The chicken or the egg? Does glycaemic control predict cognitive function or the other way around?

The association between type 2 diabetes and cognitive dysfunction is well established. Prevention of the development of type 2 diabetes and its complications, as well as cognitive dysfunction and dementia, are leading goals in these fields. Deciphering the causality direction of the interplay between type 2 diabetes and cognitive dysfunction, and understanding the timeline of disease progression, are crucial for developing efficient prevention strategies. The prevailing perception is that type 2 diabetes leads to cognitive dysfunction and dementia. There is substantial evidence showing that accelerated cognitive decline in type 2 diabetes starts in midlife (mean age 40-60 years) and that it may even begin at the prediabetes stage. However, in this issue of Diabetologia, Altschul et al (doi : https://doi.org/10.1007/s00125-018-4645-8) show evidence for the reverse causality hypothesis, i.e. that lower cognitive function precedes poor glycaemic control. They found that cognitive function at early adolescence (age 11 years) predicts both HbA(1c) levels and cognitive function at age 70 years. Moreover, they found that lower cognitive function at age 70 is associated with an increase in HbA(1c) from age 70 to 79 years. Based on these findings, future studies should explore whether developing prevention strategies that target young adolescents with lower cognitive function will result in prevention of type 2 diabetes, breaking the vicious cycle of type 2 diabetes and cognitive dysfunction.