The first study to follow IQ in type 1 diabetes patients from diagnosis in childhood into young adulthood has shown that the condition can affect some aspects of IQ.
The findings published in Diabetes Care,show evidence of a selective impact of specific disease risk factors on IQ.
A diagnosis with type 1 diabetes at an earlier age was associated with a decline in visuospatial [performance] aspects of IQ, while hypoglycemic seizures, but not hyperglycemia, appear to affect verbal IQ [word knowledge and abstract verbal conceptual reasoning],” lead investigator Dr Ashleigh Lin (Telethon Kids Institute, University of Western Australia, Perth) told Medscape Medical News.
Although these associations are not novel, access to IQ scores from diagnosis through 12 years of follow-up into young adulthood provides “particularly compelling evidence that the timing of diabetes onset and exposure to serious hypoglycemia are significant factors in the cognitive sequelae of type 1 diabetes,” the researchers say.
“We know that, years after diagnosis, young people with type 1 diabetes show lower IQ, particularly if they are diagnosed early — age 5 or younger — or have a history of hypoglycemic seizures,” explained Dr Lin.
Method of Study
Dr Lin and colleagues prospectively followed 95 patients admitted at diagnosis of type 1 diabetes to the Royal Children’s Hospital, Melbourne, Australia, between 1990 and 1992 and compared them with 67 healthy controls.
Dr Lin remarked that their study was unique in design because it was the first to follow children periodically from time of diagnosis, as well as following healthy participants recruited at the same time as those with diabetes.
“Being able to follow up both groups of children into young adulthood 12 years later is an achievement, especially since the majority of the cohort had transitioned into adult diabetes services and were no longer managed at the Royal Children’s Hospital,” she noted.
Measures of IQ included the Wechsler Preschool and Primary Scale of Intelligence—Revised, Wechsler Intelligence Scale for Children—Revised, and Wechsler Abbreviated Scale of Intelligence, providing scores for full-scale IQ, verbal IQ, and performance IQ.
Data on metabolic control history were also prospectively collected.
The Effects of Hypoglycaemia on IQ
The negative impact of severe hypoglycemia on language-skills development has been reported by other researchers, but the reasons for this association remain unknown, Dr Lin pointed out.
“We know that language skills are sensitive to educational opportunity. Children who are prone to hypoglycemia may be less efficient learners in the classroom because low blood glucose levels impair concentration in the school setting, having a cumulative negative impact on language development,” she speculated.
“We also know that frontal-temporal regions of the brain require high levels of glucose, so glucose deprivation may impair skills such as semantic memory, which underpin optimal language development.
No Link to Poor HbA1c Levels & IQ
However, in contrast to other groups that have shown that poor metabolic control is associated with lowered cognitive ability, Dr Lin and colleagues were unable to find a significant association between HbA1c measurements and changes in IQ.
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