eOver the past 60 years, experts have documented a sharp rise in the incidence of both ulcerative colitis and Crohn’s disease—the two medical conditions that make up most cases of inflammatory bowel disease (IBD). For decades, this rise was limited to North America, Western Europe, and other industrialized nations. Although there is some evidence that the rise in IBD has slowed or even plateaued in these locations, IBD is becoming more common in newly industrialized countries in Asia and other parts of the world.
There is no doubt that genetic factors play a role in the risk of inflammatory bowel disease—and especially Crohn’s disease. But the increasing incidence of IBD and the distinct geographic patterns of the disease strongly suggest that environmental factors are also at play. “Since World War II, we have seen a rapid increase in the incidence of IBD throughout the developed world,” says Dr. Gilaad Kaplan, professor and gastroenterologist at the University of Calgary in Canada. “Something about the Western way of life seems to allow this disease to thrive.” What is that something? This is the unsolved mystery.
There are several theories—or rather, suspects. Researchers have found links between IBD and Air Pollution, dietary supplements, early-life antibiotic exposure, and other environmental variables. Kaplan says that several of these risk factors, not just one, likely underlie increases in IBD. And they all have one thing in common: the gut microbiome. “Most people think that what drives the inflammatory response that we see when the body’s immune system attacks the gut lies in the gut microbiome,” he says.
Your gastrointestinal tract is inhabited by billions of microorganisms that are critical to the health and function of your gut. These bacteria help digest the foods you eat, and the metabolites they produce help regulate your immune system. Kaplan says that healthy and a diverse microbiome is a hallmark of a healthy GI tract, while anything that disrupts or imbalances the microbiome is associated with GI dysfunction, including IBD. “Many of the environmental risk factors that have been widely studied are now being looked at through the lens of the microbiome,” he says. This new perspective leads to important insights, including some relevant to the treatment of IBD.
Here you will find a summary of the environmental risk factors that researchers have associated with IBDas well as expert guidance on limiting these risks.
Air pollution and IBD
For a first-of-its-kind study published in 2010, researchers examined the relationship between ambient air pollution and the incidence of IBD. They found that young people who grew up around high concentrations of nitrogen dioxide were more than twice as likely as other children to develop Crohn’s disease.
Since this groundbreaking study, more work has linked air pollution to higher rates of IBD. “We found that exposure to nitrogen dioxide and ozone at an early age is associated with increased risks,” says Eric Lavin, a senior epidemiologist at Health Canada (the Canadian government’s equivalent of the US Department of Health and Human Services).
Both pollutants are related to car traffic. Fuel-powered cars and trucks emit nitrogen dioxide in their exhaust gases. When this nitrogen dioxide mixes with heat and sunlight, it undergoes a chemical reaction that produces ozone. “In areas where there is a lot of traffic, we may see increased levels of this combination,” Lavin says. “Living in close proximity to these areas can be a risk factor for IBD.”
How can air pollution affect gut health? Research shows that after inhaling pollutants, the lungs can actually push them down the throat so they can be swallowed. This process is known as mucociliary clearance. Once in the gut, Lavin says, these pollutants can cause damage to the gut microbiota in ways that promote inflammation.
Based on his work and that of others, he says exposure to air pollution during childhood — not in the womb or in adulthood — appears to pose the greatest risk of IBD. Staying away from busy roads, especially on hot sunny days, is one way to avoid these risks. “The levels of these pollutants are highest within 50 meters” — about 160 feet — “of busy roads,” he says.
Lavigne also looks at the effect of parks and other urban green spaces on air pollution risks. His research found that children who grew up near green spaces had a reduced risk of IBD. “Particles in the air can be trapped by tree leaves, so having more trees and greener environments can actually create a buffer that reduces human exposure,” he explains.
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Food choices and dietary exposures
The things you ingest can affect the composition of your microbiome and therefore the health of your gut. And researchers have identified a number variables related to diet which appear to play a role in IBD risk.
Some of the strongest activities include the first foods a newborn swallows. “Breastfeeding seems to be very important,” Kaplan says. Research shows that children who are breastfed, as opposed to formula-fed children, are more than 25% less likely to develop IBD. “As a baby, when you have breast milk, there seem to be tangible benefits that support the development of a healthy and diverse microbiome,” he explains.
