Although about one in five adults in the United States claim they have a food allergy, only about one in 10 actually do, according to a study published last Friday in the medical journal JAMA Network Open.

That number is still troubling, for it suggests that almost 26 million Americans have a food allergy, which can be life threatening.

The study also found that less than half of American adults with an actual food allergy have had the allergy confirmed by a doctor’s diagnosis. Furthermore, only about a quarter of adults in the U.S. who are allergic to a food have a current prescription for injectable epinephrine, the medication that they need to have on hand should they experience a potentially fatal reaction — anaphylaxis — to the food.

“It is important to see a physician for appropriate testing and diagnosis before completely eliminating foods from the diet,” says Dr. Ruchi Gupta, the study’s lead author and a pediatric immunologist at Northwestern University, in a released statement.

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“If a food allergy is confirmed,” she adds, “understanding the management is also critical, including recognizing symptoms of anaphylaxis and how and when to use epinephrine.”

Distinguishing among symptoms

For the study, Gupta and her colleagues conducted telephone and internet surveys of 40,443 American adults between October 2015 and September 2016. The survey asked the respondents if they had a food allergy; it also asked them specific questions about symptoms.

To have a true allergy, the respondents had to cite at least one of the widely accepted symptoms, which include hives, swelling of the lip or tongue, difficulty swallowing, chest tightness, trouble breathing, vomiting, chest pain, rapid heartbeat and low blood pressure.

Respondents who described only an itchy mouth or gastrointestinal symptoms, such as diarrhea and cramps, were not considered to have a food allergy. Those symptoms are not indicative of the body’s immune system reacting to an allergen, the study’s authors explain.

Many people confuse food allergies with food intolerance, oral allergy syndrome and celiac disease, they add.

Key findings

Nineteen percent of the study’s respondents said in the survey that they were currently allergic to at least one food. Yet only 10.8 percent of them reported symptoms that were consistent with an actual food allergy.

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The most common food allergens were shellfish (affecting 7.2 million adults), milk (4.7 million); peanuts (4.5 million); tree nuts, such as walnuts (3 million); finned fish, such as tuna and salmon (2.2 million); eggs (2 million); wheat (2 million); soy (1.5 million); and sesame (0.5 million).

Food allergies were most common among women and among ethnic and racial minorities. Remarkably, about half of the respondents said they had developed their allergy during adulthood. That was particularly true of an allergy to shellfish.

The study also found that less than half (about 48 percent) of the respondents whose reported symptoms indicated they had a food allergy had received such a diagnosis from a doctor. And only 24 percent reported having a current epinephrine prescription.

Those numbers may explain why so many people with true food allergies end up in a hospital emergency department. Almost 40 percent of the survey’s respondents with food allergies reported that they had made one or more emergency visits to a hospital because of an allergic reaction, and almost 9 percent said they had made such a visit during the previous year.

The risk of going to the hospital was especially high among people allergic to sesame. Almost a third of the respondents with a sesame allergy said they had been to a hospital emergency department within the past year.

People with asthma were also at an increased risk of making a food allergy-related visit to a hospital emergency department, the study found. That is consistent with previous findings that have shown an association between asthma and an increased risk of anaphylaxis.

An increasing health concern

This study has several limitations, especially its reliance on participants self-reporting their symptoms.

Still, the findings support other recent national surveys that have found that food allergies affect more adults in the United States than previously believed. As Gupta and her colleagues point out in their paper, research also suggests that the rates of food-allergy related visits to emergency departments are increasing among both children and young adults.

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“We were surprised to find that adult-onset food allergies were so common,” Gupta said in the released statement. “More research is needed to understand why this is occurring and how we might prevent it.”

FMI: The study can be read in full at JAMA Open Network’s website.