A major new study bolsters the view that food allergies are among the nation's most common medical conditions, and researchers at the Johns Hopkins University and elsewhere believe the problem is growing.
The newly released study, perhaps the largest study of food allergies, showed that about 7.5 million people, or almost three in 100 people in the U.S., have a potentially life-threatening allergy to peanuts, dairy, eggs or shellfish. Children, as well as men and African-Americans, have higher rates.
"Food allergies are very real," said Dr. Robert Wood, director of pediatric allergy and immunology for Hopkins Children's Hospital and an investigator on the multicenter study. "It's among the most common chronic diseases in America. Food allergy has the real potential to cause dangerous or deadly reactions, so there needs to be more study and education."
The research, sponsored by the National Institutes of Health and conducted at Hopkins, among other institutions, was conducted to confirm earlier, smaller studies that have raised questions about the number of people sickened by what they eat.
The study was a conservative estimate, Wood said. It counted only those with severe allergies to four foods. It didn't count those allergic to other foods or with less severe allergies, or, more commonly, those who have digestive problems because they are intolerant to foods — meaning many millions more than those identified in this study must restrict their diets, sometimes in extreme ways.
Wood said that those highly allergic might have a dangerous reaction to a hamburger that was cooked on a grill at a fast-food restaurant where a cheeseburger had been cooked an hour before.
In the study, the most common allergy was to peanuts, with about 1.5 percent of people testing highly positive for the antibodies, proteins made by the immune system when faced with the allergens. About 1 percent were allergic to shrimp, 0.4 percent were allergic to eggs and 0.2 percent were allergic to milk. About 1.3 percent were allergic to more than one food.
Jake Meyrowitz is one of those allergic to milk. He's been allergic since birth, according to his mother Jessica Meyrowitz. The Bethesda mother had been supplementing breast milk with dairy-based formula and noticed he had a constant rash and gas and was rubbing his face on her as if he was itchy. Doctors came up with alternative theories, but Meyrowitz said she knew they weren't right.
She switched to soy formula and noticed a huge difference. An allergist tested Jake and confirmed the allergy. Later Meyrowitz would find out that he was also allergic to eggs, though now at age 8, he has mostly outgrown that.
Eliminating dairy and eggs from the household was no small task in the beginning, before labeling laws required manufacturers to list foods their products contain or may come in contact with. It was also before more people became aware of common food allergies, before peanut-free schools and before groceries carried foods designed for those with allergies as a matter of routine.
"It wasn't talked about eight years ago," Meyrowitz said. "Now I know tons of moms whose kids have allergies. ... This study confirmed what I already knew, and I'm not surprised. I think there may be more allergies, but really I think people just didn't know about it before, or they dismissed it."
Meyrowitz still has to control the food the family has in the house and everything Jake consumes, but it's more of a routine now. She's sure no one is missing out on anything. And she believes the whole family is more healthful because they eat fewer processed foods.
And as for milk, for the past year and a half Jake has participated in a study at Hopkins to try to treat the allergy with increasingly higher doses of milk protein to retrain his immune system. Meyrowitz said it's helping, and she worries less about Jake coming in contact with small amounts of milk.
Wood said there are several studies working on such treatments.
This latest research, published this month in the Journal of Allergy and Clinical Immunology, will be repeated in a few years to see if the prevalence of allergy is still rising, Wood said; past studies suggest it is. This study was based on blood samples and interviews with more than 8,200 people. They were ages 1 to older than 60 and participated in a large national study of various health matters by the NIH.
The study also confirmed links to asthma, eczema and hay fever. The food allergy, which generally surfaces in youth, likely precedes the other maladies and causes them, researchers said. The study also found higher prevalence in children, which is usually when the allergies develop. Kids can outgrow milk and egg allergies but don't usually outgrow peanut and shellfish allergies.
The study also found higher prevalence of allergies in boys than girls, although the numbers usually even out as the kids age. And the numbers were higher in African-Americans, as with asthma, although the reasons are not understood, Wood said.
There are dozens of theories about why people have grown more allergic to food. The processing may be a factor. But a more common theory is that Americans have cleaned too well and when the immune system is not exposed to germs and infectious agents, it will focus more on allergies.
But Wood said that theory has a major hole. There are lower rates of allergy in the Third World, which has a constant flow of germs, but there are higher rates in the inner city, also likely dirtier than the suburbs.
Another theory is vitamin D deficiency. The vitamin is produced by exposure to sunlight, and people have spent less time outdoors and use more sunscreen than they did 10 years to 20 years ago — about the same time food allergies began to increase.
A third theory suggests people have too much folate, a water-soluble B vitamin found in leafy green vegetables, among other food, in their diets. Women were advised to begin taking more folate during their child-bearing years about 20 years ago.
"It would be nice if these theories were true because they are fixable," Wood said. "But we just don't know."
Wood serves on the advisory board of the Food Allergy and Anaphylaxis Network, an advocacy and support group. The group says people are allergic to many more foods that the four in the study and offers tips for living with allergies.
The group says accounting for 90 percent of reactions are milk, eggs, peanuts, shellfish, tree nuts, wheat, soy and fish. An intolerance, such as to milk, doesn't involve the immune system, but it can cause digestive problems.
Jennifer Roeder, a spokeswoman for the group, said a doctor can help people determine if they have an allergy and a course of action by discussing symptoms and performing blood or skin tests. She said people should tell the doctor about all symptoms and timing related to foods. Keeping a log for a couple of weeks could help.
She said support groups can also help parents dealing with allergies.
"Whether you are new to food allergy or facing a new milestone in your child's life, meeting other families who are in the same situation and sharing experiences and support can be so helpful," she said. "More importantly, you understand that you are not alone."
Food allergies study
•About 3 in 100 Americans has a severe allergy to peanuts, milk, eggs or shellfish
•Children, African-Americans and men are more likely to have an allergy, though it's not clear why
•The prevalence appears to be growing and there are many theories as to why, including too much folate, too little vitamin D and too few germs for the immune system to focus on
An earlier version misstated the number of Americans with a severe allergy to peanuts, milk, eggs or shellfish. The Baltimore Sun regrets the error.