For most people smoking is simply a bad idea. Chronic smokers are at significantly greater risk for numerous ailments, including lung and mouth cancer, heart disease, chronic obstructive pulmonary disease, and respiratory tract infections. After centuries of use and abuse, we’ve catalogued the harm tobacco can do in staggering detail. It’s safe to say that smoking is bad for your health.

But the role of smoking in the development and progression of inflammatory bowel disease (IBD) is not as straightforward as you might expect. Research shows that smoking is clearly detrimental in Crohn’s disease. But it also indicates that, among current smokers, stopping smoking may actually cause a flare in patients with ulcerative colitis.

A recent study concluded, for example, that among women in the longterm Nurses’s Health Study, current smoking was not associated with an increased risk of ulcerative colitis. But being a former smoker was significantly linked to a greater risk of colitis. This increased risk peaked within two to five years after quitting, and persisted for more than 20 years after smoking cessation. Something about tobacco smoke is evidently beneficial to people with ulcerative colitis, or protective against its development.

Tobacco Smoke and Ulcerative Colitis

The list of chemicals in cigarette smoke is long, measuring in the thousands. Perhaps the best known is nicotine. Nicotine is an addictive drug that is classified as a stimulant. It’s also psychoactive, meaning that it affects the brain. Nicotine binds with specific receptors in the brain and promotes the release of messenger chemicals—neurotransmitters—such as dopamine, which in turn activate the brain’s reward circuitry. It also stimulates the release of epinephrine (adrenalin).

Research suggests that nicotine is the active ingredient that has an impact on the progression of ulcerative colitis symptoms. Accordingly, some doctors have prescribed transdermal nicotine replacement therapy (the nicotine patch) for their ulcerative colitis patients. This nicotine treatment for ulcerative colitis has met with some success, but results have been mixed. Because of its ability to stimulate the release of adrenalin, some patients experience unpleasant side effects, such as headaches, nervousness, a racing heart, or sweating. Some people find these side effects too unpleasant and discontinue therapy.

Most experts still think the risks of smoking outweigh the potential advantages. Indeed, smoking is still clearly associated with worse outcomes among people with Crohn’s disease. Even secondhand smoke exacerbates Crohn’s symptoms, and it’s linked to significantly worse treatment outcomes.

Research has consistently indicated that current smokers with ulcerative colitis tend to have fewer and less severe disease flare-ups. Some experts have even described ulcerative colitis as a disease of non-smokers and former smokers.

Given the known health risks of smoking, experts have been understandably cautious about encouraging smoking among their ulcerative colitis patients. Even so, the relationship between ulcerative colitis and smoking suggests a possible role of nicotine in the treatment of it. But how could smoking be beneficial to ulcerative colitis patients when its effects on virtually every other aspect of health is adverse? We may finally have an answer. Researchers recently reported that smoking appears to alter the makeup of the various types of “friendly” bacteria living in the intestinal tract.

Smoking and the Intestinal Microbiota

These bacteria—the intestinal microbiota—are increasingly emerging as crucial (and formerly overlooked) players in the maintenance of overall health. Ongoing research shows that the intestinal microbiota—meaning the specific mixture of many different species of bacteria and other microorganisms living in the intestinal lining—plays an important role in various aspects of health, ranging from the regulation of the immune system, to aiding digestion, to regulating metabolism. They are even thought to influence mood, body weight, and other aspects of health.

New advances in DNA-sequence based technologies (metagenomics) have allowed scientists to study the genetic makeup of microbial populations with unprecedented rapidity and ease. These advances have led to a deeper—and still unfolding—understanding of the role of gut microbes in health. The relationships among intestinal microbes and the immune system are of particular relevance to our understanding of inflammatory bowel disease.

It is now thought that tobacco smoke affects the microbiota, altering it in some key way. Ulcerative colitis is an immune disease; it occurs when a person’s immune system mistakenly attacks and destroys the tissues of the colon. In some as yet unknown way, tobacco smoke appears to alter the mixture of bacteria living in and on the gut lining (the mucosa). This in turn apparently dials down the flames of inflammation, resulting in fewer flare ups of disease activity.

Stopping smoking is a risk factor for worse outcomes among ulcerative colitis patients who currently smoke. The fact that smoking confers some measure of protection against flare ups presents new opportunities for investigation into the role of the gut microbiota in IBD, and suggests the possibility that new treatments may one day be forthcoming. If you’re a current smoker with ulcerative colitis, the overall impact smoking has on your health would still support your goal of trying to quit; however, it might be helpful to at least discuss the best time to quit with your physicians.