Smoking cigarettes may cause Crohn’s disease, a new study confirms.
For the first time, researchers found exposure to chemicals in tobacco may increase the risk of developing the agonising condition.
South Korean scientists discovered mice who inhaled cigarette smoke showed signs of intestinal inflammation – a sign of Crohn’s disease.
Cigarette smoking activates specific white blood cells in the lung, which might later move to the colon, triggering bowel inflammation, they found.
It provides another reason for smokers to give up the notoriously bad habit, along with their increased risk of lung cancer and heart disease.
New treatments, or even a cure, for the debilitating bowel condition may be in the horizon due to the breakthrough findings.
For the first time, researchers found exposure to chemicals in tobacco may increase the risk of developing the agonising condition
Previous research has suggested smoking significantly increases the risk of Crohn’s disease. But the mechanism was unknown.
One explanation hypothesised was inflammation in the lungs caused by smoking could have a knock-on effect in the intestine.
A team of researchers at Kyung Hee University, Seoul, have now confirmed the initial suspicions in tests on rodents.
Confirming suspicions
Professor Hyunsu Bae, lead researcher, said: ‘The airways and the intestinal system have a lot in common.
‘Interestingly, in traditional Korean medicine, a connection between the lung and the large intestine has long been emphasised.
‘Crohn’s disease is more likely to occur in people with airway diseases, suggesting inflammation in the lungs is linked with inflammation in the gut.’
Professor Jinju Kim, co-author, added: ‘Smokers, especially those who also have bowel disease, should reduce their smoking.’
How was the study carried out?
For the study, published in Frontiers in Immunology, the mice were exposed to 20 cigarettes a day, six days a week, for a few weeks.
Cigarette smoking activates specific white blood cells in the lung, which might later move to the colon, triggering bowel inflammation, they found
Using tests, the researchers then examined the presence of inflammation in the mice’s lungs and bowels.
Unsurprisingly, compared with mice exposed to clean air, mice exposed to cigarette smoke showed significant inflammation in their lungs.
Interestingly, they also suffered from a type of colitis resembling Crohn’s disease, which is currently incurable.
The researchers found increased levels of mucus and inflammation in the colon, and blood in the faeces of the smoke exposed mice.
What did they find?
They also found increased levels of CD4+ T cells, a type of white blood cell, which were releasing a pro-inflammatory protein called interferon-gamma.
The team next investigated whether these white blood cells and inflammatory protein were responsible for the smoke induced colitis.
They repeated the experiment with mice that had very few CD4+ T cells and mice that couldn’t produce interferon-gamma.
In both cases, the mice did not develop colitis when exposed to cigarette smoke.
The team were now confident that CD4+ T cells were responsible for the cigarette smoke-induced colitis.
Confirming the theory
But they weren’t sure if it was possible for these white blood cells to be activated by cigarette smoke in the lungs, and then travel to the colon to cause colitis.
To test this, the researchers exposed mice to cigarette smoke, and then isolated CD4+ T cells from tissue near their lungs.
They then injected the cells into mice that had never been exposed to smoke.
The injected cells migrated to the colon, and the non-smoke-exposed mice developed colitis shortly after.