[Physical inactivity and cancer--is this a causal relationship?]

Strong epidemiological evidence suggests relationship to exist between physical inactivity and the risk of large bowel cancer (especially colon cancer). Moreover, there are indications that inactivity is also associated with an increased risk of endogenous hormone-related cancer (especially breast cancer). However, further research is needed to determine whether such relationships are casual, and if so to identify the underlying mechanisms. Since a large proportion of the populations of industrial countries are characterized by a sedentary lifestyle, even a small risk may be associated with high attributable fraction. Moreover, not only are the types of cancer concerned common, but inactivity is also associated with a number of other chronic diseases. Accordingly, the health benefit to be derived from a general increase in physical activity might be substantial.