Around one-fourth of older adults in the US has diabetes mellitus (DM). It has been hypothesized that DM may contribute to cognitive decline and dementia, possibly through poor glucose control. A recent study published in the Archives of Neurology tests the hypotheses that DM increases the risk of cognitive decline, and that this increased risk is related to glucose control.
The included 3,069 older adult participants who were administered a variety of cognitive and physical assessments at multiple points over a nine-year period. All participants were physically well-functioning at baseline (the beginning of a participant’s involvement with a study), able to independently perform activities of daily living without difficulty and able to walk a quarter of a mile without resting. Individuals with and without DM were included in the sample: at baseline, 23.4% of the participants had a diagnosis of DM, and 5.2% of the participants developed DM at some point during the study.
Having a sample large enough to include a number of individuals who would develop DM over the course of the study enabled the researchers to see if these individuals then experienced an increased risk for cognitive decline. A measure of glucose control was also administered at four points during the study, enabling the researchers to further explore the possible relationship between glucose control and cognitive decline.
Participants who began the study with a diagnosis of DM had overall lower cognitive test scores at baseline than those without DM, and also showed a slightly higher rate of cognitive decline over the next nine years. This provides further support to the hypothesized relationship between DM and cognitive decline. Further, among participants with DM, individuals with relatively poorer glucose control had lower scores on cognitive tests than those with relatively better glucose control, supporting the glucose control hypothesis. Participants who developed DM during the study had average cognitive scores between those of participants without DM and of those with DM at baseline, but did not differ from those without DM to a statistically significant extent. (In other words, there was enough overlap between the range of scores within these two groups that the difference in average scores may be coincidental.) This suggests that preventing or delaying DM may be a viable way to preserve cognitive function among physically well-functioning older adults, but further research will be necessary.