Is there a Flynn effect for dementia?

It seems so:

A new study has found that dementia rates among people 65 and older in England and Wales have plummeted by 25 percent over the past two decades, to 6.2 percent from 8.3 percent, the strongest evidence yet of a trend some experts had hoped would materialize.

Another recent study, conducted in Denmark, found that people in their 90s who were given a standard test of mental ability in 2010 scored substantially better than people who reached their 90s a decade earlier. Nearly one-quarter of those assessed in 2010 scored at the highest level, a rate twice that of those tested in 1998. The percentage severely impaired fell to 17 percent from 22 percent.

From Gina Kolata, there is more here.


>>>to 6.2 percent from 8.3 percent<<<

And what's the error bar on measurement, reporting, shifting criterion of diagnosis etc. Have no related disorders been invented over the last 20 years that may re-classify some erstwhile dementia patients into new bins?

Have no related disorders been invented over the last 20 years that may re-classify some erstwhile dementia patients into new bins?

I believe they used the same diagnostic criteria for both sets of people.

If they did then all they're doing is committing a bunch of errors and hoping both groups have the same rate of misdiagnosis. Today the diagnostic criteria for diagnosing Alzheimer's include biomarkers not known twenty years ago.

The study looked at the overall incidence of dementia, a broad diagnostic category, and not Alzheimer's specifically. Our increasing ability to parse out different variations of dementia with greater diagnostic certainty is a separate issue.

I'm deeply skeptical it could be Flynn effect. The causes of dementia are still poorly understood, but the etiology of the main forms of dementia (Alzheimer's disease and vascular dementia) seems to be related to endothelial dysfunction, i.e. pathological changes in the monolayer of cells lining the blood vessels -- in particular the endothelium of small blood vessels in the brain. There are several factors which greatly contribute toward endothelial dysfunction, such as poor nutrition, high blood glucose, lack of exercise, excess body fat, smoking, and aging. The decline in smoking by itself might explain the decline in dementia.

"I’m deeply skeptical it could be Flynn effect. ... The decline in smoking by itself might explain the decline in dementia."

Actually, the Flynn Effect is a catch-all description for anything positive related to average intelligence. It presumably has many causes.

I doubt that smoking has a significant effect on IQ, but it certainly has a profound effect on endothelial dysfunction which in turn has strong links to arteriosclerosis, type 2 diabetes, and Alzheimer's disease (by far the leading form of dementia).

A strong case can be made for smoking and exercise having an effect on Alzheimer's disease, but these are not factors cited as possible causes of the Flynn effect. Diet is a factor which may affect both Alzheimer's disease and the Flynn effect, but it's different aspects of diet in each case. Dietary antioxidant intake has been demonstrated to reverse endothelial dysfunction so it may be protective against Alzheimer's disease, but there is little or no reason to believe antioxidants affect IQ. Improved diet has been proposed as a cause of the Flynn effect, but in this case it's overall nutrition -- calories and protein -- not antioxidant intake.

There's been a huge rise in many conditions, including autism, Type 1 diabetes, Type 2 diabetes, autoimmune diseases such as MS and Celiac, and Alzheimer's (sometimes called Type 3 diabetes) in the past few decades. For some of these diseases there's already speculation that a genetic predisposition combines with an outside trigger to bring on the disease -- and speculation that the outside trigger could be viral (Coxsackie B is the leading contender, I think).

Seems like an obvious explanation for a condition rising fairly suddenly and steadily and then going into decline is that there is a microorganism component. Bacterial and viral diseases naturally have a peak in a population, as the toll they take on the mortality of those most susceptible to them starts to affect how well they can keep hold.

Just speculation, but if you find that soon other conditions begin to hit the other side of the bell curve, I hope doctors will consider giving up their Dr. Oz-based default certainty that modern disease is caused by lifestyle choices and start considering whether there is an underlying medical cause for both these conditions and many of our lifestyle choices. (I reference cautiously the Ted Talk by Peter Attia).

"Bacterial and viral diseases naturally have a peak in a population, as the toll they take on the mortality of those most susceptible to them starts to affect how well they can keep hold"

Surely you jest with regard to dementia??


Don't want to look like I'm just poking people in the eye for a reaction, but no, I'm serious.

Take leprosy -- about 95% of people have a natural genetic immunity to the disease, but the cause of the disease is bacterial.

Type 1 diabetes is what I'm familiar with, and one of the best theories out there is that a common virus almost everyone in the U.S. gets as a child triggers an autoimmune reaction in the very few that are genetically mis-wired.

I'm not saying it's so with dementia, but I find the "dementia is decreasing because of all our PSAs" explanation thinner than my theory is kooky. I realize they have found physiological precursors to symptoms in those with dementia, but what causes the precursors, isn't that still up in the air? Or am I ten years behind in my knowledge?

People with dementia live for many years. It's not like the flu. They also only get sick when old, so they could be spreading the infection to young people and those young people spreading it around for decades. It seems very unlikely that dementia is killing so many people that it is inhibiting its own spread. I suppose you would see a decrease in incidence if initially an infection spread rapidly and then the population became saturated and there was essentially no one left to infect, and then infected people started dying. But a 25% reduction?

I'm afraid I've reached the limit of my pretending to know anything about infectious disease, and I blew it by using "mortality" above. But yes, your second scenario seems plausible to me, even at that percentage -- or at least that it accounts for part of the percentage. T. Saveyn's comment below is very interesting, also. Fascinating stuff.

Or are you just noting that these folks are past reproduction? I'm not meaning some kind of accelerated evolutionary effect. I just mean the standard thing where if I get measles I'm immune the next year it comes around, assuming it doesn't kill me, so there are peaks with infectious diseases as, I think, the microbes run into populations that have no immunity, then troughs in later years.

Apparently, I'm not as brilliantly insightful as I thought I was.

Now I'll bow out before I start to look like a blog stalker.

Two more tidbits you might find of interest: (1) drugs designed to prevent or remove beta amyloid (thought to be causative but looking more like a confounder) hastened death when tested; and, (2) beta amyloid is a potent antimicrobial.

There's some debate whether autism rates actually have risen, or whether it's just a matter of borderline cases being diagnosed today.

Respectfully, I don't think there's any debate on that exactly. There's a debate on how much of the rise can be accounted for through an expansion of the definition, more accurate diagnosis (i.e. in earlier decades it might have been categorized as mental retardation or mental illness, etc.), etc. But I don't think there's any doubt that even if you generously allow for all of that the rate of increase has been dramatic.

Sorry, looked closer to see if you were right, and saw you were -- even at a 12 fold increase over 20 years many still believe it's about diagnosis, not increased prevalence. Apologize.

I forgot what I was going to say about this post.

Could this be related to the reduction of lead in the environment? Can we compare country to country, comparing countries that banned leaded fuel at different times?

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