How Long Can an Older Person Live With Dementia?

The average lifespan of a person diagnosed with dementia is 4.5 years; however, when the diagnosis comes before age 70, patients can live a decade or longer, according to WebMD. The median age of death for patients with dementia is 90 for women and 87 for men. The median age of diagnosis is 84 for women and 83 for men.

Dementia is the loss of ability to think, reason and remember. Alzheimer's disease is the most common cause of dementia, according to the National Institute on Aging. It affects an estimated 5 million Americans. The chances of developing Alzheimer's disease double every five years after age 65.

Alzheimer's disease begins a decade or more before changes are evident in the individual, as reported by the National Institute on Aging. Despite the fact that the patient is free of symptoms, significant changes occur in the brain. The neurons that carry messages in the brain become less effective at communication. Eventually they are unable to transmit messages and die. The damage eventually reaches the hippocampus and inhibits the brain's ability to store memories. By the end stage of Alzheimer's disease, the patient requires assistance with even the most basic activities of life.