Editorials

Education and dementia

As long ago as the 2nd century BC poets and philosophers considered that an active mental life might forestall or delay the enfeeblement of old age.¹ In "De Senecute" Cicero suggested that old men preserved their intellects if they preserved their interests--"the use it or lose it" hypothesis.² In this week's journal a population based study reports that in elderly people a low level of education was associated with a higher prevalence of dementia, particularly Alzheimer's disease (p 970).³ In addition, several recent studies have indicated that education may protect against dementia.^{4 5 6 7} Bonaiuto et al found that the prevalence of Alzheimer's disease was 7.2% among illiterate people, 2.8% among those whose education had ceased at the fifth grade, and 0.5% among those who had studied in the fifth grade or over.⁵

Jorm suggested that people with high socioeconomic status might have a greater resistance to the effects of the dementing process, either because their better premorbid intellect reflected a higher level of neural reserve or because they tended to seek more stimulating environments, which helped to prevent a decline in cognitive skills.⁸ Other studies, however, found no link between education and the diagnosis of dementia,⁹ and the link between low social status and dementia may be due to a higher rate of vascular and secondary dementia in people from poor environments.¹⁰

If education does reduce the risk of dementia two mechanisms might explain the link. Education might in some way protect against neurodegeneration; or the onset of dementia might be delayed because education had improved neuronal networking so that when neurons died others could carry out similar functional tasks, so minimising signs of functional and cognitive impairment. Both of these mechanisms have strong practical implications.

In neurobiological research much debate has centred on whether the brain is more likely to degenerate as a result of overuse or underuse. Swaab argued that activation of nerve cells within the physiological range seemed to lead to the maintenance of neurones during aging and Alzheimer's disease, possibly by preferentially stimulating the action of protective mechanisms such as DNA repair.¹¹ He pointed to several studies showing that the brains of elderly rats exposed to an enriched environment had increased cortical thickness and weight and increased dendritic branching and that these rats' general performance was better than that of control rats from a non-stimulating environment. Dendritic growth continues in humans well into old age.¹² Nerve growth factor governs neuronal development, may play a part in Alzheimer's disease, and seems to be influenced by environmental change.¹³ Those links might partly explain the actions of education and continued mental activity in delaying the onset of Alzheimer's disease.^{14 15}

The evidence in support of the neuronal networking mechanism has been reviewed by Katzman, who noted that cognitive change in Alzheimer's disease is largely predicted by the density of neocortical synapses.¹⁶ He suggested that education could increase brain reserve by increasing the density of neocortical synapses, so delaying the onset of symptoms in Alzheimer's disease by up to five years. That delay would halve the prevalence of dementia in the better educated people. Katzman also argued that research on rats showed that both the brain weight in adults and the numbers of neuronal dendritic processes were associated with stimulation in early life.

If the onset of dementia is delayed by an increase in the brain reserve a person may die before developing symptoms.^{16 17} By contrast, head injuries (due to boxing, for example) may deplete the brain reserve and bring forward the onset of a dementia syndrome.¹⁸

Yesavage showed that stimulation programmes may be effective in reducing memory problems associated with normal aging.¹⁹ Psychological research has shown that elderly people have cognitive reserve capacity, which can be activated by simple training programmes.²⁰ Even without explicit training old people can increase their cognitive performance.²⁰ In other words, not only previous education but also continued mental activity may be important for elderly people. Adult education programmes and stimulating mental activity may help improve coping skills and strategies for solving problems, and in turn these may help offset the cognitive effects of normal aging and delay the clinical symptoms associated with Alzheimer's disease. Two recent studies in patients with dementia showed that mental stimulation programmes had beneficial effects on cognitive performance as assessed by standard tests.^{21 22} The follow up was short, but even temporary improvements in cognition may benefit both patients and their families.

The combination of good education and continuing mental activity may mean that people have to undergo more cognitive deterioration before dementia becomes clinically obvious or before their scores in psychological testing are in the range indicating impairment. If education has neuroprotective effects it may delay the onset of the pathological process. Even if the effects of education are not neuroprotective but merely induce better neuronal networking they will still delay the onset of the clinical syndrome while the underlying pathological process continues. The neuroprotective and neuronal networking mechanisms are not mutually exclusive and may interact. In practical terms, people with a high level of education who also have early dementia may have no well defined symptoms or signs, though their intellectual functioning could be adversely affected. This might be important if the sufferer had an intellectually demanding job or one that required a lot of new learning.

Delaying the onset of dementia will reduce its prevalence: fewer elderly people will develop a clinical picture of dementia during their lifetime. Alzheimer's disease and aging may be a continuum, with the prevalence of the disease continuing to rise in very old age.²³ The beneficial effects of education and mental stimulation may differ in different age groups. Further research is needed, but at present it seems prudent to recommend to elderly people that stimulating mental activity is worth while: there may be some truth in the saying "use it or lose it."

We thank Professor Al Hastorf, Professor Brian Cooper, and Dr Trevor Robbins for their comments.

Senior lecturer in psychiatry of the elderly Department of Psychiatry, University College London Medical School, London W1N 8AA

Lecturer Department of Psychiatry, University of Cambridge, Cambridge CB2 2QQ

Martin Orrell, Barbara Sahakian 

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