Intelligence, Education, and Alzheimer's Disease

This week’s issue of ALZForum included a fascinating article about the findings of two recent research projects correlating intelligence, education, and risk for Alzheimer’s disease.

It’s known that people with higher educational attainment have a lower risk of AD as do people with higher measured intelligence. As we discussed in Beating the Dementia Monster, higher intelligence in the context of dementia is referred to as “cognitive reserve.” Do both education and intelligence have independent influence? Or is it coincidental that persons of higher intelligence will acquire more education, and the correlation with risk for AD is purely a consequence of that?
 
In one of the studies, researchers correlated a set of scores from a test taken by almost 400,000 high school students in 1960 with current Medicare usage. The actual sample was about 43,000 men and about 43,000 women. (I’m not sure how they got around the obvious privacy issues.) The tests probed general cognitive ability, language skills, perception, visualization, and mathematics, as well as complex intellectual aptitudes such as creativity and abstract reasoning. Some students had done well, and some had done not so well. At the time of the study, these people ranged in age from 66 to 73.
 
The research found that 2.9% of the men and 3.3% of the women developed AD or “related disorders.” I’m not sure what the related disorders are, but there was a strong correlation between test performance and resistance to developing AD. For you statistics buffs, for every standard deviation disadvantage a boy had with mechanical reasoning skills, there was a 17% higher chance of developing AD in old age. For girls, trouble with novel word memory yielded a 16% higher chance of developing AD in old age with each standard deviation of disadvantage.
 
The other study sought to explore whether the well-known correlation between education and dementia was due to more schooling or because the better-educated people were more intelligent to begin with and just went farther in school. One finding of their analysis was that education can, to a certain extent, improve intelligence, although this has been established previously. This points to one question that had intrigued the researchers: can additional education serve to reduce the probability of developing AD.
 
This project also worked with a large cohort of test subjects, more than 17,000. The researchers found that, for each standard deviation increase in educational attainment, the risk of AD dropped 37 percent. For every one standard deviation increase in IQ, the risk of AD went down 35 percent. But their analysis found that the influence of educational attainment went away after accounting for intelligence. Nevertheless, increased schooling as a means of AD prevention is promising to the extent that it can raise intelligence. This should be a topic of further examination.

But, there’s always a spoilsport. At the end of the article, there was an interesting comment by a research reviewer from Massachusetts General Hospital. She said that it may simply be that educated people are just more likely to eat more nutritious food, exercise more, and get treatment for cardiovascular disease, and this accounts for a lower risk of AD. Hey—maybe she read Beating the Dementia Monster!