Obesity among 4 year olds is continuing to decline, but one in three children are still considered overweight, a new University of Otago study shows.
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The results have been drawn from data from the Ministry of Health's B4 School Check - a free health and development check offered to 4-year-olds in New Zealand.
It is the second study of its type.
The first analysis of data collected from 2010 to 2016 and published in 2018, revealed a downward trend in the prevalence of obesity in 4-year-olds across all socio-economic and ethnic groups.
The latest study, undertaken by researchers from A Better Start National Science, at the University of Otago, and published in the International Journal of Obesity, saw the trend continue from 2017 to 2019.
Professor Barry Taylor from the University of Otago led the research which drew on the records of 55,000 children for each year of the study.
"They [results] suggest that across all sectors - so no matter what your socio-economic position, whatever ethnicity - rates of being an unhealthy weight are actually going down."
He told Morning Report that trying to determine why the trend is happening is complex but it is happening across the country suggesting "it is a whole society wide change instead of just some groups".
While the trend is also apparent in other countries it tends to be more patchy compared with the findings in New Zealand.
Professor Taylor also pointed out that the research does not measure the impact of the Covid-19 pandemic on obesity rates as it finished in 2019.
He said there is more awareness of the need for a healthy diet for children. With most children attending some form of pre-school education there are more guidelines offered to parents on what food is allowed.
"There are more changes occurring as well in society. I think probably the most important is likely to be a change in smoking, especially in pregnancy, which is going down and that has quite a strong effect I guess on nutrition and how babies gain weight."
The highest rates of childhood obesity usually occur in poorer households, however, the decline in the rate is more evident in this group, Professor Taylor said.
Some evidence points to obesity rates in older children still rising, he said.
However, the value of good nutrition and the dangers of smoking are being realised and it was a tribute to those working in the field.
"It is a whole society wide change instead of just some groups" Otago University Professor Barry Taylor
Researcher Dr Lisa Daniels said in the recent study, the percentage of children at or above the 85th, 95th and 97th percentile reduced by 5 percent, 3.5 percent, and 1 percent respectively between 2011 and 2019.
"What is really reassuring to see from this work is that the declines in high BMI [body mass index] over time are occurring overall and across sociodemographic indicators - sex, ethnicity, deprivation and urban/rural classification - suggesting a narrowing of inequities," she said.
Dr Lisa Daniels from the University of Otago was a member of the research team. Photo: Supplied / University of Otago
While the results are encouraging, the BMI of about 30 per cent of 4-year-olds would still be considered overweight or obese.
Dr Daniels observed that there was a lack of national data for children younger and older than 4 years.
She would like to see a focus on early preschool years "as this time point has been reported to be one of the critical life periods for the development of obesity and a target for early intervention and prevention".