NEW YORK (Reuters Health) - People with higher levels of the B-vitamin folate in their blood are less likely to have certain symptoms of allergic disease, a new analysis of US data shows.

"These findings suggest that dietary folic acid and factors affecting its metabolism might play an important role in the development and perpetuation of allergy and asthma," write the study's authors, Drs. Elizabeth C. Matsui and William Matsui of the Johns Hopkins School of Medicine in Baltimore.

There has been a sharp increase in the percentage of people in the developed world with allergies and asthma over the past couple of decades, the researchers note in the Journal of Allergy and Clinical Immunology. And in recent years, they add, levels of blood folate among US citizens have been rising due to fortification of grain products with the vitamin, initiated in 1998 to help prevent birth defects.

To investigate the possible role of blood folate levels in allergy, the researchers looked at 8,083 people 2 years and older participating in the 2005-2006 National Health and Nutrition Examination Survey.

The higher a person's folate levels, the lower their levels of immunoglobulin E, the antibody responsible for allergic reactions, the researchers found. People with higher folate levels also were less likely to have wheezing and atopy, or the tendency to develop allergies. While there also was a link between higher folate levels and a lower likelihood of having an asthma diagnosis, this relationship wasn't statistically significant.

Because the study was cross-sectional, meaning it only looked at a single point in time, the findings can't show whether high folate levels might prevent a person from becoming sensitized to allergens, prevent the development of allergy in already-sensitized individuals, or whether levels of the nutrient have any sort of causal relationship to allergy symptoms at all, the researchers say.

But the findings are in line with other research that has linked low levels of folate to a greater risk of inflammatory conditions such as heart disease and rheumatoid arthritis, they add.

They conclude: "Additional prospective studies will be required to lend insight to the potential role of folic acid supplementation in the primary prevention, treatment, or both of allergic diseases."

SOURCE: Journal of Allergy and Clinical Immunology, June 2008.