Vitamin D deficiency has been linked to a range of health issues from poor bone health to heart disease, diabetes and some cancers.
Now Australian researchers have found a new connection: children with vitamin D deficiency are at an increased risk of food allergies.
Allergy rates have massively increased over the past 20 years. In Australia, food allergies are of particular concern with studies finding one in 10 children under 12 months of age is affected.
In new research, a team led by Professor Katie Allen, paediatric gastroenterologist, allergist and researcher with Murdoch Children’s Research Institute (MCRI), found children deficient in vitamin D are three times more likely to have a food allergy. They are also more likely to have multiple food allergies.
“This study provides the first direct evidence that vitamin D sufficiency may be an important protective factor for food allergy in the first year of life; this adds supporting evidence for medical correction of low vitamin D levels,” Allen says.
The rise in food allergy runs parallel with increased prevalence of vitamin D deficiency in pregnancy (and in the community generally), but it’s not clear if this is a cause or if other factors occurring during the child’s first year of life are to blame.
Inadequate exposure to sunlight, rather than diet, is the most common cause of low vitamin D levels as vitamin D is present in only very low amounts in most foods.
The new findings are based on a study of more than 5000 children and confirm earlier research showing the further you live from the equator the more likely you are to have food allergy.
Interestingly, it appears the link between vitamin D and food allergy was found only in children whose parents were born in Australia, leading researchers to speculate that genetic factors, such as parents’ ethnicity, may also play a role.
All about the gut
People with food allergies have an immune system that tends to overreact to substances that would ordinarily be considered benign, such as a peanut.
Allen says vitamin D is integral to the development of a healthy immune system in early life.
“We think the vitamin D story is very important in making sure that the defences of the intestinal gut are trained properly in a healthy way,” Allen says.
But research conducted by Allen and her colleagues suggests vitamin D is just one of several factors involved in “an interplay between the microbes in the gut and the way the immune system adapts to what it is going to attack and what it’s going to accept”.
Development of healthy gut bacteria, through early exposure to microbes, infections and parasites, along with exposure to allergens through early infant feeding are believed to play a role.
“We think it is all tied together: your genetic risk; what bugs you’re carrying; and then what you do with your diet and sunlight exposure, in relation to vitamin D; and allergen exposure, in terms of early diet. It’s all about training your gut through these critical areas.”
Allen’s colleague, Associate Professor Mimi Tang has looked at links between exposure to bacteria and allergic illness in early life. In one study, she found infants exposed to a wide variety of microbial bacteria in the first seven days of life were less likely to have eczema when they were 12 months old.
“This research suggests that altering the mix and amount of bacteria in our guts in early life could be an effective approach to the prevention of eczema, especially for those with an increased risk of developing allergic disease,” Tang says.
Before birth, a baby’s gut is sterile. But during their first few days of life they develop essential gut bacteria. A number of factors affect this process including whether a baby was delivered vaginally or by Caesarean; if they were breastfed or fed on formula; what contact they had with parents, siblings and hospital staff; and whether they were given antibiotics.
While Tang’s not suggesting parents put newborn babies in the dirt to play, in her view allowing young children and older babies to play around in the dirt is probably not a bad thing.
Evidence has also found factors, such as having older siblings and pets, help reduce the risk of developing allergies.
Allen agrees: “We have evidence that dog ownership and a large family protect from egg allergies, and certainly also know it is something to do with the modern [urban] lifestyle as people who live in the country are less likely to have food allergies.”
Breastfeeding, solids and allergies
Feeding habits in the first year of life may also play a role in the development of allergic disease. Allen says some research suggests women should breastfeed for the first four months and continue to do so while introducing solid foods.
While some studies have suggested breastfeeding causes allergies, Allen says this is not really the case.
“Families with a history of allergies are more likely to breastfeed longer and their children are more likely to have allergies, but this is because of the family history, not the breastfeeding.”
Previously, some allergy experts recommended mothers feed babies only breast milk and no solid food for the first six months to reduce the child’s allergy risk. But evidence hasn’t backed this view either.
In fact, there’s some suggestion that there is a critical window around four to six months when it’s best to introduce foods, while continuing to breastfeed.
Allen’s research has found children who first eat egg during this ‘window’ are less likely to develop an allergy, whereas children first given egg after 12 months are at greater risk.
As for choosing to delay the introduction of certain foods known to cause allergies, such as eggs, peanuts, cow’s milk or fish, it actually may even increase the risk of them developing.
“There are now suggestions across the field of allergy research that allergen introduction is important to help induce and maintain tolerance [to certain allergenic foods],” Allen says.
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