NEW YORK — People with dementia had significantly greater risk of contracting the coronavirus, and they were much more likely to be hospitalised and die from it, than people without dementia, a new study of millions of medical records in the United States has found.

Their risk could not be entirely explained by characteristics common to people with dementia that are known risk factors for Covid-19: Old age, living in a nursing home and having conditions like obesity, asthma, diabetes and cardiovascular disease.

After researchers adjusted for those factors, Americans with dementia were still twice as likely to have gotten Covid-19 as of late last summer.

“It’s pretty convincing in suggesting that there’s something about dementia that makes you more vulnerable,” said Dr Kristine Yaffe, a professor of neurology and psychiatry at the University of California, San Francisco, who was not involved in the study.

The study found that Black people with dementia were nearly three times as likely as white people with dementia to become infected with the virus, a finding that experts said most likely reflected the fact that people of colour generally have been disproportionately harmed during the pandemic.

“This study highlights the need to protect patients with dementia, especially those who are Black,” the authors wrote.

Dr Maria Carrillo, chief science officer of the Alzheimer’s Association, which runs the journal that published the study, Alzheimer’s and Dementia, said in an interview, “One of the things that has come from this Covid-19 situation is that we should be pointing out these disparities.”

The study was led by researchers at Case Western Reserve University who analysed electronic health records of 61.9 million people age 18 and older in the United States from Feb 1 through Aug 21, 2020.

The data, collected by IBM Watson Health Explorys, came from 360 hospitals and 317,000 health care providers across all 50 states and represented one-fifth of the US population, the authors said.

Dr Rong Xu, a professor of biomedical informatics at Case Western and senior author of the study, said there had been speculation about whether people with dementia were more prone to infection and harm from Covid-19.

“We thought, ‘We have the data; we can just test this hypothesis,’” Dr Xu said.

The researchers found that out of 15,770 patients with Covid-19 in the records analysed, 810 of them also had dementia.

When the researchers adjusted for general demographic factors — age, sex and race — they found that people with dementia had more than three times the risk of getting Covid-19.

When they adjusted for Covid-specific risk factors like nursing home residency and underlying physical conditions, the gap closed somewhat, but people with dementia were still twice as likely to become infected.

Experts and the study authors said the reasons for this vulnerability might include cognitive and physiological factors.

“Folks with dementia are more dependent on those around them to do the safety stuff, to remember to wear a mask, to keep people away through social distancing,” said Dr Kenneth Langa, a professor of medicine at the University of Michigan, who was not involved in the study.

“There is the cognitive impairment and the fact that they are more socially at risk,” he said.

Dr Yaffe said there could also be a “frailty element” to people with dementia, including a lack of mobility and muscle tone, that could affect their resilience to infections.

Dr Carrillo noted that coronavirus infection was associated with an inflammatory response that has been shown to affect blood vessels and other aspects of the circulatory system. Many people with dementia already have vascular impairment, which may be compounded or amplified by Covid-19.

Indeed, the study authors subdivided patients by the type of dementia listed in the electronic records and found that people designated as having vascular dementia had a greater risk for infection than people designated as having Alzheimer’s disease or other types.

But Dr Langa and Dr Yaffe cautioned that there was significant overlap between types of dementia.

Many patients have both Alzheimer’s pathology and vascular pathology, they said, and physicians who are not specialists may not distinguish subtypes in providing codes for electronic records.

In examining the risk of hospitalisation and death for Covid-19 patients with dementia, the researchers did not adjust for demographics like age or whether they lived in nursing homes or had underlying medical conditions.

They found that Covid-19 patients with dementia were 2.6 times as likely to have been hospitalised during the first six months of the pandemic as those without dementia. They were 4.4 times as likely to die.

Black people with Covid-19 and dementia were significantly more likely to be hospitalised than white people who had both diseases. The authors did not find a significant difference in the mortality rate for Black and white coronavirus patients with dementia, although they wrote that the number of deaths analysed, 170, might be too small to provide a solid conclusion about that.

Experts noted that one limitation to the study was that researchers did not have access to socioeconomic information, which could provide increased understanding of patients’ risk factors.

Dr Langa also noted that the data reflected only people who have interacted with the health care system, so it doesn’t include “more isolated and poorer patients that have a harder time getting to doctors.”

Consequently, he said, the study may be “an underestimate of the greater Covid-19 infection risk for those with dementia.” THE NEW YORK TIMES