If you go to the grocery store you'll probably notice that gluten-free products are more widespread than ever-everything from bread and pasta to chips and dessert have gluten-free versions. (Gluten is a protein primarily found in foods containing wheat, barley or rye.)

And that's for a good reason: roughly 18 million Americans have some degree of gluten sensitivity, according to Alessio Fasano, director of the University of Maryland Center for Celiac Research, and as many as 3 million Americans (about 1 percent of the population) have celiac disease.

For people with celiac disease, the battle in their gut between their immune system and the gluten winds up damaging tiny, fingerlike projections called villi that line the small intestine and absorb nutrients. The damage prevents nutrients from being absorbed properly, causing a variety of health problems.

Doctors are still not sure what actually causes celiac disease, an autoimmune disease that results in full-fledged gluten intolerance and can cause a host of digestive complications and other more serious health problems.

One Possible Cause

In recent years, at least four studies have indicated that a spring or summer birthday is associated with an increased risk of developing celiac disease. Granted, in some cases the risk was very small, but it's enough that some researchers are taking notice. One of the most recent studies, published in the Journal of Pediatrics in October 2012, looked at nearly 2,000 patients with diagnosed celiac disease. More were born in spring than any other season. "Clearly, no one model will explain all cases of celiac disease-it's a complicated problem," notes one of the study authors, Dr. Carlos Camargo of Massachusetts General Hospital for Children. "But we think that we have identified an important clue."

You're probably wondering what on earth the timing of your birth would have to do with developing celiac disease. It's actually not as far-fetched as it might seem. Babies usually begin eating foods containing gluten at around 6 months. Those born in the warmer months would initially be exposed to gluten in the winter, when viral infections like the flu are more common. Some researchers suspect that early exposure to viral infections may play a role in how our body responds to gluten.

The theory that environmental factors early in life play a role in developing an autoimmune disease isn't entirely new. Researchers have noticed a similar birth connection in people with other autoimmune diseases, such as type 1 diabetes, atopic dermatitis, autoimmune thyroid diseases and multiple sclerosis.

Sources of Gluten

Breads, cakes, pasta and cereals may be the most obvious sources of gluten, but the protein also finds its way into many ingredients commonly used in processed foods as stabilizers, emulsifiers and thickeners. Canned soups and stews often contain modified wheat starch and so do some medications. Beer and whiskey are distilled from wheat and other grains. Some brands of vinegar, soy sauce and even salad dressings contain gluten, so it's important to read ingredient lists closely.

If You Think You've Got a Problem with Gluten

Some common symptoms of celiac disease are gas, bloating, constipation and diarrhea. Beyond digestive problems, the disease is implicated in a huge list of symptoms, including arthritis, anemia, infertility and osteoporosis. If you think you might be gluten-sensitive or have celiac disease, schedule a visit with your doctor-but keep eating bread and pasta until your doctor tells you otherwise. That's because if you walk into your doctor's office after being on a gluten-free diet, it's more difficult to make a diagnosis. Sometimes even people who test negative for celiac disease-and have no observable damage to their intestines-can have sensitivity to gluten, which can cause symptoms similar to those of celiac disease or a wheat allergy.

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