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Physical activity and cancer: stats and evidence

The evidence linking physical inactivity to cancer. This page explains how we know that being active can reduce the risk of cancer. There is an overview of the scientific evidence and further links so you can find out more if you wish.

 

Being inactive can increase the risk of cancer

Scientists have shown that low levels of physical activity can increase the risk of certain cancers 1, 2. A study published in December 2011 estimated that around 1% of cancers in the UK, more than 3,000 cases every year, are linked to people doing less than government guidelines for physical activity each week 3.

Inactive lifestyles can lead to many other health problems. These include diabetes, osteoporosis, stroke and heart disease. A study published as part of a Lancet special series on physical activity and global health estimated that 5.3 million of the 57 million deaths worldwide in 2008 were down to physical inactivity 4.

Regular physical activity also helps to keep body weight at a healthy level, and being overweight or obese can greatly increase the risk of cancer. But the activity itself also has a protective effect, which is independent of its effects on bodyweight 1, 2.

Being more active can reduce the chances of dying early - reports pooling data from several studies found that the more active people were, the longer they lived 5, 6.

 

Physical activity reduces the risk of bowel cancer

Many studies from around the world have investigated the link between physical activity and bowel cancer. Overall, the evidence shows that people who do the most physical activity can cut their risk of developing cancer of the large bowel (colon) by about a quarter 7, 8. Being active seems to cut the risk of cancer developing in any part of the colon (which accounts for around two thirds of all bowel cancers in the UK). But it may not have any effect on the risk of rectal cancer 8, 9.

People who do the most physical activity may have a smaller chance of developing polyps (adenomas), small growths on the lining of the bowel which can go on to become cancer 10.

Physical activity can reduce the risk of bowel cancer in many different ways 1, 2.

  • Physical activity leads to regular bowel movements. So cancer-causing substances in undigested food pass through the bowel more quickly.
  • Physical activity reduces the levels of insulin, some hormones and some growth factors. At high levels, these substances can encourage the growth of tumours.
  • Physical activity can change the levels of chemical messengers called prostaglandins, which are involved in inflammation. Reducing inflammation in the bowel could mean cells aren't multiplying as quickly, so there's less chance of the mistakes during cell replication that could lead to cancer.

 

 

Physical activity reduces the risk of breast cancer

An analysis combining the results of 31 studies on physical activity and breast cancer found that the women who did the most activity had a 12% lower risk of developing breast cancer compared with the least active women 11. The analysis also showed that the more activity a woman does, the more she can reduce her risk of breast cancer. For example, for every 2 hours a week a woman spends doing moderate to vigorous activity, the risk of breast cancer falls by 5%.

And it isn't just women in a physically active job, or those doing recreational exercise, who can see the benefits - heavier chores such as ironing, gardening and cleaning can help reduce the risk of breast cancer too 11. Research including the EPIC study, which includes over a quarter of a million European women, consistently shows that household activity can reduce a woman's risk of developing breast cancer. Housework formed the biggest part of women's activity in the EPIC study and reduce the risk of breast cancer by itself and in combination with leisure time activity like walking, cycling or playing sport 11, 12.

As with bowel cancer, physical activity probably reduces breast cancer risk by lowering levels of insulin, hormones and growth factors 1, 2, 11.

Physical activity reduces the risk of womb cancer

A 2010 analysis of five studies into physical activity and womb (uterine) cancer risk concluded that physical activity was clearly associated with reduced risk of the most common type of the disease (endometrial cancer), with active women having around 30% lower risk than inactive women 13.

Physical activity could lower the risk of womb cancer because it reduces the level of oestrogen in the blood as well as the amount of circulating insulin 13.

 

Physical activity may also reduce the risk of other cancers

Large evidence reviews by the World Health Organisation and the World Cancer Research Fund have suggested that being physically active might reduce the risk of other cancers too, although there hasn't been enough good evidence published for them to say for sure. Cancers that may also be prevented by being active include lung and prostate cancers 1, 2, 14.

Studies that bring together the findings of previous research have found that people who do higher levels of activity have a lower risk of developing lung cancer - but smoking and previous lung diseases could have affected these findings 15, 16. Still, similar results have been found when comparing activity levels only among people who smoke - so smoking wouldn't explain this effect 17. But there is still a question over whether physical activity itself is responsible for the difference in lung cancer risk. The relationship could work the other way around - people with healthier lungs may be more likely to be active.

Some, but not all, studies investigating a link between physical activity and prostate cancer have found that more active men have a lower risk of developing the disease. A recent summary of the evidence concluded that being active, particularly in the workplace, could slightly reduce a man's chance of being diagnosed with prostate cancer 18. But many of the studies included were of lower quality, so it's hard to conclusively rule out chance as an explanation. Research into prostate cancer and lifestyle can be difficult to interpret, because prostate cancer is not only very common, but some types don't cause a man any harm and he may not even know he has the disease. Particularly with the development of techniques like PSA testing that can pick up cancers that would otherwise never have been diagnosed, this makes it difficult for researchers to know the true numbers of men with prostate cancer in their study.

 

Physical activity guidelines

Based on the current evidence, many health organisations have recommended people should do moderate physical activity on a regular basis 2, 19, 20.

