Cognitive ability, genes and diabetes (contribution to an invited symposium: Intelligence)

There is a well-established association between diabetes and slightly lower cognitive ability, which is commonly interpreted as the former causing the latter. However, the many findings of cognitive epidemiology showing that low childhood or young-age cognitive ability predicts less healthy lifestyle and ill-health decades later suggest the need to consider other causal interpretations. Here, I present the findings of two related studies. In one study, we compared the scores of the same general cognitive ability test of people with and without diabetes at age about 70 years at two time-points: concurrently to diabetes assessment and about 59 years earlier (at age 11), when any diabetes diagnoses would have been unlikely. Scores of those with diabetes were lower by a similar amount at both time-points, suggesting that diabetes was unlikely to impair general cognitive ability in this group of people. Instead, individual differences in cognitive ability, which are relatively stable over decades, might have contributed to variation in diabetes, or diabetes and cognitive ability variation might have common genetic or early-life causes. In another study, we tested for the potential role of cognitive ability as a moderator of diabetes genetic risk manifestation. In particular, we hypothesized that low cognitive ability might facilitate genetic risk manifestation of diabetes, whereas high cognitive ability might offer (environmental) protection against it. Diabetes genetic risk was quantified as the aggregated effect of up to nearly 200,000 thousand single-nucleotide polymorphisms. The hypothesis was confirmed, suggesting that one of the mechanisms by which cognitive ability might relate to diabetes is by modifying its genetic risk manifestation.