Asthma has plagued Zarika Lutske since the Northland girl was rushed to the intensive care unit as an infant, seven years ago.

But her mum, Nossie, says her wheezing all but vanishes when the family gets out into the wild.

"When we do bush walks, she tends to breathe normally - there are no signs of a wheezy chest at all."

Now a study of almost 50,000 Kiwi kids, published today in the international journal Nature Plants, offers evidence to back up the notion that green is good for our youngest asthma sufferers.

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While plants and trees are often thought of as triggers for asthma, the Massey University-led research suggested exposure to green natural environments - especially those with a diverse mix of vegetation - could protect against the condition.

Dr Geoffrey Donovan and Professor Jeroen Douwes used linked health data available through Statistics New Zealand's Integrated Data Infrastructure (IDI), and looked at links between the natural environment and asthma in 49,956 kids born since 1998.

The researchers, who followed the children until they were 18, used satellite imagery and land-use data to assess their lifetime exposure to the natural environment and vegetation types.

They found children who lived in greener areas were less likely to be asthmatic - and if they were exposed to a broader range of plants, they were even less likely to have asthma.

"There's considerable interest in understanding how exposure to the natural environment may protect against asthma, and in identifying what specific aspects provide the most protection," Douwes said.

"It's a chronic health condition affecting 334 million people worldwide, and its prevalence is increasing. While treatment has improved, it's not effective for all asthmatics, and there is no cure."

Other findings were consistent with previous research.

"We found that girls are less likely to have asthma than boys," he said.

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"Asian and Māori children had higher rates of asthma than Europeans."

Underweight or prematurely born children, the number of antibiotic prescriptions, and having a mother who didn't receive any secondary school qualifications and/or smoked also increased the risk of asthma.

In contrast, having siblings was protective.

"We hypothesise that the protective effects of exposure to green space and a more biodiverse environment are mediated by increased microbial exposure and gut microbial diversity, which in turn, promotes healthy immune responses and a reduced risk of allergies and asthma," Douwes said.

"Our finding that antibiotics, which are known to reduce gut microbial diversity, increase the risk of asthma, points towards the same underlying mechanism.

"Reduced stress and increased physical activity, associated with living close to green space, may be another reason for the observed protective effects."

While native New Zealand plants appear to be protective, exposure to gorse and exotic conifers was a risk factor for childhood asthma, which may be due to the low biodiversity of these land-cover types.

This was the first study of its kind in New Zealand, and one of only a few longitudinal studies internationally.

"Going forward, this research could help inform the design of public health interventions to reduce the global burden of childhood asthma."

Further experimental and observational research could focus on the specific biological mechanisms underlying the protective effects on childhood asthma.

"We are keen to study gut microbes and the immune system in families living close to diverse green space and compare them with families who do not live near green space, but are otherwise very similar."

Nossie Lutske, meanwhile, said she was always keen to hear about such discoveries.

"Whatever can help my daughter's wheezing ... I'll be the first in line to learn about it."