WEDNESDAY, May 27 (HealthDay News) -- New British research provides more evidence that the bits of gunk in the brain known as plaques and tangles don't necessarily lead to Alzheimer's disease, as many experts have long believed.
In fact, the study found that many people over the age of 75 had signs of significant clogging in their brains but still managed to avoid senility.
The findings don't have immediate ramifications for the treatment of Alzheimer's disease, which remains incurable and only somewhat treatable. But in conjunction with other studies, they could redirect ongoing research, said Dr. Gary Kennedy, director of the division of geriatric psychiatry at Montefiore Medical Center in New York City.
"A lot of what is out there that's focusing on reducing the formation of amyloid plaques and tangles may just be off the mark," Kennedy said.
Amyloid plaques are globs of protein that form outside brain cells and stick together. Tangles are bits of protein that develop inside brain cells and create havoc of their own. Both have been linked to Alzheimer's disease.
In the new study, British researchers examined the brains of 456 people who had donated their bodies to science. The subjects were 69 to 103 years old when they died.
The findings appear in the May 28 issue of the New England Journal of Medicine.
The team found a strong link between clogging in the brain and Alzheimer's in 75-year-olds, but the connection lessened by the time people were 95.
In other words, plaques and tangles developed in very old people just as in their younger counterparts, but the very old weren't as likely to develop Alzheimer's.
The picture is not perfectly clear, however. "At all ages, there are some people who don't become demented before they died -- despite having a lot of plaques and tangles," said study co-author Dr. Paul Ince. "We do not know what would have happened if they had survived."
It's possible that Alzheimer's disease shortens life, so people who are susceptible to it simply don't make it into the older age group, reasoned Ince, a professor of neuropathology and head of the Academic Unit of Pathology at Sheffield University Medical School in the U.K.
Also, he added, the study suggests that people who become senile at a very old age may be affected by another factor -- shrinking of the brain.
As for future research, "we need to take account of the ability of some people's brains to withstand Alzheimer's better than others," he said. "If we knew why, it might help us with strategies to delay the onset of dementia."
For now, doctors are very limited in how they can treat Alzheimer's, Kennedy said. Medications can treat symptoms, much as painkillers help some people tolerate arthritis, but they don't cure the disease, he said.
And in many cases, the drugs simply don't work, he said.
To learn more, try the Alzheimer's Association.
SOURCES: Gary Kennedy, M.D., director, division of geriatric psychiatry, Montefiore Medical Center, New York City; Paul Ince, M.D., professor, neuropathology, and head, Academic Unit of Pathology, Sheffield University Medical School, U.K.; May 28, 2009, New England Journal of Medicine