New diagnosis up more than 7 percent every year for decades, new study finds
By Amy Ratner, Medical and Science News Analyst
When researchers count how many people have celiac disease, they look at two different numbers. One is the incidence of celiac disease, which tallies how many people are newly diagnosed each year. The other is prevalence, which measures how many people are living with celiac disease.
The best way to visualize the difference is to picture a bathtub where the speed of the running water is incidence and the pool of water in the tub is the prevalence, says Benjamin Lebwohl, MD, a study author and director of clinical research at the Celiac Disease Center at Columbia University.
The rate of new diagnosis of celiac disease has increased 7.5 percent every year for the past few decades throughout the industrialized Western world, a new study by Lebwohl and colleagues from Canada, China and Sweden found.
An analysis of 50 studies showed a consistent pattern of increasing incidence over time across geography, sex and age. However, the increase was higher in women and children and some geographic differences were found. Forty two studies from Europe, seven from North America and one from New Zealand were included in the analysis.
“Recognizing that we may be in the middle of an “epidemic” of celiac disease in these regions could help with pushing the urgency for funding research,” said Ed Liu, MD, director of the Colorado Center for Celiac Disease at Children’s Hospital Colorado, who was not involved in the study. Liu noted that study’s finding of increasing incidence aligns with work he and colleagues have done showing that incidence in children is on the rise.
In the United States, incidence of celiac disease increased an average of about 8 percent each year from 1950 to 2010 in the county that is home to the Mayo Clinic’s celiac disease center. All U.S. studies in the analysis were done by the Mayo Clinic.
“In part, the incidence of celiac disease has risen because of improved awareness of the disease and more accurate and less invasive diagnostic testing, for example blood testing,” said study author Gilaad Kaplan, MD, scientific director of Digestive Health Strategic Clinical Network, Alberta Health Services.
But incidence studies are a way of showing that increases are a real phenomenon, according to Liu. “They can provide the validation that it is not just a fad or simply something due to more [celiac disease] testing,” he said.
The prevalence of celiac disease is about 1 percent of the general population, including both diagnosed and undiagnosed cases. While increasing incidence does have an impact on prevalence, the new study did not measure prevalence, Lebwohl said.
When the results of studies where combined, women had an incidence rate more than double that of men. When pooled incidence was broken out by age, the rate for children was more than one and a half times that of adults.
Although previous studies have shown an increase in the incidence of celiac disease over time, none has evaluated the changes of patterns in geographic areas on a global scale, the study authors note.
“In the past few decades, the incidence of celiac disease has dramatically increased in many industrialized nations contributing to an increasing burden on society and healthcare systems,” the study says. Additionally, the burden to patients includes: the costs of the gluten-free diet, the only treatment currently available; the consequences of inadvertent gluten consumption; the increased risk of complications; and the psychological and social impact of following a strict diet.
The study notes that the development of more accurate and cost-effective blood tests for celiac disease in the 1990s is one reason incidence is increasing. This increased use of blood tests has resulted in more frequent referrals to gastroenterologists. For example, in Calgary, Canada, the incidence of pediatric celiac disease tripled after the implementation of antibody testing, the study says.
Changes in guidelines for diagnosis, including allowing children in Europe to be diagnosed without a biopsy based on certain clinical and genetic criteria, along with celiac disease blood tests that are positive at very high levels, are also cited as reasons for the increase. In Scotland 56 percent of children diagnosed in 2016 did not have a biopsy.
Additionally, physicians are more likely to consider celiac disease testing when symptoms are not gastrointestinal and considered non-classical, according to the study. Screening, which is testing of those who are apparently healthy and do not have symptoms, is occurring more often in at-risk patients. Finally, widespread familiarity with the gluten-free diet in the mainstream has led more patients to ask their primary care doctor to test them for celiac disease.
While all these factors have contributed to increasing diagnosis, gaps remain. The diagnosis rate in the United States is thought to be somewhere between 17 and 50 percent and many patients report going undiagnosed for years, particularly if their symptoms are not gastrointestinal. Some physicians resist testing when patients suggest it, especially if their symptoms are neurological.
A 2018 study found that celiac disease is “substantially underdiagnosed” and an effective method for detection of celiac disease is needed. A 2019 comprehensive overview of celiac disease found that while the condition is “undergoing a true ‘metamorphosis’ due to the steady increase in the number of diagnoses identified,” a number of patients remain undiagnosed. More than 20 percent of participants in Go Beyond Celiac, an online research database, report that they saw more than four doctors before finally being diagnosed.
The incidence study notes that adult screening shows a similar occurrence of celiac disease in men and women. Screening tests for celiac disease in people who do not have symptoms that might lead them to seek a diagnosis. The authors attribute the nearly double rate of diagnosis in women to the fact that they use healthcare services more than men. Also, some of the conditions associated with celiac disease are more commonly diagnosed in women, for example hypothyroidism.
Consequently, initial diagnosis of another disease may lead to a higher rate of detection of celiac disease in women. Researchers call for more studies to determine whether there are genuine differences in celiac disease based on sex or if celiac disease is simply under-diagnosed in men.
While improvements in diagnosis account for some of the rise in incidence, environmental factors are also most likely contributing, the study says.
High levels of gluten fed to infants, use of antibiotics in a child’s first year, early childhood infections, and less exposure to microbes early in life resulting in overactive immune responses late in life, are among proposed environmental factors the study noted.
Since genetics are not changing, the studies support the idea that the environment is changing and leading to rising autoimmunity, Liu noted. “People wonder if they are doing something ‘wrong’ that leads to their kids getting celiac disease,” he said. “We have no specific answers, but we note that this is a pretty ‘global’ event in the Western world.”
Meanwhile, incidence is stabilizing or decreasing in some parts of the world. For example, adult incidence in Finland decreased by more than 3 percent each year from 2005 to 2014 while childhood incidence stabilized from 2008 to 2013. In Sweden, onset of celiac disease in children stabilized from 2003 to 2009.
“Since these regions represent areas with some of the highest incidence of celiac disease, it is plausible celiac disease has reached peak incidence in these nations,” the authors write. The study points out that other gastrointestinal diseases, including inflammatory bowel disease, have stabilized or decreased in several industrialized countries.
However, it is possible that incidence is stabilizing in part because people are adopting the gluten-free diet without having been diagnosed with celiac disease. “With a proportion of those with celiac disease remaining undiagnosed…the true incidence of celiac disease is masked,” the study says.
Differences in reported incidences and the change of incidence over time in different countries could shed more light on the environmental factors that contribute to the development of celiac disease, said Marisa Stahl, MD, assistant professor of pediatrics with the Colorado Center for Celiac Disease. Stahl, who was not involved in the study, is the recipient of the Society for the Study of Celiac Disease/Beyond Celiac Early Career Investigator grant, which she is using to study children diagnosed with celiac disease through screening.
Researchers found a gap in research done to determine the incidence of celiac disease in countries outside of the Western world, the study says. They note that prevalence is estimated to be less than 1 percent in Asia, Africa and South America.
The study calls for population-based studies to determine the frequency and changing patterns of celiac disease in newly industrialized countries, the study concludes.
You can find more about the study here.