Children deficient in vitamin D at age one are more likely to have food allergies, Melbourne researchers have found - but only if their parents are born in Australia.
In a study of 5000 children, researchers from the Murdoch Childrens Research Institute found that one-year-olds with vitamin D deficiency were three times more likely to have a food allergy than those whose levels were sufficient.
Children with two or more allergies were 10 times more likely to have vitamin D deficiency, according to the study, published in the Journal of Allergy and Clinical Immunology.
Lead researcher Katie Allen said there was some evidence that vitamin D could play an important role in regulating a child's immune system in the first year of life. She said it was likely that reduced diversity of bacteria in the gut due to increased hygiene explained the current food allergy epidemic, with vitamin D and an infant's diet also crucial factors.
Vitamin D deficiency was linked to food allergy only in children of Australian-born parents, Professor Allen said, which could be because they may have more diverse gut microbes.
"I personally think the hygiene hypothesis is very critical, but in that context I think there's a second factor, which is vitamin D and what we eat in first year of life," she said.
"It's probably the two coming together at a critical moment in history which has driven this quite bizarre situation in the past 20 years where food allergies are on the rise."
Australia has one of the highest rates of food allergy in the world, affecting more than 10 per cent of infants.
Professor Allen said Australia also had one of the highest rates of vitamin D deficiency, and was one of the few countries that did not fortify foods with vitamin D or provide supplements to infants.
"This study provides the first direct evidence vitamin D sufficiency may be an important protective factor for food allergy in the first year of life. We're really excited by these results, because what this suggests is there may be a modifiable factor that we can actually change and do something about to turn back the tide in the food allergy epidemic."
Professor Allen said the next step was to conduct a trial to provide infants with either a vitamin D supplement or placebo in the first year of life, to see if vitamin D could protect against food allergies or possibly help in developing tolerance to certain foods.
Katie Eyres, whose four-year-old son Harry is allergic to nut, egg and sesame, said if vitamin D supplements could help Harry outgrow his allergies "it would change our lives".
"It would make travelling and eating out in restaurants easier, and allow him to go to birthday parties and join in with other kids eating the same foods."