Introduction

Scientists have learned a lot about the way Alzheimer's disease and other forms of dementia develop. It's generally accepted that one of the later steps is accumulation of a substance called beta-amyloid peptide, which can be seen as microscopic deposits in the brains of Alzheimer's patients. Meanwhile, an important new study has shown that doing leisure activities that exercise the brain (e.g. card playing, crossword puzzles) in late life can protect against dementia.¹ Professor Joe Coyle of Harvard, writing in the New England Journal of Medicine, has tried to explain how brain- degenerative brain stimulating activities may influence the development of dementia.

Genes or environment?

First, Professor Coyle points out that most of our knowledge about the role of beta-amyloid peptide comes from studies on the brains of people who had a relatively rare form of the disease, based on their genetic make-up. Whether the results are valid for all other forms of Alzheimer's is uncertain.

Second, in late-onset Alzheimer's, which is much more common, it's known that both genetic and environmental factors play a role in it's causation; for instance, high educational achievement, independent of social class, has a distinct protective effect on dementia.

The latest study

Older people with many social contacts and who take part in various leisure activities may postpone the onset of dementia. But is it possible that people with very early dementia - i.e. hardly detectable - may, in fact, drop out of social activities, as part of their condition? The new study shows this isn't the case. It was begun in 75- to 85-year-olds who had been very carefully screened to exclude those with any possible early signs of dementia, and who were followed for an average of more than 5 years. And strikingly, a protective effect was only seen in people undertaking activities that required a mental effort - playing cards, board games, reading, playing a musical instrument, or doing ballroom dancing. In this study, there was no protective effect from physical activities (although some studies have reported otherwise - see link below).

How big is the effect of continued mental exercise? In the latest study, which signed up people aged 75 to 85, 28% of those who played games 'rarely' had developed dementia after 5 years, compared with 14% of those who played games 'frequently'. After 10 years' observation, 54% of 'rare players' had dementia, compared with 35% of 'frequent players'. And at 15 years, dementia was seen in 84% of 'rare players' vs. 60% of 'frequent players'.

How does mental activity help prevent dementia?

It's much harder to find an explanation of how mental effort can produce these results. There is speculation that building up intellectual resources (as by game-playing) can create a 'cognitive reserve'. This means the brain can buffer the initial damage by the disease process to the nervous tissues. It's more attractive to believe that mental activity can strengthen existing connections between nerve cells (called synapses), create new ones, and even stimulate the development of new nerve cells - something that until a few years ago was regarded as impossible.

One also has to find an explanation that can account for the famous Nun Study. In this, the spiritual diaries of nuns written in early adulthood were rated for the complexity of their sentence construction. It was found that the more complex their sentence structure as young nuns, the less likely they were to develop dementia. In other words, there may well be changes in mental processing that predates dementia by several decades.

Conclusions

One must deduce that very early influences (genetic make-up and early education) help create the brain set of connections that may ultimately allow, or avoid, dementia in later life. Assuming that the 75-year-olds in the recent study all started level in this respect - something the investigators were at great pains to try to secure - the results obtained are sufficiently clear that, in Professor Coyle's words, ". . . seniors should be encouraged to read, play board games, and go ballroom dancing, because these activities, at the very least, enhance their quality of life, and they just might do more than that".