What Does Smoking Do to the Digestive System?

Cigarettes are one of the most detrimental and systemically damaging legal substances one can consume. Every inhaled puff of smoke contains thousands of chemicals, hundreds of which are carcinogenic and teratogenic free radicals that damage every system in the body.
The negative effects of smoking on the lungs and respiratory tract are legion, and are well documented and well known by anyone not living under a rock for the last 40 years. However the effects of smoking do not end there. Smoking is a risk factor and contributor to dozens of disease processes that happen throughout the body, including the digestive tract. Key among them, according to the National Digestive Diseases Information Clearinghouse (NDDIC), smoking radically increases the risk of colon cancer, Crohn's disease, heartburn, gallstones, peptic ulcers and liver disease. In addition, heartburn is a known contributor to esophageal cancer, another disease which cigarette smoking also increases risks for.
These damaging processes happen because of a number of mechanisms. Perhaps most importantly, cigarette smoke contains hundreds of compounds that are known as free radicals, because they contain molecules that bond inappropriately with healthy tissue, causing the cells to break down and degrade, disordering DNA. Damage to the genetic material is one of the key causes of carcinogenesis, because cells replicate from the DNA, and when it is damaged, the cells are more likely to replicate out of control, which is the exact process by which cancer cells and tumors grow.
Other effects are less direct, but just as damaging. The free radicals also constrict blood flow, harming circulation. As circulation diminishes, cellular waste products, themselves toxins, build up and create synergistic damage with the free radicals. The free radicals, by definition, absorb and use up antioxidants. Many of the important antioxidants protect DNA, protect from sun damage, from oxidation and aging.
According to the American Diabetes Association, cigarette smoking has demonstrable effects on blood sugar, speeding the onset of diabetes-related vascular damage and likely effects blood sugar itself, making type two diabetes more likely. The diabetes process, alone, or more rapidly in combination with cigarette smoking, produces harmful compounds from sugars called Advanced Glycation End products, or AGEs. This handy acronym points out that cigarette smoking causes aging of all of the tissues, particularly the pancreas, which is an integral part of the digestive system.
Smoking affects the lymphatic system and the immune system in general, both of which have a strong relationship with the small intestine because of Peyer's patches, areas of lymphatic tissue that line and protect the small intestine.
Smoking also damages the liver, which may not seem like part of the digestive system at all, until you realize that all of the blood from the digestive system, laden with both nutrients and toxins from food, goes to the liver first, in a process called first-pass metabolism. Smoking constricts liver blood flow by the same process described above, as well as by delivering large amounts of toxins that need to be deactivated by the liver, taking up valuable liver processing ability and diminishing that ability simultaneously. In addition, smoking also causes constipation. Nicotine, like caffeine, initially stimulates peristalsis, the wavelike contraction of the muscle in the digestive tract that moves the digestate through the system. However, after long-term use, the body becomes dependent upon nicotine to produce peristalsis, eventually weakening peristaltic action and thereby causing constipation. It's a vicious cycle, because constipation puts additional load upon the liver due to the toxins that normally are excreted as stool then go back to the liver via the enterohepatic circulation, essentially a duct that goes from the large intestine to the liver. The effect is to both worsen toxicity and worsen constipation--the worse it gets, the worse it gets. The only solution is to get off nicotine and detoxify the liver.
In short, smoking affects every organ of the digestive system deleteriously, as it does all organs and tissues in the body. Because digestion and blood sugar regulation are central to health and longevity, smoking causes accelerated aging. If you're still smoking and have trouble quitting, ask for help. Many health insurance companies pay for cessation programs. Many natural therapies can help detoxify and reduce cravings. A 2002 study published by the "American Journal of Public Health" found that acupuncture and education, alone and together, significantly reduce smoking cravings and relapses.