Probably a lot more than you think.
It is estimated that there are 3 million people in the US alone who have celiac Disease. Of that number, only about about 3% are diagnosed. How's this for comparison: celiac is more common that Crohn's disease, ulcerative colitis, multiple sclerosis (MS), parkinson's disease AND cystic fibrosis combined. So then why is it so underdiagnosed?
For starters, the list of symptoms is 250 and counting. My worst symptoms were headaches, fatigue and nausea. For someone else it may be mouth sores and joint pain; for another, fibromyalgia. The problem is that doctors aren't even testing for celiac in most patients because it is still considered by many to be "rare". But you know, rare is kind of self-fulfilling, isn't it? For a more exhaustive list of symptoms, check out www.celiac.org
And then there's the testing for celiac disease. If it's not administered correctly (again, the whole rare thing coming in to play), it's pretty unreliable. The truth is, no matter how sick I ever got, I would never have shown up on a standard issue celiac panel blood test. And that is why it takes an average of 11 years for a patient to be diagnosed with celiac after they begin to experience symptoms. I guess I should be happy it only took me 2 and a half, huh?
So, if you have some strange symptoms and no one can figure out what's up, ask your doc to do a simple celiac panel. It will only hurt a little.