It was with interest that we read the study by Greenwood et al. (1), which investigated the impact of postprandial hyperglycemia on memory function in type 2 diabetic patients and demonstrated impaired memory function after carbohydrate ingestion. As they thoroughly discussed, the impact of glycemic control and transient hyperglycemia has been under investigation since the mid-1980s (2,3), with study results that are heterogeneous and not very conclusive. In fact, data from a study at our diabetes center (4) comprising 53 type 2 diabetic patients suggest that glycemic control has no influence on cognitive functioning, including memory (Auditory Verbal Learning Test), whereas patients with diabetic complications show lower performance.
One reason for the heterogeneity of results probably stems from the lack of consensus on which instruments to use for cognitive function assessment (5) and the usually small sample sizes. In this respect, unfortunately, Greenwood et al. did not use the standard versions of the tests for memory assessment but instead used instruments that were constructed of parallel forms and had obviously undergone profound changes, like omitting items. The precise nature of the test that was applied is not described in their previous study either (6). Although they thoroughly addressed parallels of the versions used, the possible interference effects of several verbal memory tests used in a row are not discussed.
Taken together with the small sample size, the large interindividual variability of performance within the groups, and hence the fact that the adequacy of regression analysis is disputable, in our point of view the conclusions of Greenwood et al. are daring. Surely, neuropsychological effects of transient hyperglycemic excursions are worth being studied further, but concluding that ingestion of one-half bagel and grape juice leads to acute memory impairment seems, in our opinion, too far-reaching.