Rates of debilitating inflammatory bowel diseases (IBDs) such as Crohn’s disease among South Island children are up to three times higher than their North Island counterparts, the first New Zealand prevalence study has found. The University of Otago, Christchurch study was recently published in the IBD Journal, and provides the first snapshot of cases around the county.

The data, collected in 2015, showed between 40 and 60 children per 100,000 had a diagnosis of an IBD in the South Island. In the North Island, the rate was between 10 and 20 children per 100,000. The study surveyed children from all health board areas. In Canterbury, 40 children in every 100,000 had a diagnosis of IBD.

Researcher and paediatrician Professor Andrew Day said the difference between the islands was not fully understood, but could be due to variations in sunlight, and its impact on vitamin D levels. It warrants further investigation, he said.

"There is a growing incidence of IBD in children worldwide but little information about rates in New Zealand children. Our study found quite a striking difference between the North and South Islands. One theory we have for the difference is that South Island children could have lower levels of vitamin D. This has implications for their immune system as vitamin D is involved in the production of a molecule that plays a key defensive role in the gut."

Professor Day said the ‘vitamin D theory’ is supported by European research showing colder places such as Scandinavia had higher rates of the diseases than warmer countries on the continent.

The reason for an increasing number of children being diagnosed with IBD was a subject of intense debate and scrutiny internationally, Professor Day said. One theory was that children’s diet consists of far more processed than whole foods nowadays. Another was that children did not play outdoors as much and get exposure and immunity to germs, he said.

An IBD diagnosis was often a very big deal for a child and their family to deal with, Professor Day said.

"It’s a lifelong condition with no cure. For those with more severe forms of the disease, there are often hospital stays to administer medication or for surgery. Some children need to have regular injections or infusions of medication," Professor Day said.

Steroids used to be a common treatment for the condition but doctors were wary of prescribing them now because of better alternatives and steroids potential to affect growth, among other side-effects, he said.

"At diagnosis now we are commonly recommending a special liquid-only diet for a period of time, and later daily ongoing medication to maintain control of the condition."

Professor Day said his team hope to follow the prevalence study with one that measures vitamin D levels in IBD sufferers as well as their location in New Zealand.