1201 GMT January 21, 2018
A study of more than 1,700 people who lived into their 90s found the most resilient to the debilitating disease were also the most physically active, express.co.uk wrote.
Professor Claudia Kawas, a neurologist at California University, said,” Post mortems showed one-in-two dementia-free participants had Alzheimer's-style brain plaques when they died.
"Interestingly enough, autopsies revealed 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.
“On the other hand half of the dementia patients did develop symptoms of cognitive decline without these changes in the brain.
“The reasons for this ‘cognitive resilience’ — having Alzheimer pathologies while not showing symptoms — could be down to lifestyle.
“Those that showed most resilience got more exercise and watched less TV.”
The findings presented at the World Congress for Neurology in Kyoto, Japan, shed light on why some people get dementia and others do not — even if they reach a highly advanced age.
They follow Cambridge University research three years ago which found just one hour's exercise a week — such as jogging, football or walking — cuts the chance of Alzheimer's by almost half.
The 'The 90+ Study' is the largest of its kind and has visited participants in Orange County since 2003.
Neurological and neuropsychological tests are carried out every six months.
Earlier, this year research suggested more than a third of dementia cases might be avoided by tackling aspects of lifestyle including education, exercise, blood pressure and hearing,
Kawas said, "It's important to study the oldest-old. We can learn a lot from this fastest growing age group."
According to life expectancy projections most babies born since 2000 in countries with long life expectancies — such as the UK — will celebrate their 100th birthdays.
She said, "In view of the demographic developments delay of cognitive decline is crucial.
"We have calculated if interventions could delay the onset of Alzheimer's disease in those afflicted by two years there would be — in the US alone — nearly two million fewer cases than projected by 2050."
It turned out 40 percent of the participants had dementia diseases — with women being more heavily affected than men.
Education was particularly protective in individuals who were shown in PET (positron emission tomography) scans to have brain plaques — abnormal clusters of beta amyloid proteins — typical of Alzheimer's.
Kawas said, "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.
“But among those without the plaques the educational difference was irrelevant.
"Multiple brain pathologies are at the root of dementias at all ages.
"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.
“Major uncertainties continue to persist when it comes to the question of how dementias can be stopped or their progress delayed at all ages.
“An ongoing US study entitled 'Preventing Cognitive Decline and Dementia' failed to identify specific interventions.
"However, the overarching message we can derive from the findings so far is — keep your body and brain working in order to protect cognition."
Physical activity — or the lack thereof — was identified as one of the risk factors open to influence that has the greatest effect on cognitive disorders and dementia.
The study showed exercise can play a part in postponing or slowing down age-related cognitive decline.
Getting high blood pressure under control appears to be important for mental health as well — especially in mi-life between 35 and 65.
Even if decisive evidence has not yet been furnished there are increasing indications keeping high blood pressure in check can prevent or postpone dementia.
She said, "Interestingly while blood pressure control is generally an important preventive factor the picture is slightly different in the 90+ age group.
"In the oldest-olds there are indications higher blood pressure might even have a certain protective effect.
“There's currently no evidence of the efficacy of commercial computer-based brain training exercises.
“They appear to have only short-term effects and just in connection with the same tasks that are practiced over and over.
"People should be suitably informed about what they can do to prevent cognitive decline from the standpoint of today's scientific knowledge.
"The results of the report do not form a suitable basis for deriving public health strategies to counter the wide-spread disease of dementia.
"We need further studies to be able to better assess the effect of potential measures."
In England and Wales, it is estimated 1.2 million people will be living with dementia by 2040 — a 57 percent increase from 2016 figures.