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As More People Live Longer Why Are Rates of Dementia Falling?

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There is nothing quite as difficult to predict as the future. In my lifetime I have already lived through an "inevitable" ice age that never materialized and "inevitable" mass starvation (through overpopulation) that also never happened. When I was in Central America I remember reading a book called Inevitable Revolutions by the historian Walter LaFeber, but more than a quarter of a century later the inevitable still had not taken place. By now, according to predictions, most of us should have been dead from AIDS, that is if variant Creutzfeldt-Jakob Disease or Ebola virus had not got us first. The repeated failure of confident predictions is therefore almost enough to make one sceptical of dire visions of the future. Only the sheer pleasure of contemplating catastrophe to come keeps the market for apocalypses alive.

One of our present concerns in the western world is the rapid aging of the population. Never have so many people lived to so ripe an old age, and this at a time when the birth rate is falling. Who is going to support the doddering old fools who will soon be more numerous than the energetic and productive young?

A recent article in the New England Journal of Medicine points out that something unexpected has happened to confound the gloomy prognostications of epidemiologists and demographers. As the percentage of people surviving into old age increases, so the proportion of them who suffer from dementia decreases. People are not only living longer, but living better. This is a phenomenon that has happened across the western world.

The article states that “in 1993, 12.2% of surveyed adults 70 years of age or older [in America] had cognitive impairment, as compared with 8.7% in 2002.” Similar results have been obtained elsewhere. In the light of this unexpected and unpredicted trend, estimates of the prevalence of dementia in England have had to be revised downwards by 24 percent. The burden of the elderly on the economy will therefore not be as great as was feared.

What accounts for the decline in the prevalence of dementia?

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The explanation favored by the authors is first that the general level of education of the population has increased and second that the prevalence of risk factors for the development of small blood vessel disease, which causes dementia, has declined. Old people have healthier lifestyles and do more exercise than they used to. The decline in smoking (oddly enough once thought to be protective against dementia, but now thought to promote it) may have had a marked effect.

The authors do not tell us why or how education should be a protective effect against dementia. Are neurons like muscles that atrophy if not used? Surveys have repeatedly shown that the educated are less susceptible to dementia than the uneducated, though we must always remember that statistical association is not causation.

However, pessimists need not despair, as there are grounds for thinking that improvement may not last. The authors warn that the huge increase in obesity and type II diabetes may reverse the trend. The fatties of today will be the dements of tomorrow, or at least of the day after tomorrow. That is, of course, if no treatment is discovered in the meantime that cures type II diabetes or prevents its deleterious effects, so that people will be able to have their cake and not suffer the consequences.

Then, of course, there is the question of the level of education. Is it rising or falling? I can’t help feeling that all those screens that young people spend most of their days playing with send out invisible rays that cause their brain to atrophy.

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images courtesy shutterstock / altafulla / Kzenon