As the UK endured record high temperatures of 40C this summer, there were around 3,000 more deaths in the over-65s than usual in England and Wales - the highest figure since 2004.
Many happened during the hottest days towards the end of July and in early August.
The data comes from a report by the Office for National Statistics (ONS) and UK Health Security Agency (UKHSA).
Experts say it shows just how dangerous hot weather can be.
"These estimates show clearly that high temperatures can lead to premature death for those who are vulnerable," said Isabel Oliver, chief scientific officer at the UKHSA.
"A warming climate means we must adapt to living safely with hotter summers in the future."
There were five heat-periods between June and August 2022 - defined as days when the average temperature is greater than 20°C in central England.
During those periods, there were 3,271 excess deaths - 6.2% above the five-year average - out of a total of 56,303 deaths in England and Wales.
And among those aged 65 years and over, there were 2,803 excess deaths - the highest number since 2004, when England introduced a plan to prepare for heatwaves.
The UK recorded temperatures of over 40C (104F) for the first time between 17 and 20 July, during one of the hottest summers on record.
The report also found:
- more excess deaths in women (2,159) compared with men (1,115)
- each heat-period was followed by a fall in deaths to below the average, suggesting deaths among the most vulnerable happened earlier than they would have done
- there were 1,458 excess deaths in over-65s from 8-17 August - the deadliest period of heat
The analysis of deaths was compiled by the ONS using information from death registrations. The UKHSA also used a statistical model to estimate excess mortality, excluding Covid-19, during heat-periods.
Sarah Caul, head of mortality analysis at the ONS, said: "During the UK summer of record-breaking temperatures, there was an increase in deaths.
"However, these spikes around the hottest days were followed by periods of below average mortality.
"This is likely to be a result of short-term mortality displacement, especially among older age groups, where people died a few days or weeks earlier than expected."
Most of those who died had dementia and Alzheimer's disease, making it the leading cause of excess deaths, the ONS said.
People in older age groups with these conditions are most at risk during periods of intense heat.
The 3,000 extra deaths seen during the hottest days only go a small way to explaining the high rates of deaths seen this summer, however.
In England and Wales, there were about 16,000 more deaths from June to August than we might expect based on previous summers.
During the winter months, there are still more deaths on most days than during a hot summer like 2022.
How hot was summer 2022?
It was the joint hottest summer in England, tied with 2018 in records going back to 1884, and the fourth warmest summer for the UK overall.
Temperatures in the UK rose above 40C for the first time - with a new record-high temperature of 40.3C being set at Coningsby, Lincolnshire.
33 other locations went past the UK's previous highest temperature of 38.7C, set in 2019.
New record-high temperatures were also set in Scotland and Wales in July - 34.8C and 37.1C respectively.