Many years ago it was popularly believed that senility was a normal outcome of aging. Then, in the past few decades, many academics came to believe (hope?) that the brain did not decay all that much with aging, and that senility was the result of infrequent or preventable disease processes.
Those of us who know the glass is half-empty (and poisoned besides) never bought this obviously false hope. We of the dark and suspicious nature have long suspected that it was (by definition) abnormal to avoid brain decay, and those "sharp as a tack" 90 year olds represented very anomalous genes. Happily for we skeptics the data is increasingly supporting the depressing hypothesis that Alzheimer's is a "normal" consequence of aging that, like bad joints and bad hearts, very few will entirely avoid.
Not that denial is dead. Note below how the researchers and journalist confuse "normal" with "healthy" or "optimal". Bah. Weak muscles and flabby hearts are a normal part of aging. So are bad brains. If normal is what happens to most of us, and if most of us develop forgetfulness with aging, and most forgetfulness is due to Alzheimer's or vascular disease, then most of us (if we live long enough) will get Alzheimer's -- so Alzheimer's is "normal". What clearly does vary is the age of onset, not the common process.
Get used to it. If you don't like it, then support funding for research to slow the "normal" decay of the brain. (Not that I personally have anything at stake here.)
So read the article, but also appreciate the profound confusion afflicting both the journalists and (less forgiveably) the researchers. I've added a few comments to help out :-).
A new study refutes the notion that forgetfulness is a normal part of aging. Among elderly people who had mildly impaired thinking and memory before their deaths, autopsies revealed that more than three-fourths had Alzheimer's disease or small strokes. ...
... Researchers examined the brains of 180 elderly nuns, priests and brothers who had volunteered to undergo annual cognitive tests and to donate their brains after their deaths.
Of the 37 volunteers who had exhibited mild cognitive impairment, autopsies showed that more than three-fourths had suffered brain damage from Alzheimer's disease or stroke. Less than one-fourth showed no evidence of disease.
.. Everyone has memory lapses, such as forgetting a name. Mild cognitive impairment is more severe. A mildly impaired person might, for example, forget a conversation or read a story and remember only bits and pieces. However, the person would not have other symptoms of Alzheimer's, such as impaired judgment or reasoning. [jf: note the emphasis is on an inability to acquire new information.]
... There was one piece of good news in the Rush study. One-third of the participants showed no evidence of cognitive decline, even though their average age at death was 82. [jf: 2/3 had cognitive decline. That means it's "normal". but ...]
Surprisingly, autopsies revealed that about half of the people with no cognitive impairment had Alzheimer's disease. And nearly one in four had experienced strokes. Their brains apparently had a reserve capacity that enabled them to function normally despite damage done by disease, Bennett said. [jf: So even those who didn't have obvious cognitive decline still shared the same disease processes. They just weren't symptomatic yet. Might as well admit we're talking "normal" here.]