Covid-19 may have indirectly accelerated mortality in certain causes of death including dementia and Alzheimer’s disease, with more deaths than usual in the early stage of the pandemic but fewer in more recent months, new analysis suggests.

Most leading causes of mortality, including liver disease, diabetes and old age, saw a similar proportion of deaths that were above the pre-pandemic average – known as “excess deaths” – in both 2020 and 2021.

But deaths due to dementia and Alzheimer’s disease showed a “notably different trend”, according to the Office for National Statistics (ONS).

From March to December 2020, deaths in England and Wales due to these causes were 9.7% higher than usual, with a total of 4,990 excess deaths.

By contrast, in 2021, deaths due to dementia and Alzheimer’s disease were 4,417 below average, representing a 6.7% decrease.

There was a “similar trend” in deaths due to prostate cancer, with 352 extra deaths from March to December 2020 (a 4.0% increase) followed by 312 deaths below average in 2021 (a 2.9% decrease).

The figures offer “cautious evidence that the indirect effects of the coronavirus pandemic may have accelerated mortality in certain causes of death, thereby causing deaths to be below average later in the pandemic,” the ONS said.

This could be an example of “mortality displacement”, which occurs when vulnerable people, such as the elderly or those with pre-existing medical conditions, die sooner than expected.

Because they are not dying in the following days, weeks or months when they would likely have died, this can lead to a lower-than-average period of mortality.

“Further investigation is required to understand this,” the ONS added.

The trend is not evident in other figures, with most causes of death seeing similar proportions of excess deaths in both periods.

For example, excess deaths due to “symptoms, signs and ill-defined conditions” – often linked to old age and frailty – remained high in both March-December 2020 and in 2021.

This was the leading cause of death with the highest number of excess deaths in England and Wales across the whole period from March 2020 to December 2021 (7,085 – a 30.6% increase).

It was driven by people aged 80 and over, among whom 7,123 excess deaths were registered – 34.4% above average.

Cirrhosis and other diseases of the liver had the second largest number of excess deaths across the same period, with 3,061 more deaths, up 20.4%.

Diabetes also saw an excess of 2,696 deaths, representing a 24.7% increase.

All figures for excess deaths were calculated by the ONS using an average for the five pre-pandemic years of 2015 to 2019.

David Thomas, head of policy at Alzheimer’s Research UK, described the figures as “heartbreaking” and a “stark reminder of the growing challenge we face in tackling dementia”.

He added: “The need for more investment in dementia research has never been greater. With sustained, increased funding, we can use the lessons learned during the pandemic as an opportunity to enhance research into the diseases that cause dementia.

“We’re calling for the Government to set up a dementia medicines taskforce to apply the same approach that delivered life-saving Covid-19 vaccines to bringing about the first life-changing treatments for people who desperately need them.”

When looking at the total number of deaths in England and Wales since the pandemic began, the ONS found that even when deaths due to Covid-19 were removed from the figures, the number of deaths was still above average in nine out of 22 months.

Six of these were the consecutive months of July to December 2021, when nearly 17,000 non-Covid excess deaths were registered.

Professor Sir David Spiegelhalter of Cambridge University said many of the 17,000 could be people “whose deaths from respiratory diseases were prevented in the previous winter, and then succumbing to other causes in the following autumn”.

“Deaths have been both brought forward by Covid, and also delayed by the measures against it,” he said.

There were 75,668 excess deaths in private homes in England and Wales from March 2020 to December 2021 – almost matching the 74,138 fewer deaths in hospital due to causes other than coronavirus.

This “suggests a change of place, rather than additional deaths”, Professor Spiegelhalter added.

“We can only hope that appropriate end-of-life care was available.”