According to a new study by researchers in National Institutes of Health, an individual’s likelihood of having clinical signs of dementia increases with the number of different disease processes present in the brain.

Among their findings is the observation that the combination of Alzheimer’s disease and cerebral infarcts (strokes) is the most common mix of pathologies in the brains of people with dementia. The implication of these findings is that public health efforts to prevent and treat vascular disease could potentially reduce the occurrence of dementia, the researchers say in the paper.

The researchers used data from the Rush Memory and Aging Project—an ongoing study of 1,200 elderly volunteers who have agreed to be evaluated every year and to donate their brains upon death. The current study compared clinical and autopsy data on the first 141 participants who have died.

Annual physical and psychological exams showed that, while they were alive, 50 of the 141 had dementia. Upon death, a neuropathologist, who was unaware of the results of the clinical evaluation, analyzed each person’s brain. The autopsies showed that about 85 percent of the individuals had evidence of at least one chronic disease process, such as Alzheimer’s disease, strokes, Parkinson’s disease, hemorrhages, tumors, traumatic brain injury or others.

Comparison of the clinical and autopsy results showed that only 30 percent of people with signs of dementia had Alzheimer’s disease alone. By contrast, 42 percent of the people with dementia had Alzheimer’s disease with infarcts and 16 percent had Alzheimer’s disease with Parkinson’s disease (including two people with all three conditions).