Falls and stumbles may not be among the warning signs for Alzheimer's disease yet, but a new study suggests they could be among the earliest signs of changes in the brain.

Researchers at Washington University in St. Louis followed 125 cognitively healthy older adults -- both with and without Alzheimer's -- for eight months. Participants were asked to keep a journal of how many times they fell during the study. In addition, participants had a PET scan of their brains analyzed to look for PiB, a substance that can indicate the presence of beta-amyloid plaques. Beta-amyloid plaques are considered a sign of Alzheimer's development in the brain.

Researchers found twice the risk of falls for people with higher levels of PiB on their scans.

The finding is significant because Alzheimer's specialists say that changes in the brain may take place a decade or more before people begin to show symptoms. Targeting patients earlier may enable doctors to put patients on Alzheimer's medications earlier -- and may give them a better chance at slowing down the disease's progression.

But scientists caution not to read too much into a fall. In some people, unsteadiness and falls can be caused by blood-pressure medication, arthritis and other issues.