Alzheimer’s disease may contribute to nearly as many deaths as heart disease and cancer, according to a new study, which found that deaths from the disease in the United States were much higher than reported.

According to a study published Wednesday in the journal Neurology, Alzheimer’s is playing a role in almost six times more deaths than officially recorded. These figures come from information gleaned from death certificates.

Study author Bryan D. James of the Rush University Medical Center in Chicago, said his team’s findings suggests that deaths from Alzheimer’s “far exceed” what is reported by the Centers for Disease Control and what is listed on death certificates.

“Knowing that almost as many people may die from Alzheimer’s disease as cancer and heart disease is a very eye opening piece of knowledge for the public, and for people who make funding decisions,” James told CTV News.

For the study, more than 2,500 people aged 65 and older were tested annually for Alzheimer’s. After an average of eight years, 1,090 study participants had died, and 559 participants who did not have dementia when the study began developed Alzheimer’s.

The disease was confirmed via autopsy in 90 per cent of patients who had been clinically diagnosed.

The researchers found that the death rate among study participants was four times higher after an Alzheimer’s diagnosis in subjects aged 75 to 84, and nearly three times higher in participants aged 85 and older. More than one-third of all deaths in those age groups were attributable to Alzheimer’s.

According to James, those figures would translate into about 503,000 deaths from Alzheimer’s among U.S. adults aged 75 and over in 2010. That’s nearly six times higher than the more than 83,000 reported Alzheimer’s deaths.

James said it is clear from the findings that Alzheimer’s disease and other forms of dementia are “under-reported” on death certificates and in medical records.

"Death certificates often list the immediate cause of death, such as pneumonia, rather than listing dementia as an underlying cause,” James said in a statement.

Caregiver Sharon Roszel’s father Roy died of dementia, but the official cause of death on his certificate was pneumonia.

“He got pneumonia because he had Alzheimer’s and he could not fight it,” Roszel told CTV News. “Alzheimer’s takes away everything, your ability to do a lot of things, and even to breathe.”

Meanwhile, Dr. Sandra Black, a neurologist at Toronto’s Sunnybrook Health Sciences, said dementia and Alzheimer’s weakens the body, leaving it open to infections.

“If you didn’t have dementia, you would probably not be dying, you would not be getting the pneumonia,” Black told CTV News.

James noted that attempts to identify a single cause of death fail to capture the true process of dying among the elderly, who often suffer from multiple health problems.

“Determining the true effects of dementia in this country is important for raising public awareness and identifying research priorities regarding this epidemic," James said.