Congress in Prague

In July, about 2,700 people, mostly scientists, from 80 countries attended a four-day congress on sport and physiology. The congress was organised by the European College of Sport Science (ECSS).

"Physical activity may reduce mortality by 30 percent"

Later this year, scientific articles will be making suggestions as to what extent different types of physical activity may prevent different types of cancer.

Their goal is to one day be able to make specific recommendations as to how to exercise in order to reduce the risk of cancer, cancer recurrence as well as dying from cancer diseases.

Considerable amounts of research exist on the link between cancer and exercise, whereas time has come to be more specific as well as having doctors take exercise as a healing agent seriously. This was the opinion presented by Professor Kathryn H. Schmitz at a congress in Prague, where Science Nordic was invited.

"I would like to bring your attention to breast, colon and prostate cancer. It appears physical activity reduces the risk of mortality by 30 percent or more, after diagnosis."

"We are not only talking about 1-2 studies. There continues to be more and more evidence", says Kathryn H. Schmitz, Professor at the Department of Health Sciences at Penn State University, at the ECSS Congress in Prague.

Exercise fights seven types of cancer

Kathryn H. Schmitz has published more than 200 scientific articles on subjects including exercise and cancer. Moreover, Schmitz is leading a working group at the American College of Sports Medicine (ACSM) that is going to introduce the aforementioned cancer recommendations this fall.

At the Congress, Kathryn H. Schmitz mentioned some specific numbers during her presentation. However, she asked them be held from the public until they have been peer reviewed in a scientific magazine.

Opposite effect on one type of cancer

According to Kathryn H. Schmitz, there is one exception to the otherwise positive effects on cancer: birthmark cancer. In the case of birthmark cancer, there seems to be even more cases in people who exercise.

A theory could be that people who exercise tend to spend more time outdoors, whereas they are more exposed to damaging UV rays.

She also mentioned seven types of cancer, which she believes could be prevented by being physically active:

  • Breast
  • Colon
  • Esophageal
  • Bladder
  • Kidney
  • Stomach
  • Uterus

Physical activity includes many different types of activities. It could be a sport or free time activity, it could be walking or cycling on the way to work, and it could be housecleaning. According to Kathryn H. Schmitz, 'ordinary housework' seems to be able to prevent cancer in breast, colon and uterus.

Physical activity prescribed as medication

The goal is to be able to instruct cancer patients how – and how little – they need to exercise in order to fight the particular type of cancer they are suffering from.

However, as early as this fall, they are planning to be making similar recommendations on how physical activity may fight the side effects of cancer treatment, such as anxiety or fatigue, which often follows radiation or chemotherapy.

"We have strong evidence that exercise helps anxiety, depression and fatigue. However, since cancer patients may have difficulties being physically active, we are trying to figure out the minimum amount of exercise possible. We would like to be able to prescribe physical activity the same way as we do medication", Kathryn H. Schmitz declared at the congress in Prague.

You can watch the entire session, including the professor’s presentation in this YouTube video posted by ECSS:

The session is presented by Danish professor Bente Klarlund Pedersen from TrygFonden's Centre for Physical Activity Research. (Video: ECSS)

When it comes to doctors being able to prescribe physical activity to fight cancer, Kathryn H. Schmitz mentions two possible pitfalls:

  • It is one thing being physically active when doing a scientific experiment. Real life is something else, especially when considering the ones who do not usually exercise.
  • Most experiments have been done on patients suffering from breast cancer. Therefore, the question is whether these results can be directly applied to other types of cancer. However, when introducing this to other researchers, they have no trouble adding more reservations to the list.

Danish Cancer Society: Exercise has very little effect on cancer

Gitte Laub Hansen from the Danish Cancer Society »completely understands their enthusiasm« when it comes to the possibility of being able to let patients know just how much exercise they need in order to prevent or treat cancer.

However, there continues to be some concerns, she points out. For instance, we have very little knowledge on how much participants in studies actually exercise. The studies are based mostly upon the participants own understanding, and most of us have a hard time remembering what exactly we have been doing.

Furthermore, we prefer to say that we have been exercising much more than we actually have. An additional concern, according to Gitte Laub Hansen, is that the knowledge we currently have on the effects of physical activity are quite small compared to that of smoking, unhealthy eating and overweight.

"Surely, exercise could help prevent obesity, which, next after smoking, is the number one risk factor for about 13 different types of cancer. It is an interesting perspective, but I have my doubts whether it would actually be possible", says Gitte Laub Hansen.

Scientists: We are far from

At the Danish hospital, Rigshospitalet, researcher Jesper Frank Christensen is studying how physical activity affects cancer, and how it could be combined with regular cancer treatment.

Jesper Frank Christensen is likewise part of the cancer group at the Centre for Physical Activity Research where they once discovered that cancer tumors in mice grows slower if the mice exercise.

He is part of a team currently looking into whether these results could be applied to humans, however, he is likewise cautious. The knowledge we currently have is mostly founded in small animal experiments and register based studies on human health, where it can be difficult to find certain correlations and causes as to why patients have become ill, Jesper Frank Christensen explains.

"These findings are the reason that the Danish Health Authority recommends cancer patients to be physically active, and of course, I support this. However, I still believe that we are far from being able to 'prescribe exercise as treatment'", he says.

"There continues to be too many questions we still do not know the answers to."

