The prevalence of asthma has declined slightly among New Zealand youngsters, reversing a 30-year trend.
This mirrors reductions in Australia and Britain, but New Zealand children and adolescents still have one of the highest rates in the world.
Just over 22 per cent of children and nearly 27 per cent of adolescents reported wheezing in the preceding year, according to survey results from Auckland, the Bay of Plenty, Nelson and Christchurch.
The reductions of between one and three percentage points respectively from 1992 to 2003 may seem small, but are considered an important reversal.
"To summarise, the prevalence of asthma symptoms in New Zealand is mainly decreasing, which is good news," the researchers, Starship hospital respiratory paediatrician Professor Innes Asher and colleagues, report in yesterday's New Zealand Medical Journal.
Their findings contrast with a reported increase in the prevalence of symptoms from the 1960s to 2000.
They also found the severity of symptoms had decreased, but the reasons were not clear.
"Possible reasons for the observed decrease in symptom prevalence after a period of increase include a decrease in intensity of an aggravating environmental factor or a protective environmental/management factor. There may also be improved management of individuals with asthma," the paper says.
One theory is that the consumption of high levels of antioxidants - found in a healthy diet - may be linked with reduced asthma symptoms.
"However, there is currently no evidence that New Zealand children are in fact eating more healthily; rather there is increased concern about unhealthy diets."
But while prevalence of current symptoms had decreased, the percentage of youngsters who had ever had asthma increased - from 25 per cent to 30 per cent of children, and from 24 per cent to 32 per cent of adolescents.
This is attributed, tentatively, to increased awareness of asthma, and to misdiagnosis.
"There may be an increase in the labelling of asthma within preschool children who have viral-induced wheeze which has a good prognosis and which does not progress to the classical asthma phenotype in school-age children, or mislabelling of asthma earlier in life."
Has there been wheezing or whistling in the chest in the past year, defined as "current" symptoms?
Among children aged 6 or 7, it was "yes" for 23.6 per cent in 1992-93
* 22.2 per cent in 2001-03
* 29.7 per cent in 1992-93
* 26.7 per cent in 2001-03