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Predicting and Preventing Dementia

Adolescent boys who struggle to understand how basic machines work and young girls who have difficulty remembering words are at increased risk of developing dementia when they’re older, new research has found.

According to the longitudinal study published in The Journal of the American Medical Association, lower mechanical reasoning in adolescence in boys was associated with a 17% higher risk of having dementia when they were 70. With girls it was a lower memory for words in adolescence that increased the odds of developing the degenerative disease.

It has been known for some time that the smarter you are throughout life, even as a child the less likely it is that you will develop dementia. Not a guarantee of protection – just a general trend. It has to do with cognitive reserve, the US researchers explain.

“Based on the cognitive reserve hypothesis, high levels of cognitive functioning and reserve accumulated throughout the life course may protect against brain pathology and clinical manifestations of dementia,” they wrote.

This theory has been supported by a number of studies such as the Scottish Mental Health Survey that showed that lower mental ability at age 11 increased the risk of dementia down the track.

But what had been less well-defined was whether there were any particular aspects of intelligence in young people that were better predictors (or protectors) of dementia than others.

This study goes some way to addressing this. Researchers were able to link sociobehavioural data collected from high school children back in 1960 with Medicare claims data over 50 years later that identified those people who had been diagnosed with Alzheimer’s disease and related disorders.

Interestingly, poor adolescent performance in other areas of intelligence such as mathematics and visualisation were also associated with dementia but not nearly to the extent of mechanical reasoning and word memory.

So why is this so? The study authors say there are a few possible explanations. Maybe the poor performance in adolescence reflected poor brain development earlier in life, a risk factor for dementia. Or maybe these adolescents are more susceptible to neuropathology as they get older? Or maybe they are the adolescents who adopt poor health behaviours such as smoking and little exercise?

“Regardless of mechanism, our findings emphasise that early-life risk stretches across the life course,” they said.

And what can be done about it? That’s the million-dollar question. The researchers say the hope is if we know the at-risk group we can get aggressive with preventive management early.

“Efforts to promote cognitive reserve-building experiences and positive health behaviours throughout the life course may prevent or delay clinical symptoms of Alzheimer’s disease and related disorder.”

An accompanying editorial takes this concept a little further. Dr Tom Russ, a Scottish psychiatrist says interventional research has identified a number of factors that can potentially influence cognitive reserve. These include modifiable health factors, education, social support, positive affect, stimulating activities and/or novel experiences, and cognitive training.

As Dr Russ says, you can’t necessarily change all of these risk factors, and even the ones you can change may become less modifiable later in life. But as this study demonstrates, you may be able to work on a person’s cognitive reserve at different stages throughout their life to ultimately lower their risk of dementia.



  1. Huang AR, Strombotne KL, Horner EM, Lapham SJ, Adolescent Cognitive Aptitudes and Later-in-Life Alzheimer Disease and Related Disorders. JAMA Network Open [Internet]. 2018 Sep; 1(5): e181726. Available from: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2701735 doi:10.1001/jamanetworkopen.2018.1726.
  2. Russ TC, Intelligence, Cognitive Reserve, and Dementia: Time for Intervention? JAMA Network Open [Internet]. 2018 Sep; 1(5): e181724. Available from: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2701735 doi:10.1001/jamanetworkopen.2018.1724.