An analysis published in the American Journal of Epidemiology calculated the incidence and relative risk of colon cancer in women up to age 70. The data came from the Nurses’ Health Study and included 83,767 women who were ages 30 to 54 when the investigation began in 1976. The women were followed for 24 years.

Modifiable risk factors had a great cumulative effect on the risk of colon cancer.  A woman who didn’t exercise, was consistently overweight, ate red or processed meat daily, consumed low levels of folate, and hadn’t been screened for colon cancer was almost four times as likely to develop colon cancer by age 70 as a woman with a low-risk lifestyle (regular exercise, low red and processed meat consumption, low relative weight, and adequate folate). 

A high level of physical activity (measured in metabolic equivalents, or METs) was especially important. Women who reported 21 MET hours per week (equivalent to about seven hours per week of brisk walking) were half as likely to develop colon cancer as women who got only two MET hours per week (equivalent to walking slowly for one hour per week).

Another study, by Arem et al, published in the Journal of Clinical Oncology, compared survivors of colorectal cancers reporting more than 7 hours per week of pre-diagnosis leisure time physical activity (LTPA), with those reporting no LTPA, found a 20% lower risk of all-cause mortality. Post-diagnosis LTPA of ≥ 7 h/wk, compared with none, was associated with a 31% lower all-cause mortality risk, independent of pre-diagnosis activity.