NEW YORK (Reuters Health) - Cigarette smoking appears to promote the development of polyps in the colon, especially those that are more likely to progress to cancer, a research review suggests.
In an analysis of 42 studies, researchers found that current smokers were twice as likely as nonsmokers to develop colon polyps. Former smokers also showed a heightened risk, though it was less than that of current smokers.
What's more, the analysis found, smoking was particularly linked to "high-risk" polyps; while most colon polyps are not dangerous, high-risk ones are relatively more likely to become cancerous.
The findings offer "strong evidence" that cigarette smoking contributes to both the formation of polyps and their aggressiveness, said Dr. Edoardo Botteri, of the European Institute of Oncology in Milan, Italy.
He and his colleagues report the results of their review in the journal Gastroenterology.
While smoking does appear to be a risk factor for polyps, past studies have been mixed as to whether it raises the risk of colon cancer itself.
This paradox may be explained by the design of the studies, according to Botteri's team. For example, many studies may not have followed smokers for a long enough period; any heightened colon cancer risk from smoking could take decades to emerge.
The current findings suggest that people who refrain from smoking can lower their risk of polyps and, potentially, colon cancer, Botteri told Reuters Health.
They also raise the possibility that smokers would benefit from earlier colon cancer screening, according to the researchers.
As it stands, adults are advised to start colon cancer screening at the age of 50, though people at higher-than-average risk -- such as those with ulcerative colitis, or a family history of colon cancer -- often start earlier.
Some experts have already suggested lowering the screening age for longtime smokers, Botteri and his colleagues note, but this is not yet standard practice.
Colon polyps typically emerge after age 50, and the large majority of colon cancers develop after this age as well. According to Botteri, it's still not clear whether smokers tend to develop polyps at an earlier-than-average age, or whether their polyps tend to progress more rapidly to cancer.
What is clear, he said, is that both current and former smokers should be especially vigilant about following the current recommendations on colon cancer screening.
SOURCE: Gastroenterology, February 2008.