Smokeless tobacco products, including chewing tobacco, snus, and snuff, are often mistakenly viewed as a safe alternative to smoking. These products are not burned but are placed in the mouth, allowing nicotine and other substances to be absorbed through the oral tissues. While smoking risks are widely known, the health effects of smokeless tobacco beyond the mouth are often misunderstood. This article explores the specific compounds in smokeless tobacco and the evidence linking its use to colorectal cancer risk.
Carcinogenic Compounds in Smokeless Tobacco
Smokeless tobacco products contain more than 28 cancer-causing chemicals. The most potent and abundant carcinogens are Tobacco-Specific Nitrosamines (TSNAs). These chemicals, such as N’-nitrosoninotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), are not naturally present in the tobacco leaf.
TSNAs form during the curing, fermentation, and aging processes, transforming nicotine and other alkaloids into potent carcinogens. The concentration of TSNAs varies dramatically between different types of smokeless tobacco products. Smokeless tobacco also contains other harmful substances, including heavy metals like arsenic, cadmium, and lead, as well as radioactive materials like Polonium-210.
Systemic Absorption and Internal Exposure
Carcinogens in chewing tobacco are readily absorbed and circulated throughout the body, not remaining confined to the mouth. When the tobacco is held against the cheek or gum, nicotine and TSNAs are absorbed directly into the bloodstream through the oral mucous membranes. This absorption method bypasses the lungs and delivers a sustained, high dose of nicotine and carcinogens to the user.
Once in the bloodstream, these compounds travel to the liver for metabolic processing. During this process, TSNAs are activated into compounds that damage DNA in cells throughout the body. These activated carcinogens circulate and reach distant organs, including the cells lining the digestive tract. This provides a biologically plausible mechanism for causing cancer in the colon and rectum. Systemic exposure is compounded because users often swallow the tobacco juices, directly introducing carcinogens into the esophagus and stomach.
Epidemiological Evidence Linking Smokeless Tobacco to Colon Cancer
The scientific evidence directly linking smokeless tobacco use to colorectal cancer is less definitive than the established links to oral, esophageal, and pancreatic cancers. Studies often focus on snus, a moist powder smokeless tobacco product primarily used in Scandinavia. For example, a pooled analysis of nine large Swedish cohort studies, involving over 400,000 men, found no clear association between overall snus use and the incidence of colorectal cancer.
However, that same analysis noted a statistically significant increased risk specifically for rectal cancer among exclusive current snus users. Similarly, a 26-year follow-up study of American veterans observed that the risk of death from rectal cancer was significantly elevated among users of chewing tobacco or snuff. These findings suggest that while the overall link to colorectal cancer may be inconsistent, a specific risk to the rectum may exist, particularly with long-term use. Epidemiological research is challenged by isolating the effect of smokeless tobacco from other common risk factors, such as diet, physical activity, and concurrent cigarette smoking.
Other Established Cancer and Health Risks
While the evidence for colon cancer is still developing, smokeless tobacco is unequivocally established as a cause of several other serious health conditions. The most recognized cancer risks are to the tissues in direct contact with the product, specifically the oral cavity, including the lip, tongue, and cheek. Smokeless tobacco is also a confirmed cause of cancers of the esophagus and the pancreas, where the carcinogens are absorbed and distributed.
Beyond cancer, smokeless tobacco causes severe damage to oral health. This damage includes leukoplakia, which are white or gray patches in the mouth that can become cancerous. It also significantly contributes to gum recession, periodontal disease, and tooth loss. The high nicotine content, often absorbed at levels comparable to or higher than smoking, poses non-cancer risks, including increased heart rate and elevated blood pressure, contributing to a higher risk of death from heart disease and stroke.