"This is the first study to show that such markers of inflammation are raised long before clinical dementia appears," said coauthor Lenore J. Launer, Ph.D., of the National Institutes of Health. Researchers hope that such chemical signals can be used in the future to identify people who are at higher risk for dementia and who should receive therapies yet to be discovered.

Experimental studies have indicated that some type of inflammatory process occurs in the brains of people with Alzheimer's disease and people with vascular dementia. It is still unclear what role inflammation plays--whether it damages neurons directly or causes a cerebral angiopathy, which then leads to neuronal damage and loss.

In the current research, investigators identified 214 Japanese American men with dementia and 838 men without dementia, all of whom had been enrolled in the Honolulu Asia Aging Study, a project that began in the 1960s. When the men were middle-aged, blood samples were taken and stored. The current researchers examined the stored blood for evidence of high-sensitivity C-reactive protein.

The researchers found that men who had elevated levels of the protein in middle age had a three-fold increased risk for developing either Alzheimer's disease or vascular dementia in later life.

"Although the findings are consistent with the hypothesis that inflammation may be involved in the processes related to neurodegeneration, further research is needed to understand those mechanisms," said Launer.