EPIDEMIOLOGY
pathways that lead to disease and identify new targets for treatments.17
Some factors in the environment have been linked to IBD. The ‘hygiene hypothesis’ has been suggested to explain why chronic diseases, with inappropriate immune system reactions (like IBD), occur in modern ‘cleaner’ environments. High levels of hygiene may reduce childhood exposure to bacteria and viruses and/or change the type of bacteria found in the gut. There are conflicting reports on childhood infections and whether they are a risk factor for IBD.18 Canadian researchers have found that children who had one or more prescriptions for an antibiotic in the first year of life are more likely to develop IBD.19 ex-smokers have a higher risk of CD, but not UC.20,30,14
Smokers and Because IBD is more common in
developed nations, air pollution has been investigated for a link to IBD. Certain pollutants were associated with an increased risk of development of IBD, but only in younger patients.21
Diet
may also be associated with IBD development, with high intake of total fat, polyunsaturated fatty acids, omega-6 fatty acids and red meat reported as increasing the risk.22 have had an appendectomy also have a lower occurrence of UC.23
an association with IBD does not necessarily imply causality. In other words, just because something occurs more or less frequently in people with IBD, it does not mean that this causes (or prevents) IBD.
IBD is more common in some ethnic groups, such as Jews of European descent,24,14
increasing in African Americans.28 or Asian origin.28,29
while
others appear to have a lower occurrence, such as aboriginal Canadians and New Zealand’s Maori.25,26,27
In the United States, Caucasians more often have IBD, but rates have been Rates remain comparatively low in Americans of Hispanic
In Canadian adults, there is a higher frequency of CD in women (1.3 females are affected for every 1 male).30,33
in urban settings than rural settings; there is no such association for CD.30
There is no gender difference in UC. Slightly more cases of UC are found By contrast, in
Canadian children, CD is more common than UC and boys are more commonly affected than girls 1.25 males affected for every 1 female.35
key findings:
• IBD is largely a disease of the developed world, with initially the emergence of UC in developing countries, and then the eventual predominance of CD, as a country becomes industrialized.
• Genetics is involved in IBD, shown by clustering within families and the identification of several genes which are more common in people with CD.
• Environmental factors are presumably involved in IBD, but it is not well understood how they influence the development of IBD.
• There is a higher frequency of CD in female adults in Canada, while boys are more commonly affected by IBD than girls in childhood.
People who It is important to note that
THE IMPACT OF INFLAMMATORY BOWEL DISEASE IN CANADA 28
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