New Answers for Bowel Disease Causes: Scientists are beginning to look beyond the human genome to the environment for causes of bowel disease. A small but growing number of studies now suggest that air pollutants may play a role in diseases of the gut. Image: Romana Klee/Flickr
At 22, Mark Rievaj had one major love: speed skating. Day and night he spent at the Calgary track, vying for a coveted position on Canada’s national team. He was having the best season of his amateur career when he noticed a small fissure on his anus.
“I was losing blood, not much, but a little bit every day,” Rievaj recalls.
For months, his doctors struggled to make a diagnosis as Rievaj’s iron levels – and energy – plummeted and his skating performance faltered. Finally, he learned that he had Crohn’s disease.
Worldwide, an estimated 5 million people suffer from Crohn’s or ulcerative colitis, diseases of the gastrointestinal tract collectively referred to as Inflammatory Bowel Diseases.
In recent years, scientists have identified genes that may account for as much as 25 percent of these diseases. But now they are beginning to look beyond the human genome to the environment for answers. A small but growing number of studies now suggest that air pollutants may play a role in diseases of the gut.
The impacts of air pollution on the lungs and the heart have been widely documented for decades. But until now, few researchers have paid attention to the gastrointestinal tract.
“We tend to think about air pollution in terms of lung health, but the GI tract is also being bathed in it continuously. Fine pollution particles are cleared from the respiratory tract by mucous that makes its way to the gut,” said Karen Madsen, a gastroenterological scientist from the University of Alberta in Edmonton.
Some evidence suggests inhaling fine particles, or soot, may disrupt the immune system and trigger inflammation in the gut by making it more permeable and altering its normal bacteria.
Tiny airborne particulates, which come mostly from fuel combustion, are a worldwide problem. In the United States, more than 44 million people live in areas that exceed federal health standards for fine particles, according to the American Lung Association.
Edmonton, the capital of Alberta, ranked as the Canadian city with the highest average annual levels of fine particulate matter in 2010, with levels similar to those of Chicago, almost three times its size. Forest fires, car exhaust and fuel for heating homes and businesses are major sources in Alberta.
In Rievaj’s native Canada, one-half of 1 percent of the population is thought to suffer from bowel diseases – the highest incidence of any country. There are likely many reasons for the high rate. Scientists in Canada, including Madsen and Rievaj’s own doctor, Dr. Gilaad Kaplan, a gastroenterologist at the University of Calgary in Alberta, are combing the environment for clues.
“Understanding the risk factors can help us to mitigate the risk and prevent people from getting the disease in the first place,” Kaplan said.
Yet “we’re still very early in our understanding of the role air pollution may play in gastrointestinal disease,” said Dr. Eric Benchimol, a pediatric gastroenterologist at Children’s Hospital of Eastern Ontario in Ottawa.
One study by Kaplan and colleagues found that people in the United Kingdom between the ages of 5 and 23 with higher exposure to nitrogen dioxide, a component of traffic exhaust, were more than twice as likely to develop Crohn’s disease as young people with less exposure. However, no association was found between newly diagnosed cases of bowel diseases as a whole and total levels of air pollution.
Also, a study of hospital admissions in Wisconsin found that high air pollution emissions were associated with a 40 percent increase in the rate of bowel disease hospitalizations in 2002. The authors accounted for carbon monoxide, sulfur dioxide, nitrous oxide, volatile organic chemicals and fine particulate matter.