It is now proven that physical activity is linked to a reduced risk of several types of cancer. An article about a meta analysis based on nine prospective studies that was made with 750 thousand participants is recently published in the Journal of Clinical Oncology.
The article, which was prepared by scientists from The National Cancer Institute, The American Cancer Society and Harvard School of Publich Health, explains that in itself, the relationship between the level of physical activity and the risk of developing cancer has been established for a long time. However, the form of the relationship remains less clear and how much the usual level and type of activity, recommended in general to maintain a healthy standard of living, can be associated with a real reduction in this risk.
Today, the recommended level of physical activity for an average person is from two and a half to five hours a week, if it will be moderate-intensity exercises, or from an hour and a quarter to two and a half hours if high physical activity is preferred.
World Health Organization (WHO) refers to moderate physical activites as, for example, brisk walking, dancing, gardening or housework, games and activities with children and pets. For high intensity, running, climbing uphill, fast cycling and vigorous swimming, sports (football, hockey etc.), carrying heavy loads of over 20 kg or serious earthworks in the field are referenced.
A more standardized intensity level is explained in MET units, which shows a person’s metabolism speed during physical exertion to the level of his metabolism at rest. 1 MET is the amount of energy that is consumed at rest, equal to burning 1 kcal / kg / h.
A moderate exercise, according to the WHO, makes you move fast enough or vigorous to burn three to six times more energy per minute than at rest (from 3 to 6 MET), and high intensity exercises makes you burn more than six times (i.e. more than six MET).
In the analysis, researchers examined data from nine studies where respondents gave self reports about the level of physical activity and examined the relationship between this level and 15 types of cancer.
They found that when following the simplest recommendations of physical activity (from 7.5 to 15 hours MET per week, which corresponds to two and a half hours of exersize or more), the risk of getting a family of fifteen cancers was statistically reduced. Moreover, for some types of cancer, scientists found a dose and response relationship: The more hours and MET, the greater the risk reduction.
For some others, dependence on having a sufficient level of activity was important to reduce the risk, but increase in the number / intensity of exercise did not further lead to a corresponding risk reduction.
Physical activity was associated with a lower risk of developing colon cancer in men (8% for 7.5 hours per week; 14% for 15 hours per week), breast cancer in women (6-10%), and endometrial cancer (10% – 18%), kidney cancer (11-17%), myeloma (14-19%), liver cancer (18-27%) and non-Hodgkins lymphoma (11-18% in women). The dose-dependent response was linear in form for half of the associations and non-linear for the rest.
Scientists note that more research is needed for more accurate and general data. They have noted the incompleteness of the tested types of cancer (there are of course much more than 15 of them), insufficient ethnic diversity in samples, insufficient differentiation by activity types and the reporting made based on the subjects’ own assessment.