A new study suggests about half a million elderly Americans died from Alzheimer's disease in 2010. a figure many times higher than previously believed.
The Centres for Disease Control and Prevention has estimated that approximately five million people are living with Alzheimer's disease in the US and 83 000 die from the condition each year. "Many people do not realise that Alzheimer's is a fatal disease," said lead author Bryan D. James of the Rush Alzheimer's Disease Centre in Chicago.
"Alzheimer's disease starts in the part of your brain that controls your memory and thinking but over years it spreads to the parts of your brain that control more basic functions such as breathing and swallowing," he told Reuters Health in an email.
Read: Short-term memory loss a predictor of Alzheimer's
Current national estimates
Current national estimates are based on death certificates, which tend to underestimate deaths from dementia, he and his colleagues write in Neurology.
They analyzed data from two existing studies that followed people age 65 and older from a starting point when they did not have Alzheimer's for an average of eight years, with annual checkups and brain donation in the case of death.
One study followed religious orders of nuns and priests and the other followed people in retirement communities and senior housing facilities. In total, the studies tracked 2 566 people. During the course of the two studies, 559 participants developed Alzheimer's disease and 1 090 participants died.
People diagnosed with Alzheimer's were more than three times as likely to die as those without it. The risk was more than four times as high among participants ages 75 to 84.
Applying these figures to US deaths in 2010, when the data in the two studies were collected, the authors estimate that about 500 000 people over age 75 died from Alzheimer's disease that year. "There's no doubt that if you have Alzheimer's disease, it increases mortality risk," said Dr James Leverenz of the Cleveland Clinic Lou Ruvo Centre for Brain Health in Ohio.
Dementia underlying reason
But although current national estimates for Alzheimer's deaths are definitely low, he's not sure the true number is as high as the one found in this study. "The two groups are pretty highly educated," said Leverenz, who was not involved in the new research. "They were in generally a little bit better health than the general population."That means people in these studies could have been less likely to die from heart disease or other conditions, so a higher proportion might have died from Alzheimer's, he explained.
One of the reasons it is so hard to estimate the number of deaths from Alzheimer's is that dementia can be the underlying reason for a number of immediate causes of death, Leverenz said. For instance, severe dementia can lead to problems swallowing, which leads to malnutrition, which can lead to pneumonia, the study authors write.
Death certificates tend to list the immediate cause of death, in this case pneumonia, and leave out dementia."Understanding the societal burden of Alzheimer's disease (AD) helps us to plan for the coming years and to set budget and research priorities," James said.
"Understanding that AD may contribute to almost as many deaths as the two leading killers in America, heart disease and cancer, is an eye-opening figure that may convince the public and policy makers that AD funding should be increased."
Read: How is Alzheimer’s disease treated?
One of the deadliest killers
In the study, participants lived an average of four years after an Alzheimer's diagnosis, but Leverenz said he has seen patients live with the condition for much longer – 10 or even 20 years for those with an earlier onset of disease.
"The ageing of the baby boomer population means more people living with Alzheimer's disease, which in turn means more people dying from Alzheimer's disease since no effective treatment or cure exists," James said."As the number of deaths attributable to Alzheimer's goes up, it could continue to move up the ranks of the deadliest killers in our nation."
A person-centred Approach to Alzheimer’s disease
Alzheimer's drugs may benefit heart
Alzheimer's treatment shock