Medical researcher Dr Hakkan Lai says young children are more affected by heat than adults. Photo: Supplied / Auckland Council
Caregivers are being warned to be aware of the risks that hot days can pose to children under five.
A study by medical researchers at the University of Auckland and others found that over a 20-year period, more young children needed hospital care when temperatures topped 24.1C.
Hospitalisations rose sharply with every added bit of heat, with dehydration, cardiovascular strain and inflammatory damage putting a strain on the youngest children, including newborn babies.
While the primary worries for parents on hot days might be avoiding sunburn, the researchers said children were going to hospital for more serious heat-linked conditions, with potentially lifelong implications.
The study's lead author, Dr Hakkan Lai, a senior research fellow in epidemiology and biostatistics at the University of Auckland, said pronounced effects on the number of hospitalisations were still evident three weeks after a hot spell.
"We can see hospital admissions increase from the first day of high temperature," he said.
He said young children were more affected by heat than adults for several reasons, including their faster metabolism, and their smaller bodies heating up faster.
Dr Lai said it was important for caregivers to be aware of the risks to children, particularly in places where the study found the highest impacts - including Central Otago, Central Canterbury and the East Coast, as well as densely populated areas.
According to the study, the rate of hospital admissions on hot days was worse among girls, the children of renters, and Pacific, Asian and Māori pre-schoolers.
Lai said the researchers were surprised to find such variation by ethnicity, location and housing status, which made the findings "very interesting."
Cold temperatures also caused hospital admissions in the study, however with New Zealand getting hotter, it is rising heat that is giving health researchers the greatest cause for concern.
The research team looked at daily maximum temperatures between 2000 and 2019 along with the causes of 647,000 hospital admissions for children under the age of five.
Over the seven years from 2012 to 2019, an estimated 290 preschoolers each year went to hospital suffering from heat-related conditions, they found.
They also modelled what rising heat would mean for hospitalisations as New Zealand's average temperatures increase because of fossil fuel emissions.
If New Zealand got 3C hotter, heat-linked hospitalisations of under-5s would more than quadruple to 1300 a year, they found.
Dr Lai said the link between heat stress and child hospitalisations was consistent with previous studies in the US and Australia.
Conditions linked to or worsened by heat in young children included infectious diseases, blood and immune disorders as well as diseases of the kidney, skin, and nervous system, he said.
As well as medical researchers at Auckland University, the study involved scientists from Waikato, Canterbury and Otago Universities.
The authors said rising temperatures also posed health risks for elderly people, however that was not the focus of this research.
New, more detailed climate projections recently released by the Government found New Zealand is set to get hotter, even faster than previously thought.
The latest projections by NIWA found if countries were slow to cut greenhouse gases, New Zealand could be 3C hotter by the end of the century than it was today.
Temperatures are already an average 1.1C hotter here than they were at the beginning of the 20th century.
Even if emissions plunge at the maximum pace which climate scientists deem viable, New Zealand will be 0.8C hotter by the end of the century than it is now, on top of the 1.1 heating the country has already experienced.
The authors of the latest study said it was important for paediatric services, healthcare and housing to be modified to moderate the effect of higher summer temperatures.