"We – as scientists – should be our own largest critics, and we should be careful not to let our excitement of the potential outshine what evidence can carry."

Physical activity as medication requires strong evidence

In Denmark, patients are already encourage to be physically active, but only if they want to.

The issue with making physical activity part of the established cancer treatment is, according to Jesper Frank Christensen, that we do not know why physical activity work, why the same types of activities do not work for everyone, or even how we are going to make people be physically active.

"If we encourage patients, who already has a hard time moving, that 'we know exercise makes you live longer, or your treatment work better', we are indirectly saying that they will be having a worse course of treatment if they do not."

"This requires strong evidence. Otherwise, we are putting an unreasonable amount of pressure on patients, and this might affect them negatively. It is unethical", believes Jesper Frank Christensen, post doc and team leader of Clinical Cancer Research at TrygFonden's Centre for Physical Activity Research.

Uncertain evidence may open up for criticism

There has been many studies on the correlation between physical activity and cancer.

However, according to Jesper Frank Christensen, many of them are of poor quality. For example, there has been too few participants or the researchers have not been sufficient in their description of the experiment. This makes it difficult to know exactly how their experiment has come to be, and to make comparisons of different studies.

Then there is the risk that patients, knowingly or unknowingly, have given biased feedback, or even experienced some kind of placebo effect from exercise. Overall, the combined evidence of the matter is, according to Jesper Frank Christensen, 'subject to great uncertainty'.

"I believe that the articles from ACSM is going to be overwhelming and positive", he says.

"However, I fear that if other scientists take a thorough look at the evidence, they will be able to ask a lot of critical questions, which would cause this field of research to experience a huge setback."

Patients are not exercising the way they should

The question is how much evidence we need in order to recommend physical exercise to patients. Kathryn H. Schmitz’ colleague, Joachim Wiskemann, is of the same opinion as his American colleague. Everything is not yet set in stone, but we simply need to get started.

Everyone would probably benefit from exercise, Wiskemann said at the Congress, no matter how hopeless it might seem for the individual. Joachim Wiskemann is leading a program that rehabilitates cancer patients using exercise.

In Prague, he told a story about a 77-year-old woman, who was suffering from lung cancer, osteoporosis and undergoing treatment for metastases because cancer had spread. Following three weeks, where the woman received help, she was able to do the exercises on her own.

The exercises included her getting down and up from a yoga mat. You can see the video of the 77-year-old woman from Joachim Wiskemann's presentation in the YouTube video above, or directly on YouTube. This video, which that was presented at the ECSS Congress, begins about 43:20 minutes in.

"We need to prescribe physical activity as medication. In this moment, less than twenty-five percent of cancer patients are getting enough exercise. Already there are programs all over the world, however, we need more projects in order to gain more knowledge as to how exercise works outside of scientific experiments. This is the reason why I want to encourage people in Europe to get started", Joachim Wiskemann proclaimed at the ECSS Congress.

Joachim Wiskemann is leading a program dedicated to the rehabilitation of cancer patients at NCT Heidelberg, and, just like his colleague, Kathryn H. Schmitz, assigned to Penn State University.

You can watch the video of the 77 year old woman from Joachim Wiskemann's presentation at the ECSS-conference in the youtube video posted above - around 43:20 min into it.

Are there any risks?

The primary risk of physical exercise is, according to Joachim Wiskemann, that patients might be injured in case they fall off the treadmill.

However, this is likewise something that Jesper Frank Christensen disagrees with, referring to a Norwegian experiment on High Intensity Training. The experiment was called off because an unexpected amount of patients suffering from testicular cancer became ill, from blood clots among others.

Experiments where cancer patients are doing physical activity, serious unintended incidents, such as hospital admissions or worsening of the patient’s condition are hardly ever recorded, unless it happens specifically during exercise. For that reason, we are not aware whether there might be an increased risk in the days following exercise, where the patients have pushed themselves physically.

"This is the reason why we need more controlled studies, making sure that this does not happen more often to patients who exercise regularly than it does to patients from the control group", adds Jesper Frank Christensen. Fortunately, these studies are coming.

Swedish researcher: New trial may provide answers

Professor Karin Nordin, who works at the Uppsala University in Sweden, does research on the rehabilitation of cancer patients. In collaboration with researchers from Rigshospitalet, she is currently looking into the effects of exercise.

Soon they will be able to present the results of a large randomized intervention study of 600 patients, who, over the course of six months, have been doing physical exercise while undergoing treatment.

"Our study provides answers to several of the questions raised here", writes Karin Nordin in an email to Science Nordic.

"Physical activities need to be individualized"

Even though Karin Nordin and Jesper Frank Christensen share much of the same opinion, their views on the matter are not entirely the same. Because unlike Jesper Frank Christensen, Karin Nordin is not sceptical about integrating physical activity in cancer treatment.

However, she does believe we need to be attentive to the fact that physical activity, much like other cancer treatment, needs to be accustomed to the individual patient.

"Physical activity needs to be individualized. It cannot simply be broadly implemented into our health care system", writes Karin Nordin, professor of public health at Uppsala University in Sweden and at the University of Adger in Norway.

Each year, 18.1 million people are diagnosed with cancer. 9.6 million People die from their illness. This makes cancer the world’s second leading cause of unnatural deaths, following cardiovascular disease.

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