MINNEAPOLIS -- Alzheimer's, known mostly for the memory loss and confusion it causes, may be the nation's third-most deadly killer, according to a study that suggests many more Americans die from the disease than is known.
As many as a half-million people in the U.S. are killed by Alzheimer's each year, or about five times more than the 83,494 now cited on death certificates, the research found. Many people fail to understand the destruction from Alzheimer's disease, which is fatal when it impairs parts of the brain that control basic functions like breathing and swallowing.
Heart disease and cancer remain the top U.S. killers. Alzheimer's, though, would replace respiratory disease as No. 3 based on the study results, up from No. 6. The findings should increase urgency to spend more on research on an illness that's becoming more common as the population ages, Bryan James, lead author and an epidemiologist at Rush University Medical Center in Chicago. It already costs more than $200 billion a year to care for patients with the disease, he said.
"We think Alzheimer's disease has been getting short shrift because it hasn't been considered a major killer, when it's really one of the top three in the country," James said.
The findings published in the journal Neurology also underscore the difficulty of identifying the ailments that cause people to die based on death certificates, which typically list only the immediate reason for the death, such as the heart stopping, James said. Some doctors may not know the patient's history and others overlook the dementia.
'Chain of Events'
"Everyone knows Alzheimer's disease is under-reported on death certificates," he said. "There may be a long chain of events between being diagnosed with Alzheimer's disease and dying years later of pneumonia."
James and his colleagues tracked two groups of people who enrolled in long-term studies and agreed to donate their brains after death. They noted who developed Alzheimer's and who didn't, and then compared death rates among the two groups.
None of the 2,566 volunteers ages 65 and older had dementia at the start, examining those enrolled in the Religious Orders Study and the Rush Memory and Aging Project. After an average of eight years, 559 patients developed Alzheimer's and 1,090 died. Patients with dementia were three to four times more likely to die than those who weren't diagnosed with Alzheimer's, and the median time from diagnosis to death was less than four years.
The researchers calculated the number of deaths that could be ascribed to Alzheimer's by comparing the number of expected deaths based on those without the disease to the number of people who actually did die after an Alzheimer's diagnosis.
"Deaths from all of the other major causes of death are going down over time and the only one going up is Alzheimer's disease," James said. "That's because we are coming up with effective treatments and preventions for other diseases and we have yet to do that for Alzheimer's disease."
It would take $20 billion over 10 years to make a significant difference in the effort to find ways to better diagnose, treat and prevent the disease, according to an expert advisory group convened by the Alzheimer's Association in 2012. The U.S. National Institutes of Health spent $503 million on Alzheimer's disease research in 2012.
"It is a progressive, fatal disease that causes brain cells to malfunction and die," said Maria Carrillo, vice president of medical and scientific relations at the Alzheimer's Association, in a statement. "It eventually takes away the ability to think, eat, talk, walk and care for oneself. Alzheimer's disease has no survivors."