Consumption of milk and calcium and higher blood levels of vitamin D appear to decrease colorectal cancer risk. Regular use of nonsteroidal anti-inflammatory drugs, such as aspirin, also reduces risk. However, these drugs are not recommended for the prevention of colorectal cancer among individuals at average risk because they can have serious adverse health effects. Study results are mixed about the association between menopausal hormone therapy and colorectal cancer.
source:American Cancer Society. Cancer Facts & Figures 2013. Atlanta: American Cancer Society; 2013