Childhood Intelligence Linked to Alzheimer’s Risk

Is Alzheimer’s disease already brewing in a person’s brain when he or she is a young adult? Scarier still, is the devastating disease already doing its dirty work in the brain of a youngster? These notions may sound “way out,” but there is accumulating evidence that it might be happening.

Five years ago, for instance, researchers reported that nuns who had written autobiographies as young women showing sparse thought content were found many years later, that is, in their 70s, 80s, and 90s, to be more susceptible to Alzheimer’s than were nuns who had written letters as young women showing a rich thought content.

And now Scottish researchers report that youngsters who had performed poorly on intelligence tests were found many years later to be more susceptible to Alzheimer’s disease than were youngsters who had done better on intelligence tests. Their findings appear in the November 28, 2000, issue of Neurology.

L.J. Whalley, M.D., a psychiatrist with the Clinical Resarch Centre in Aberdeen, Scotland, and his colleagues used records from an intelligence test that was given to some 87,000 Scottish children in 1932 in order to identify their intelligence test scores. All the children were 11 years old at that time, and the test was given at that point because 11 years marks the transition from primary to secondary school in Scotland.

The test, developed by the Scottish Council for Research and Education, was made up of 75 items that comprised a variety of item types—following directions, same-opposite, word classification, analogies, practical items, reasoning, proverbs, arithmetic, spatial items, mixed sentences, and so forth. The maximum possible score was 76. The mean score achieved by the children was 34.5.

The researchers then used a national survey of early-onset dementia, local mental health services, and a survey of Aberdeen residents who had taken the 1932 intelligence test to identify which of the individuals who had taken that test had come down with early-onset Alzheimer’s disease a number of years later, that is, when they were in their 40s and 50s.

The researchers identified 59 subjects and then selected two controls for each of these 59 subjects who had also taken the 1932 intelligence test, but who had not succumbed to early-onset Alzheimer’s. The controls were of the same sex as the subject, had had fathers with occupations similar to those of the subject’s father, and had grown up in the same district as the subject.

The investigators then compared the 1932 intelligence scores of the 59 subjects with early-onset Alzheimer’s with those of the 118 controls to see whether there was any statistically significant difference between them. There was not, the investigators found. Thus, there appears to be no link between childhood intelligence level and early-onset Alzheimer’s, the researchers concluded.

However, they also attempted to find out whether there might be any relationship between childhood intelligence and vulnerability to Alzheimer’s disease later in life. Here, they identified 50 subjects who had taken the intelligence test in 1932 and who were known to have come down with late-onset Alzheimer’s (that is, Alzheimer’s at 64 years of age or later) some time between 1986 and 1997. All of these subjects had been children in Aberdeen. The researchers then compared the intelligence test scores of these subjects at age 11 with those of about 2,700 other 11 year olds who had also lived in Aberdeen in 1932 and who had also taken the intelligence test.

The mean test score for the 50 late-onset Alzheimer’s subjects was found to be significantly below that of the others, suggesting a link between lower childhood intelligence and late-onset Alzheimer’s.

However, the researchers went even further to see whether they could confirm this link. This time they identified 772 persons who had been children in Aberdeen, who had taken the 1932 intelligence test, but who were known not to have gotten late-onset Alzheimer’s. The researchers wanted to know how their 1932 intelligence test scores matched up against those of the 50 subjects who were known to have succumbed to late-onset Alzheimer’s. Would the scores for the 50 subjects be lower than those of persons who were without Alzheimer’s? The answer was yes.

For instance, 45 of the 50 Alzheimer’s subjects were still alive in 1993. So were 639 of the 772 non-Alzheimer’s controls. The test scores of the 45 subjects were significantly below those of the 639 controls. In 1995, 41 of the Alzheimer’s subjects were still alive. So were 586 of the non-Alzheimer’s controls. Once again the test scores of the Alzheimer’s subjects were significantly below those of controls.

A similar pattern repeated itself in 1997. Thirty-four of the Alzheimer’s subjects were still alive. So were 552 of the controls. Once again the test scores of the Alzheimer’s subjects were significantly below those of controls.

So all in all, the investigators concluded, the data seem to suggest that “late-onset dementia is associated with lower mental ability scores in childhood.”

Assuming, of course, that there is truly a link between lower intelligence in childhood and late-onset Alzheimer’s, the question is: What does it mean?

One possibility, Whalley and his colleagues believe, is that persons who are of lower intelligence in childhood might engage in certain behaviors later in life that would put them in greater danger of getting Alzheimer’s disease. For instance, persons of lower childhood mental ability might be more likely to eat a poor diet, smoke, shun exercise, and so on.

Or lower intelligence in childhood might actually be a sign that Alzheimer’s disease is already prepping the brain for the disease. As Richard Mayeux, M.D., a neurologist with Columbia University in New York City, wrote in an accompanying editorial, “If Alzheimer’s disease is developmental, then the lower intelligence scores may reflect the earliest signs of the disease. This could then affect school performance, discouraging further schooling. These results may suggest that having less education is the result of Alzheimer’s disease, not the cause of it [which some research suggests].”

And if Alzheimer’s disease is truly a developmental disease, not just a disease of late age, there could be a practical consideration here: When should preventive interventions begin? ▪