Background: Many modifiable lifestyle factors have been associated with colon cancer risk, but less is known about their effect on disease when considered together. Estimating the proportion of colon cancer cases that could be prevented by the adoption of combined modifiable lifestyle behaviors will provide important insights into disease prevention.
Methods: In the Nurses' Health Study, we defined a low-risk group according to a combination of six factors: body mass index < 25 kg/m(2), physical activity of ≥ 21 metabolic equivalent of task per week, alcohol consumption ≤ 30 g/day, cigarette smoking <10 pack-years before the age of 30, current use of multivitamins for ≥ 15 years, and total calcium intake ≥ 700 mg/day. A composite risk score index was created and the population attributable risk (PAR%) was calculated after accounting for other known risk or protective factors.
Results: We documented 1,127 colon cancer cases among 81,092 over 24 years of follow-up. Compared with women in the lowest risk category, the women at all other exposure levels had a hazard ratio of colon cancer of 1.81 (95% confidence interval 1.15-2.85). The score index was significantly and linearly related to an increasing risk of colon cancer (p value for trend <0.0001). The PAR% of the six risk factors considered together in relation to colon cancer was 0.37 (95% CI 0.09-0.60). When regular aspirin use (two tablets/week for six or more years) was included with the other low-risk behaviors, the PAR% increased to 0.43 (95% CI 0.14-0.65).
Conclusions: Beyond the known benefit from colonoscopy/sigmoidoscopy, key behavior modifications and adherence to a healthy lifestyle could avoid approximately 37% of colon cancer cases among women.