Age-standardized risk factors for colorectal cancer in relation to lifetime number of blood donation in the Health Professionals Follow-up Study.

1Body mass index was calculated as weight in kilograms divided by the square of height in meters.2MET denotes metabolic equivalent. MET-hours = sum of the average time/week spent in each activity x MET value of each activity.3Regular aspirin user was defined as consumption of 2 or more 325-mg tablets per week. Non-regular user was defined otherwise.4Intakes were estimated with food-frequency questionnaire in 1990 except for iron supplement use from the 1992 questionnaire.5Nutrient values were energy-adjusted intake.6The serum ferritin levels were measured in a random sample of 305 men in HPFS.