Description of the Evidence
A large cohort study found a dose-response relationship between alcohol intake and death from CRC, with a RR of 1.2 (95% CI, 1.0-1.5) for four or more drinks per day compared with nondrinkers.
Most case-control studies of cigarette exposure and adenomas have found an elevated risk for smokers. In addition, a significantly increased risk of adenoma recurrence following polypectomy has been associated with smoking in both men and women. In the Nurses' Health Study, the minimum induction period for cancer appears to be at least 35 years. Similarly, in the Health Professionals Follow-up Study, a history of smoking was associated with both small and large adenomas and with a long induction period of at least 35 years for CRC. In the Cancer Prevention Study II (CPS II), a large nationwide cohort study, multivariate-adjusted CRC mortality rates were highest among current smokers, intermediate among former smokers, and lowest in nonsmokers, with increased risk observed after 20 or more years of smoking in men and women combined. On the basis of CPS II data, it was estimated that 12% of CRC deaths in the U.S. population in 1997 were attributable to smoking. A large population-based cohort study of Swedish twins found that heavy smoking of 35 or more years' duration was associated with a nearly threefold increased risk of developing colon cancer, though subsite analysis found a statistically significant effect only for rectal but not colon cancer. Another large population-based case-control study supports the view that current tobacco use and tobacco use within the last 10 years is associated with colon cancer. A 50% increase in risk was associated with smoking more than a pack a day relative to never smoking. However, a 28-year follow-up of 57,000 Finns showed no association between the development of CRC and baseline smoking status, though there was a 57% to 71% increased risk in persistent smokers. No relationship was found between cigarette smoking, even smoking of long duration, and recurrence of adenomas in a population followed for 4 years after initial colonoscopy.
A meta-analysis of 106 observational studies found a RR (ever smokers compared with nonsmokers) for CRC incidence of 1.18 (95% CI, 1.11-1.25), with an absolute risk increase of 10.8 cases per 100,000 person-years (95% CI, 7.9-13.6). There was a statistically significant dose-response effect. In 17 studies with data on CRC mortality, cigarette smoking was associated with CRC death, with a RR (ever smokers vs. never smokers) of 1.25 (95% CI, 1.14-1.37), and an absolute increase in the death rate of 6.0 deaths per 100,000 person-years. For both incidence and mortality, the association was stronger for rectal cancer than for colon cancer.