It is a known fact that dementia is a terrible disease, but a new study shows that it is also a deadly one. 

The study, which was released by the National Center for Health Statistics, found that the average rate of Americans who died from dementia doubles in the past 20 years. The study specificially show that dementia caused 30 deaths per 100,000 patients in 2000, and it increased up to 66 deaths per 100,000 patients in 2017. Alzheimer's disease is the most common type of dementia and it is made up of at least 46 percent of dementia deaths in the past two years. 

Dementia is used to describe a group of conditions that affect memory, behavior and thinking. These conditions can interfere with the patient's daily life according to CDC or the Centers for Disease Control and Prevention. Those conditions include Lewy body dementia, Alzheimer's disease, vascular dementia and frontotemporal disorders, according to NIA or the National Institute on Aging. 

Now the real question is, why are there a lot of people dying from dementia?  It's likely due to a combination of factors, says David A. Merrill, MD, PhD, a neurologist and geriatric psychiatrist at Providence Saint John's Health Center in Santa Monica, Calif.

"There's a 'silver tsunami,'" he says. "People are living longer and into old age, and we know that age is the single largest non-modifiable risk factor for dementia."

Also, there is also more of an awareness of the disease among the medical community and people as a whole, Dr. Merrill says, even though the way that dementia is diagnosed hasn't changed. "It may be that dementia is being looked for more now than in the past," he says, leading to an uptick in numbers.

So how does it kill you? When dementia reached it final stage, the patient's brain tissue shrinks and they can no longer care for themselves nor communicate, the NIA says. After some time, this can lead to a series of deadly complications resulting from the disease,Dr. Merrill says. 

A lot of people with dementia have difficulty in swallowing, and they also acquire other eating problems. When a patient can no longer swallow properly, their food and drinks can end up in their lungs thus causing pneumonia, Dr. Merrill explains. When bacterial pneumonia does not get treated, it can spread throughout their body and it could lead to sepsis, a severe immune system reaction that is considered fatal. Also, a patient can become dehydrated or they could became malnourished because of their inability to eat or drink. 

Another serious illness is the flu, that can lead to death in patients with dementia. "People with advanced dementia aren't able to express through language the fact that they're feeling ill so there may be later detection of an illness," Dr. Merrill says. "When an illness is finally detected, it may be more progressed and take over the body to the extent that it wouldn't have if someone didn't have dementia."

Accidents such as falls can also be the cause of death for patients with dementia. "People with dementia tend to lose insight about their limitations and may still take risks that they wouldn't in the past, like forgetting that they can't walk without assistance," Dr. Merrill says. "And falls come with a risk of serious injury and death." In fact, accidents are the leading cause of unintentional injury deaths in people aged 65 or older, according to the CDC.