Celiac disease is common but mostly goes undiagnosed, say Canadian nutrition researchers who studied the blood work of nearly 3,000 people.

For those with celiac disease, eating gluten triggers an immune reaction in the small intestine that, over time, causes signs of damage that can be measured in the blood. Symptoms such as abdominal pain, bloating, gas, diarrhea, anemia and weight loss can result.

Ahmed El-Sohemy, a professor of nutritional science at the University of Toronto, wanted to see whether celiac disease results in subpar nutrition because of poorer absorption of vitamins and minerals. Iron deficiency, for example, can cause fatigue; too little vitamin C can lead to bleeding gums; and a shortage of calcium and vitamin D can cause brittle bones.

But to find out, he needed Canadian data on the frequency of undiagnosed celiac disease.

To that end, El-Sohemy and his colleagues checked blood samples from more than 2,800 individuals in Toronto. One group had an average age of 23, and the other 45.

Findings consistent with other countries

Their results bore out findings from other countries, showing celiac disease occurs in about one per cent of the population, the researchers said in Friday's issue of the journal BMJ Open.

However, the vast majority of people who may have the disease don't even know it.

"The prevalence of it being undiagnosed is incredibly high: 90 per cent," El-Sohemy said in an interview with CBC News.

This too is consistent with what's been reported in other countries such as the U.S. and the U.K., the researchers said.

"What I guess was a little bit surprising is just how common [undiagnosis] still remains given that gluten-free started becoming popularized well over a decade ago," El-Sohemy said.

Info 'essential' for health care planning

Celiac disease has a strong genetic component. About 30 per cent of the population has the version of a gene needed to develop celiac disease, but that alone doesn't mean an individual will develop it, he said.

Estimating the frequency of celiac disease in the Canadian population is important, said Dr. Maria Ines Pinto Sanchez, a physician specialist in gastroenterology and nutrition at McMcaster University's celiac clinic. She was not involved in the study.

"This [study] will give us an idea of the magnitude of the problem in our country, and is essential for health care planning."

Studies in the U.S., Europe, Middle East, North Africa and South Asia also suggest about one per cent of people are positive for celiac disease based on blood tests for antibodies.

Gastroenterologists say diagnosing celiac disease can be difficult in part because symptoms such as fatigue are common in many other medical conditions.

There are two antibody tests to measure markers in the blood to evaluate someone for celiac disease.

Celiac disease is a genetic autoimmune disease in which people are unable to fully digest certain proteins from wheat. The partially digested products that remain trigger inflammation and can damage the lining of the small intestine. (Health Canada)

"It is very important to highlight that blood samples and biopsies to confirm celiac disease should be tested while the patient is consuming gluten, to prevent false negative results," Pinto Sanchez and clinic co-director Dr. Premysl Bercik said in an email. "A great proportion of the population is following a gluten-free diet even though celiac disease was not confirmed, which makes the diagnosis difficult."

A biopsy of the duodenum, the first section of the small intestine, is the gold standard to confirm the diagnosis.

False positives can occur, for instance, in people who have other autoimmune disorders, said Dr. Sheila Crowe, a Canadian professor of medicine working in the gastroenterology division at the University of California, San Diego.

"We call that latent celiac disease," Crowe said in an interview. "This study does not differentiate whether they have latent celiac disease or actually have celiac disease."

Nonetheless, Crowe called the study interesting and important for raising awareness.

Researchers will need to conduct studies in other provinces to clarify whether or not the findings are representative of the whole country.

El-Sohemy also points out that gluten-free foods are more expensive, and in some cases less nutritious, than their gluten-containing counterparts, and he worries that some people are spending money needlessly.

One potential conflict of interest in El-Sohemy's research is that he is the founder and chief scientific officer of Nutrigenomix Inc., which provides genetic testing for nutritional issues, including gluten intolerance.

The research was funded by the Canadian Institutes of Health Research.