Closeup of doctor viewing brain scan images

The incidence of dementia in the United States has declined over recent decades. Yet falling numbers haven’t been matched by a decrease in dementia-related brain pathologies, a new study finds. Instead, improved cardiovascular health — and healthier brain vessels — may explain the change, researchers say.

Dementia rates in the United States declined by 30% between 2000 and 2016, McKnight’s Senior Living reported in November. In the current study, investigators examined the prevalence of postmortem neuropathologies in birth cohorts over 25 years. They looked for a wide variety of changes during this time period, including Alzheimer’s disease, the burden of amyloid pathology in the brain and signs of cardiovascular disease such as atherosclerosis.

Aside from a potential increase in tau tangles (another brain pathology linked to Alzheimer’s), there were few changes over time in neurodegenerative pathologies among the birth cohorts, the researchers found.

The study also showed that blood vessel pathologies trended markedly lower over time in the birth cohorts. This may indicate an association between cognitive health and improvements in several cardiovascular risk factors, the authors concluded.

The results suggest that the decrease in Alzheimer’s and dementia incidence is likely linked to improved ability to combat stubborn brain pathologies, they said.

“Any improvements over time in clinical dementia observed in cohorts are likely in part associated with improved resilience to pathology rather than reduced Alzheimer’s disease pathology,” they concluded.

Full findings were published in JAMA Neurology.

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