PET imaging with the radiotracer florbetapir (Amyvid, Eli Lilly) showed that the amount of beta amyloid in people's brains increased with age, and approximately 20% of adults age 60 or older had significantly elevated levels of beta amyloid.
Previous research has linked high amounts of beta amyloid to reduced memory, reasoning, and the ability to process information. The study was led by Karen Rodrigue, PhD, a postdoctoral fellow at the Center for Vital Longevity at the University of Texas at Dallas.
The study enrolled 137 people (82 women and 55 men) with a mean age of 64 years (range, 30 to 89 years) and a mean 16.4 years of education. Study participants showed no signs of dementia.
The participants were tested for the apolipoprotein E (APOE) gene, which has been linked to a higher risk of Alzheimer's disease. They were also evaluated on their ability to process tasks, reasoning, memory, and verbal acuity.
All subjects completed four two-hour visits, which included two sessions for cognitive and neurophysiological testing, followed by one day for an MRI scan and another day for PET beta-amyloid imaging. The participants received 10 mCi of florbetapir prior to the PET scan (ECAT HR, Siemens Healthcare) to determine the level of beta amyloid in eight cortical regions of the brain.
The analysis of PET scans revealed that beta-amyloid deposits were distributed differentially across the cortex, and progressed at varying rates with age across cortical brain regions. The amount of beta amyloid in the subjects' brains increased with age, and approximately 20% of adults age 60 or older had significantly elevated levels of beta amyloid.
In the group with higher levels of beta amyloid, 38% had the Alzheimer's risk allele of the APOE gene, compared with 15% of those who had lower levels of beta amyloid.
The 18 subjects with greater levels of beta amyloid showed decreasing cognitive performance for processing speed, working memory, and reasoning ability. However, the study found no "significant association" with episodic memory.
The results "indicate cognitive declines across many domains are linked to beta amyloid in adults who have apparently good cognitive health, suggesting detectable cognitive effects may occur even in the recently proposed preclinical phase of Alzheimer's disease," Rodrigue and colleagues concluded.
"A key question for future research is whether some adults with high levels of beta amyloid will maintain good mental function for a long period of time and whether higher beta-amyloid deposits in healthy adults always predetermines cognitive decline," said co-author Denise Park, PhD.