Beyond infancy, there is evidence that consumption sweet drinks— especially soft drinks — increase a person’s risks of ulcerative colitis. The more soda someone consumes, the higher the risk. On the other hand, eating vegetables is associated with lower rates of ulcerative colitis, while eating whole fruits or other fiber-rich foods appears to reduce a person’s risks of Crohn’s disease.
“There’s also some really interesting research on preservatives that extend the shelf life of food,” Kaplan says. A 2021 study in the journal BMJ found that a higher intake of ultra-processed foods—soft drinks, but also salty snacks, processed meats, and other packaged goods—was associated with a sharp rise in IBD. Compared to people who ate less than one serving of these foods per day, those who ate five or more servings had nearly double the risk of IBD.
“Things like emulsifiers and additives and highly processed food particles can actually lead to changes in the microbiome that can be associated with IBD risk,” Kaplan says. “Choosing whole foods and staying away from things that are processed or packaged can lower your risks.”
Hygiene at an early age and antibiotics
antibiotics it can save a life when someone has a bacterial infection. But these drugs kill indiscriminately—meaning they eliminate both good bacteria and bad bacteria. And there is evidence that when taken at an early age, while a child’s microbiome is still forming, antibiotics can cause imbalances that promote IBD.
“Antibiotics can alter the composition of the intestinal gut microbiota by reducing taxonomic richness and diversity,” write the authors of a 2019 study in the journal Gastroenterology. They cited work linking the use of broad-spectrum antibiotics at an early age—anything but penicillin, in fact—with a greater than 50% increase in the risk of IBD.
“If you have a bacterial infection, you need antibiotics,” Kaplan says. But all too often, these drugs are prescribed when they aren’t really needed — for example, when a child has a respiratory infection that would likely resolve on its own without antibiotics. Doctors are increasingly aware of the risks associated with overuse of antibiotics. But parents still need to be cautious, he says.
Meanwhile, while hygiene is generally thought of as a good thing—and not just a good thing, but a safety measure that has saved countless lives—there is strong evidence that excessive cleanliness, especially in infancy and childhood, can actually weaken the microbiome. of the intestines. The “hygiene hypothesis,” as it’s called, posits that children who interact with siblings, farm animals, pets, dirt, and other sources of germs tend to have healthier and more resilient gut microbial ecosystems, and research links all these factors with lower rates of IBD (as well as allergies and autoimmune diseases).
“Exposure at an early age [to germs] has an important programmatic role on the microbiome and the immune system,” says Dr. Emeran Mayer, founding director of the Microbiome Center at the University of California, Los Angeles. The theory is that when the developing microbiome encounters microbes and bacteria, this exposure trains its sensitivity and reactivity in ways that reduce IBD risks. And so raising children in a squeaky clean environment and separate from other children, animals or sources of germs can jeopardize their gut health as well as their immune competence. (Some experts even speculate that safety measures against COVID-19, such as heavy use of hand sanitizers, may inadvertently lead to an increase in IBD among young people.)
A complex puzzle
Although researchers have made great strides in studying the environmental risk factors of IBD, they say the relationship between a person’s gut health and these variables is extremely complex. “The risks for someone may be completely different in the womb, in childhood, or in adulthood,” Kaplan points out. He gives the example of smoking cigarettes. It may be that smoking during adolescence, to a greater extent than in adulthood, is a greater risk factor for bowel disorders. Or vice versa. A person’s risk may also depend on the amount they smoke, as well as their genetic predisposition to gastrointestinal disease. “There are so many variables that create so much heterogeneity,” he says. “It’s very difficult to say this is a risk factor and it’s not.”
With that caveat in mind, Kaplan says there are steps everyone can take to reduce their IBD risks. “These are often things that promote healthy living in general,” he says. “Eating more whole foods, getting regular exercise and trying to reduce stress in your life are all on the checklist I go through with patients.” For those who live in parts of the country where sunlight is scarce, he says that taking a vitamin D supplement may be helpful. “If you look at people who have IBD, you often see vitamin D deficiency,” he explains. This may just be a byproduct of the condition, not its cause. Still, he says that taking a daily supplement of 1,000 IU is low-risk protection against gut problems that may be related to a deficiency.
Read more: Fecal transplants: a new treatment for IBD
The role of external factors such as diet, drugs and pollution in IBD is complex. But medical science is making great strides in looking at the impact of environmental factors. “It’s pretty revolutionary the way the field opened up,” Meyer says.
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