Sesame Allergies Are Likely More Widespread Than Previously Thought

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As an ingredient, sesame is pretty popular— it's in tahini and sushi; it's often mixed in granola, sprinkled on bagels or used as a flavoring in an array of dishes. But according to new research, this may be a problem for a substantial number of Americans.

While previous studies suggested sesame allergies affected about .2% of U.S. children and adults, new research published this week in JAMA Network Open estimates the number of sesame-allergic Americans could be as high as .49% — around 1.6 million people.

The study's findings come at a time when the FDA is considering adding sesame to its list of top allergens that must be noted on food packaging. Last October, then-commissioner Scott Gottlieb issued a request for information on the "prevalence and severity" of sesame allergies in the U.S. to aid in its decision.

Luckily, a team of researchers led by Dr. Ruchi Gupta, director of the Science and Outcomes of Allergy and Asthma Research Team at Northwestern Medicine Northwestern Medicine and a physician at Lurie Children's Hospital, already had data on hand — information from a national survey of food allergies they conducted between Oct. 1, 2015, and Sept. 31, 2016. For this study, researchers distributed surveys on food allergy diagnoses and symptoms to nearly 80,000 different people in over 50,000 households. To meet Gottlieb's request, all they had to do was pull out their sesame data and give it a look.

What they found: Of the nearly 80,000 people surveyed, about .49% reported having an allergy to sesame, an increase from previous estimates. Of these .49%, about two-thirds (.34% of the U.S. population) either received a diagnosis from a doctor or had allergic reactions that the researchers deemed convincing. Still, the overall findings suggest that sesame allergy is more widespread than previously thought. The researchers say they are confident that over a million people in the U.S. have sesame allergies, based on their data.

Additionally, notes Gupta's coauthor, epidemiologist Christopher Warren, about 1 in 3 people with convincing sesame allergies alone reported going to emergency rooms — a relatively higher proportion than previously thought. And people with sesame allergies were relatively unlikely to be diagnosed with them, compared with people who have other food allergies.

"It can be trickier to avoid sesame than other major allergens," he says, because it's often sprinkled on foods, added to dressings or added into condiments in small quantities. It's also not always labeled clearly.

Onyinye Iweala, assistant professor of medicine at the University of North Carolina division of rheumatology, allergy and immunology and a member of the UNC Food Allergy Initiative, calls the study "really important." She notes that its large sample size sets it apart from many previous food allergy studies, and increases her confidence in the findings.

"They were ... stringent in their definitions of food allergy," she says, though these definitions coexisted alongside the classic limitations of survey-based studies — the findings are dependent on people self-reporting their food allergies, and this may lead to under or over-reporting. However, she says the authors properly addressed their study's own limitations, and the overall finding is strong.

The researchers' paper comes at a time when food allergies in general are on the rise in kids in the U.S., according to the Centers for Disease Control and Prevention. Between 1999 and 2011, the prevalence of food allergies increased from 3.4% to 5.1%.

Even relative to this rise, however, Iweala says her peers in the food allergy world have been seeing a fair amount of sesame allergy among kids. (She personally has not seen an increase in her clinic, which cares primarily for adults). She says policymakers "should take note of these findings, since they put the prevalence of sesame allergy on par with the prevalence of some tree-nut allergies, like cashew or pistachio." However, she notes that regulators will have to weigh other factors, like logistics and costs of implementing new food allergy regulations.

Currently, the U.S. FDA requires food manufacturers to list the top eight most common food allergens on packaging: milk, eggs, fish, shellfish, tree nuts, peanuts, wheat and soybeans. The new findings on sesame allergy indicate its prevalence may rival that of previous estimates for some of these top 8 allergens, including some tree nuts.

Thomas Casale, chief medical adviser for operations at Food Allergy Research & Education (FARE), a nonprofit organization focusing on food allergy research, and a professor at the University of South Florida in Tampa, agrees the study is important and says policymakers should take note.

Sesame, he says, "absolutely should become the 9th" allergy listed on food packaging, given these findings. Sesame's absence from packaging could be contributing to a higher-than-usual level of dangerous allergic reactions reported by the study: "If you don't have any appropriate labeling, it makes it a lot more difficult for people to screen what they're eating."

On July 26, Illinois passed a law mandating sesame labeling on its food packaging. But because most packaged food crosses state borders, the impact of this law is yet to be seen, Gupta notes — it could run into challenges, or Illinois could push major food manufacturers towards what it sees as the right direction.

"It's going to be challenging," Gupta says. "But hopefully it's the first step for it to become a national law."

Susie Neilson is an intern on NPR's Science Desk. Follow her on Twitter here: @susieneilson.