Why some people get dementia and others don’t
New findings on resilience to memory loss have been presented at the World Congress of Neurology, which is currently being held in Kyoto, Tokyo.
The US-based 90+ study has been looking at the mental health of the oldest of the old since 2003, enrolling over 1,700 participants over the age of 90 along the way. Data showed that around 40% of study participants had a dementia disease, with women over-represented in that group.
However, there was surprisingly little correlation between Alzheimer’s pathology – typically a buildup of amyloid-beta protein plaques and tau protein tangles in the brain – and dementia symptoms.
“Interestingly enough, autopsies revealed that about half of the oldest-old without dementia have a high degree of Alzheimer’s neuropathology in their brains although they were mentally fit while alive,” says Professor Kawas of the University of California, a lead researcher for the study.
At the same time, among participants who did develop symptoms of cognitive loss, around half did not have typical Alzheimer’s pathology.
The findings mirror those from the work of Professor Carol Brayne, a leading UK dementia researcher who runs a brain bank and dementia epidemiology program at the University of Cambridge.
Professor Brayne has also found very little correlation between the classic features of Alzheimer’s disease and beta-amyloid accumulation in post-mortems on people who were well characterised before they died.
These findings are clearly significant for any research program hoping to banish dementia by targeting Alzheimer’s pathology such as amyloid-beta accumulation in the brain. But it also prompts the question of why some people are cognitively resilient to Alzheimer’s pathology – which may have genetic origins – while others aren’t.
The 90+ study shows that at least some of the difference is attributable to lifestyle. Participants who were resilient to cognitive loss tended to exercise more, drink more coffee, and watch less television.
In a phenomenon known as cognitive reserve, higher levels of education seemed to protect against cognitive loss in people who were shown on PET scans to have amyloid plaque in the brain.
“People with a low level of education had a four times higher statistical risk of contracting dementia than those with a higher level of education. Among those without plaque, the educational difference was irrelevant,” says Professor Kawas.
The researchers also found that one of the best predictors of dementia was having multiple comorbidities.
“Multiple pathologies are at the root of dementias of all ages,” says Professor Kawas. “In the oldest-old, the presence of multiple pathologies is associated with increased likelihood of dementia. The number of pathologies also seems to be relevant for the severity of the cognitive decline. We will therefore need to target multiple pathologies to reduce the burden of dementia.”
Despite these advances in our knowledge of the causes of dementia, there remains great uncertainty over what preventive measures should be taken. The best evidence is for physical exercise, with studies showing that it can play a role in postponing or slowing age-related cognitive decline. High blood pressure in middle age has also been shown to be associated with later cognitive decline. And given the findings on cognitive reserve and dementia, cognitive training may also have an effect, but studies have yet to show this.
A new report acknowledges that more research needs to done on the efficacy of preventive measures, but suggests diabetes and anti-depression therapies, lipid-reducing drugs, initiatives to improve sleep quality and social involvement, and addition of folic acid to the diet along with other nutritional interventions may all be of benefit.
Access abstracts from the World Neurology Conference here.