Earlier this year, we posted about what causes children’s food allergies.

The main predictor seems to be family history of food allergies. In addition, even if no one in the family has food allergies, having a relative with asthma or eczema could make your child more likely to develop a food allergy. Also, having another type of allergy, to pollen for instance, makes it more likely that you will have food allergies. This indicates that something in  your genes might be triggering the reaction.

In addition to a clear genetic factor, scientists also know that environment plays a role. Children who grow up in crowded cities suffer from more food allergies than kids in rural areas.

But ultimately, scientists still don’t really understand what causes food allergies, or why some children (1 our of 4) seem to grow out of their allergies.

However, a new study out last month seems to bring us one step closer to determining how food allergies develop. And it seems to start in the womb.

This discovery really begins with some old knowledge. In the 1990s, researchers determined that some link existed between high vitamin D levels and allergies. But proving a correlation or causation was more difficult. And even if the link existed, the studies done would also have to rule out other lifestyle and environmental factors. In addition, the research would have be done over several years in order to conduct tests and understand what happens before and after allergies arise.

Earlier this year, a German University published the findings of just such a study. They selected over 1200 mothers and children who were already part of another long-term study. Using tests of the pregnant mothers’ blood and the children’s cord blood, they determined the levels of vitamin D in the womb. Combining this information with a survey that assessed children’s food allergies over several years, researchers determined that vitamin D did have a role to play. But maybe not the one you think!

Vitamin D is essential for bone health and can prevent rickets and even lower mortality in older women. Considering the important preventative role it plays, when blood work shows a vitamin D deficiency, it’s important to supplement. Women are particularly prone to having a vitamin D deficiency, so for many years now, pregnant women have been encouraged to take vitamin D and folic acid daily, especially women with darker skin who don’t produce as much vitamin D naturally from sunlight.

But this latest study found that mothers with a vitamin D deficiency had children with fewer food allergies! While it seems impossible that a bad thing could actually be a good thing, the researchers have evidence of the negative role vitamin D might play in the immune system. A particular type of cell called T-cells keep the immune system in check, making sure it doesn’t overreact. But when mothers had a high level of vitamin D, their children’s cord blood had lower levels of T-cells, indicating that the vitamin D might be suppressing their development.

While this doesn’t help children who currently have food allergies, expecting mothers should talk to their doctors before starting a supplementation regime, especially if there is a family history of allergies.

Learn more about food allergies and find out how respiratory and seasonal allergies can be connected to food allergies.