A study has found a clear link between a lack of vitamin D and the risk of developing asthma, highlighting the "dark side" of a lack of sun exposure.

Children with prolonged vitamin D deficiency in the first decade of life are more likely to develop asthma and allergies, according to a new study.

The study, published in the Journal of Allergy and Clinical Immunology, has found evidence of a clear link between a lack of vitamin D in early childhood and allergic disorders such as asthma and eczema.

It has also revealed a "dark side" to the highly successful anti-skin cancer messaging, says Professor Katie Allen, of the Murdoch Childrens Research Institute.

Vitamin D deficiency has been on the rise in developing countries because of increased indoor time and sun-avoidance measures.

The sun is the best natural source of vitamin D, which is known to be important for lung function, lung development and immune function.

New research shows just how important it is during childhood.

Researchers at the Telethon Kids Institute tracked vitamin D levels in a group of more than 260 Perth children at a high risk of asthma from birth to age 10.

The more times the kids recorded deficient levels of vitamin D, the more likely they were to have asthma, allergies and eczema at age 10, lead author Dr Elysia Hollams says.

Children with vitamin D deficiency at six months of age were also more likely to experience two conditions previously associated with heightened asthma risk: increased harmful bacteria in the upper airways and increased susceptibility to severe lower respiratory infections involving fever.

The findings raise the question of whether there should be increased vitamin D exposure through diet, Prof Allen says.

"Australia is one of the few developed countries that does not fortify its food supply with vitamin D and therefore it may not be a coincidence that we have the highest rates of allergic disease, including food allergies, in the developed world," Prof Allen said.

However, parents have been cautioned against rushing out and buying vitamin D supplements.

"We still don't know what the optimal level of vitamin D is for good lung health and immune function, and we don't know if supplementation would address this issue or if healthy sun exposure is what is required, given that vitamin D is an indirect measure of recent sun exposure," Dr Hollams said.

Study co-author Professor Prue Hart says in a country like Australia, where too much sun exposure can prove harmful, it is all about finding a "safe and sensible balance between exposure and need".