The UK guidelines for physical activity are 21:

  • Early years (under five years): After beginning to walk, under-fives should be physically active for at least 180 minutes a day;
  • Children and young people (5 - 18 years): At least 60 minutes of moderate to vigorous physical activity per day. Vigorous intensity activities that strengthen muscle and bone should be carried out on at least three days a week;
  • Adults (19+ years): At least 150 minutes of moderate intensity physical activity over a week, in bouts of 10 minutes or more. Physical activity to improve muscle strength should be carried out on at least two days per week.

The guidelines are a minimum recommended level. In general the more exercise you do, (whether that's through exercising longer or more vigorously), the greater the benefits for your health are likely to be 5, 11.

 

It’s never too late to start keeping fit

An American study looked at over 10,000 men, some of whom had been inactive for years. Those who took up moderate regular exercise managed to reduce their risk of premature death by about a quarter 22.

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References

  1. IARC, Weight Control and Physical Activity. IARC Handbooks of Cancer Prevention, ed. H. Vainio and F. Bianchini. Vol. 6. 2002, Lyon: IARC.
  2. WCRF and AICR. Food, nutrition, physical activity and the prevention of cancer: A global perspective. 2007, Washington: American Institute for Cancer Research. Link.
  3. Parkin, M., et al., The fraction of cancer attributable to lifestyle and environmental factors in the UK in 2010. BJC 2011. 105(Supp 2): S38-S41. PubMed.
  4. Lee, I., et al. Effect of physical inactivity on major non-communicable diseases worldwide: an analysis of burden of disease and life expectancy. Lancet, 2012. 380: p. 219-29. PubMed.
  5. Moore., S.C., et al. Leisure time physical activity of moderate to vigorous intensity and mortality: a large pooled cohort analysis. PLoS Med, 2012. 9(11): e1001335. PubMed.
  6. Samitz, G., et al. Domains of physical activity and all-cause mortality: systematic review and dose-response meta-analysis of cohort studies. Int J Epidemiol, 2011. 40(5): p. 1382-400. PubMed.
  7. Wolin, K., et al. Physical activity and colon cancer prevention: a meta-analysis. Br J Cancer, 2009. 100(4): p. 611-6. PubMed.
  8. Robsahm, T.E., et al. Body mass index, physical activity, and colorectal cancer by anatomical subsites: a systematic review and meta-analysis of cohort studies. Eur J Cancer Prev, 2013. PubMed.
  9. Boyle, T., et al. Physical activity and risks of proximal and distal colon cancers: a systematic review and meta-analysis. J Nat Cancer Inst, 2012. 104(20): p. 1548-61. PubMed.
  10. Wolin, K., et al. Physical activity and risk of colon adenoma: a meta-analysis. Br J Cancer, 2011. 104(5): p. 882-5. PubMed.
  11. Wu, Y., et al. Physical activity and risk of breast cancer: a meta-analysis of prospective studies. Breast Cancer Res, 2013. 137(3): p. 869-82. PubMed.
  12. Steindorf, K., et al. Physical activity and risk of breast cancer overall and by hormone receptor status: The European Prospective Investigation into Cancer and Nutrition. Int J Cancer, 2013. 132(7): p. 1667-78. PubMed.
  13. Moore, S.C, et al. Physical activity, sedentary behaviours, and the prevention of endometrial cancer. Br J Cancer 2010. 103 (7): 933-8. PubMed.
  14. Friedenreich, C., et al. State of the epidemiological evidence on physical activity and cancer prevention. Eur J Cancer, 2010. 46(14): p. 2593-604. PubMed.
  15. Tardon, A., et al. Leisure-time physical activity and lung cancer: a meta-analysis. Cancer Causes Control, 2005. 16(4): p. 389-97. PubMed.
  16. Sun, J., et al. Physical activity and risk of lung cancer: a meta-analysis of prospective cohort studies. Asian Pac J Cancer Prev, 2012. 13(7): p. 3143-7. PubMed.
  17. Buffart, L., et al. Physical activity and the risk of developing lung cancer among smokers: a meta-analysis. J Sci Med Sport, 2013. PubMed.
  18. Liu, Y., et al. Does physical activity reduce the risk of prostate cancer? A systematic review and meta-analysis. Eur Urol, 2011. 60(5): p. 1029-44. PubMed.
  19. Boyle, P., et al., European Code Against Cancer and scientific justification: third version (2003). Ann Oncol, 2003. 14(7): p. 973-1005. PubMed.
  20. Kushi, L.H., et al. American Cancer Society Guidelines on nutrition and physical activity for cancer prevention: reducing the risk of cancer with healthy food choices and physical activity. CA Cancer J Clin, 2012. 62(1): p. 30-67. PubMed.
  21. Start active, stay active: A report on physical activity from the four home countries' chief medical officers. Department of Health, Physical Activity, Health Improvement and Protection, 2011. Link.
  22. Paffenbarger, R.J., et al., The association of changes in physical-activity level and other lifestyle characteristics with mortality among men. N Engl J Med, 1993. 328: p. 538-545. PubMed

 

Updated: 16 August 2013