Research has shown January 27 to be the most-deadly day for heat-related deaths.

There have been more than 4500 deaths caused by extreme heat events since 1900, more than the total of all other natural disasters combined.

General manager at Risk Frontiers Andrew Gissing, who has conducted research into heat-related deaths, said while the exact reason for why January 27 was the deadliest day for heat deaths was not known, there were several hypotheses.

"January is typically our hottest month," he said.

"It could be because there's more people being outdoors for long periods of time on Australia Day, but we just don't know why."

Mr Gissing said further work was under way to investigate heat-related deaths, with findings based on the past decade to be released later this year.

"Certainly in the past decade the big events have been a heatwave in Victoria and South Australia in 2009 and the heatwave in Victoria in 2014," he said.

"Without a doubt due to climate change we will be seeing more frequent heatwaves in the future."

According to Mr Gissing, people more at risk at dying due to extreme heat events were the elderly and those from a lower socioeconomic background.

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"Those with a lower socioeconomic status may find it more difficult to make their homes comfortable like with air-conditioning or insulation, or do other things to make their homes cooler," he said.

Cardiologist at the ANU Medical School, Arnagretta Hunter, said while she had seen fewer cases of heat-related illnesses this summer due to La Nina conditions, previous summers involved large spikes.

"Last year with smoke and the heat from the bushfires there were a lot of people in hospital, and it was similar the summer before," Dr Hunter said.