Children who live further from the equator are more likely to develop food allergies and eczema because they receive less sunshine, a new study suggests.
A team of researchers from the Murdoch Children's Institute looked at data from more than 7,600 Australian children and assessed how rates of food allergy to peanuts and egg, eczema and asthma varied from Queensland to New South Wales down to Victoria and Tasmania.
Their findings were published in the latest edition of the Journal of Allergy and Clinical Immunology.
The study found that for children aged four to five, those in the southern parts of Australia were twice as likely to have eczema and 2½ times as likely to have an allergy to peanuts.
Among children aged eight to nine, the odds of having a peanut allergy were six times greater and the odds of having eczema were twice as great in the southernmost children when compared with those living in the north.
The study found no link between latitude and rates of asthma.
Lead researcher, Associate Professor Katie Allen, says the study suggests that sunlight might play a role in the increasing prevalence of food allergy and eczema.
"This study has further highlighted the possible link between food allergies, eczema and where you live. The results of our study provides further motivation for research into possible casual links into UV radiation and vitamin D levels in this disease group," she said.
"Investigating these links at a much finer level, by examining such things as temperature, levels of sunlight, as well as vitamin D in the blood, might provide more clues to the nature of these associations."
The research team said it was strongly placed to examine the link between vitamin D and the increase in allergic diseases. "It has among the highest prevalences of … food allergy, eczema, and asthma. It also has one of the longest north-south borders in the world, measuring approximately 4,500 kilometres from the North of Queensland to the South of Tasmania."
Although other food allergies, including cow's milk, soy, sesame and wheat, were assessed, these showed little evidence of a link to vitamin D, because they were triggered in different ways to peanut and egg allergies.
Dr Robyn Lucas, an associate professor at the Australian National University's College of Medicine, Biology and Environment, said that "one caution that perhaps is not brought out in the study is that we shouldn't leap straight from latitude to sun exposure and vitamin D.
"There are of course many things that vary by latitude – temperature, diet, exposure to infectious diseases.
"Although ultraviolet radiation varies by latitude, so does sun exposure behaviour, and it is really important to take account of that if you are suggesting a sun exposure or vitamin D causation. For example, it is really sunny in Darwin, with high UV levels, but may be so hot that people stay inside and so have low sun exposure, and even low vitamin D levels!"