The vitamin A added to cattle feed may protect against milk allergies, says a study from Vienna's University of Veterinary Medicine.

While uncommon in adults, an allergy to cow's milk is the most common food allergy in young children. According to the National Institutes of Health, 5 to 15 percent of infants show adverse reactions to cow's milk protein, such as lactose intolerance, and estimates of actual cow's milk protein allergy (CMPA) vary from 2 percent to 7.5 percent.

CMPA is different from lactose intolerance, in which a lack of the enzyme lactase results in the inability to properly break down lactose, a sugar found in milk products.

In the case of a milk allergy, the immune system itself reacts with a distinct immune response against the milk proteins. Specialized immune cells produce antibodies against the milk proteins and trigger an allergic reaction that has the potential of being much more dangerous.

The Viennese study found that the components of the cow's milk itself can help to prevent this reaction. The key is that the milk protein beta-lactoglobulin, a component of allergic reactions, can be neutralized by a metabolite of vitamin A called retinoic acid, turning a milk allergen into a milk tolerogen.

However, in order for this to happen, cows would have to receive an adequate supply of this vitamin through an abundance of green fodder, since researchers don't know if the same effect can be achieved through dietary supplements.

"Artificial supplementation of a diet with vitamins may not achieve the same effect as natural agents," said researcher Karin Hufnagl. "It is therefore necessary to supply vitamin A to an appropriate extent already during the keeping or feeding of the animals. This can be achieved, for example, by increasing the supply of green fodder."

An earlier study conducted by the University of Chicago and Italy's University of Naples found that probiotics eliminate cow's milk allergy in some infants. Infants fed a formula containing Lactobacillus rhamnosus GG (LGG), a specific type of probiotic found in many supplements, modulated the immune system's response to milk proteins, and allowed some babies to develop a tolerance for milk.

In addition, the probiotic also significantly changed the makeup of the babies' gut bacteria, producing higher levels of a bacteria that help maintain balance in the gut.