Physical activity, diet, and risk of colon cancer in Utah.

A population-based case-control study was used to assess the relations of physical activity and diet to the development of colon cancer in Utah. Data were obtained for a reference period of two years prior to interview for controls (204 females and 180 males) and two years prior to the date of diagnosis for cases (119 females and 110 males). Both leisure time and occupational activities were ascertained by level of intensity and were converted to calories expended per week for analysis. Dietary data were obtained from a quantitative food frequency questionnaire. Physical activity and dietary data were divided into quartiles based upon the distribution in the study population for analyses. Total physical activity was protective against the development of colon cancer for both males (odds ratio (OR) = 0.70) and females (OR = 0.48) when high and low quartiles of activity were compared. Intense physical activity was the component of activity that had the greatest protective effect for males (OR = 0.27); a similar relation was seen for females (OR = 0.55). The observed relation between physical activity and colon cancer was not confounded by dietary intake of calories, fat, or protein, nor was the diet and colon cancer relation confounded by physical activity (odds ratios for calories, protein, and fat in males were 2.40, 2.57, and 2.18, respectively). Assessment of the interrelations among physical activity, diet, and colon cancer suggests that physical activity modifies colon cancer risk associated with diet.