Researchers from the Johns Hopkins Children's Center examined the blood folate levels of more than 8,000 people with and without asthma and allergies who were enrolled in a large, national health registry.
They found that those with the lowest serum folate levels were 31% more likely to have test-verified allergy and 40% more likely to have wheeze than people with the highest levels. They also found them 16% more likely to have diagnosed asthma, although the asthma finding wasn't statistically significant.
Pediatric allergist and study researcher Elizabeth C. Matsui, MD, MHS, tells WebMD that the relationship appeared to be dose-dependent, meaning that the people with the highest blood folate levels had the lowest incidence of wheeze and allergies and the people with the lowest folate levels had the highest incidence.
But she warns that it is too soon to recommend that people take folic acid -- the synthetic form of folate used in supplements -- in an effort to reduce their risk for allergy and asthma or to treat symptoms.
"That would be premature," she says. "Our findings are a clear indication that folic acid may indeed help regulate immune response to allergens, and may reduce allergy and asthma symptoms. But we still need to figure out the exact mechanism behind it, and to do so we need studies to follow people receiving treatment with folic acid."
Few Are Folate Deficient
Less than 5% of Americans have so little folate in their blood that they are considered deficient in the B vitamin, Matsui says.
That's because since 1996, the U.S. government has required folic acid to be added to cereals, flours, pastas, rice, and other grain products in an effort to ensure that pregnant women get enough of the vitamin to protect against certain birth defects.
Folate is also abundant in leafy green vegetables like spinach and turnip greens, citrus fruits, dried beans, liver, and many other foods.
The people in the study who had the least folate in their blood were not deficient in the vitamin. Instead, they had what would be considered low-normal plasma folate levels, Matsui says.
Nevertheless, even after adjusting for known risk factors for asthma and allergy, people with the lowest blood folate levels had the highest odds of test-verified allergy, wheeze, and allergy-related IgE antibodies.
The study appears in the latest online issue of the Journal of Allergy & Clinical Immunology.
Allergies, Asthma, and Folic Acid
Allergist Cascya Charlot, MD, tells WebMD that the findings are intriguing enough to justify interventional studies that could determine if folic acid supplementation really does protect against asthma and allergies.
Charlot is medical director of Allergy and Asthma Care of Brooklyn.
"There may be something there," she says. "Now we need to see if treating people with folic acid will reduce symptoms."
The study is among the first to suggest that folic acid may protect against allergy and asthma, but several other studies -- also preliminary -- suggest that supplementation may promote allergic disease in some populations.
Last October, Duke University researchers reported that mice exposed to high levels of folate prior to birth had an increased risk for allergic disease early in life.
The researchers suggested that the dramatic increase in asthma over the last two decades may be at least partly related to efforts to increase supplementation among pregnant women.
Charlot says the seemingly conflicting findings highlight the need for more research.
"It looks like there is something here, but it is clear that we don't really understand what is going on," she says.