“OBJECTIVE Hippocampal neurons in adult animals and humans are vulnerable to severe hypoglycemia and hyperglycemia. Effects are hypothesized to be exacerbated during development, but existing studies on developing human brains are limited. We examined whether hypoglycemia or hyperglycemia experienced during brain development in humans affects hippocampal volumes.
RESEARCH DESIGN AND METHODS We analyzed T1-weighted magnetic resonance images in 95 youth with type 1 diabetes and 49 sibling control subjects aged 7–17 years. Youth with diabetes were categorized as having 0 (n = 37), 1–2 (n = 41), or 3 or more (3+; n = 17) prior severe hypoglycemic episodes. Hyperglycemia exposure was estimated from median lifetime A1C, weighted for duration of diabetes. Stereologic measurements of hippocampal volumes were performed in atlas-registered space to correct for whole brain volume.
RESULTS Greater exposure to severe hypoglycemia was associated with larger hippocampal volumes (F [3,138] = 3.6, P = 0.016; 3+ larger than all other groups, P < 0.05). Hyperglycemia exposure was not associated with hippocampal volumes (R2 change = 0.003, F [1,89] = 0.31, P = 0.58, semipartial r = 0.06; one outlier removed for high median A1C), and the 3+ severe hypoglycemia group still had larger hippocampal volumes after controlling for age of onset and hyperglycemia exposure (main effect of hypoglycemia category, F [2,88] = 6.4, P = 0.002; 3+ larger than all other groups, P < 0.01).
CONCLUSIONS Enlargement of the hippocampus may reflect a pathological reaction to hypoglycemia during brain development, such as gliosis, reactive neurogenesis, or disruption of normal developmental pruning."
"Greater exposure to severe hypoglycemia during childhood was associated with enlargement of hippocampal gray matter volume in youth with type 1 diabetes. This effect was not explained by age, sex, degree of hyperglycemia exposure, age of onset, or duration of disease and was equivalent for both hemispheres. Although the direction of the effect was unexpected, the fact that the subset of youth with three or more severe hypoglycemic episodes in their past was different from all other groups, including sibling control subjects, supports the sensitivity of the hippocampus to effects of repeated hypoglycemic episodes during brain development. These data do not support the idea that chronic hyperglycemia in childhood affects gray matter volume in the hippocampus."
From a new study, Hippocampal Volumes in Youth With Type 1 Diabetes, by Hershey, Perantie, Wu, Weaver, Black and White (no, I’m not making those last two names up, go take a look at the link).
If I’d participated in the study, I’d have been in the 3 or more group (the ‘more group’ part of the ‘3 or more group’, to be more specific).