New research from the University of Nottingham has found a fourfold increase in the rate of diagnosed cases of celiac disease in the U.K. over the past two decades, according to Coeliac UK, the national charity for celiac disease. Still three quarters of people with celiac disease remain undiagnosed, the group said.

The National Institute of Health & Care Excellence (NICE) previously estimated that only 10-15% of those with celiac disease had been diagnosed, however, this latest research by Dr. Joe West from University of Nottingham, funded by Coeliac UK and CORE has shown that the level of diagnosis has increased to 24%.

Celiac disease is an autoimmune disease caused by intolerance to gluten. Left untreated it may lead to infertility, osteoporosis and small bowel cancer. One in 100 people in the U.K. have coeliac disease, with the prevalence rising to 1 in 10 for close family members.

The only treatment for celiac disease is a strict, lifelong gluten-free diet. Gluten is a protein found in wheat, barley and rye and, once diagnosed, people with celiac disease need to eliminate all gluten-containing foods and make sure they only eat gluten-free varieties.

Researchers identified the number of people diagnosed during the study period using the diagnostic codes for celiac disease recorded in the Clinical Practice Research Datalink (1990-2011).

This research, published by The American Journal of Gastroenterology comes out as the charity celebrates its annual Awareness campaign, which this year is titled the “Gluten-free Guarantee” and aims to improve availability of gluten-free foods in stores across the U.K.

Sarah Sleet, chief executive of Coeliac UK said: “This latest research shows that nearly a quarter of people with celiac disease have now been diagnosed and gives an up to date picture of the diagnosis levels across the U.K. Of course, increasing numbers with a diagnosis is good news and will inevitably mean that there will be an increased demand for gluten-free products in supermarkets. But the three quarters undiagnosed is around 500,000 people—a shocking statistic that needs urgent action.”

From May 12-18 2014 the charity is asking people across the U.K. to support the “Gluten-free Guarantee,” which asks supermarkets to commit to have in stock eight core items of gluten-free food, making it easier for people with the condition to manage their gluten-free diet, which is their only treatment.

“Can you imagine going into your local supermarket and there is no bread you can eat, not one loaf not one slice? And when you check out the pasta, cereal or flour again there is nothing available on the shelf, which means you have to trawl around two or three stores in order to be able to find your staple foods. This is not about your preferred brand but about the major supermarkets ensuring that they have sufficient stock in all their stores whatever their size for this growing market of people who depend on gluten-free food for their health.”

The symptoms of celiac disease range from mild to severe and can vary between individuals. Not everyone with celiac disease experiences gut related symptoms; any area of the body can be affected. Symptoms can include ongoing gut problems such as bloating, abdominal pain, nausea, constipation, diarrhea, and wind, and other common symptoms include extreme tiredness, anemia, headaches and mouth ulcers, weight loss (but not in all cases), skin problems, depression and joint or bone pain.