Sex matters: Diabetes and the brain

We have previously discussed the adverse effects of diabetes on the brain. It is known that the hippocampus is particularly vulnerable and preferentially damaged in Type 2 diabetes and studies have shown that its volume decreases by about 12% in diabetic populations. Other brain structures are also affected. Diabetes can also have adverse effects on other organ systems and studies show that males and females are differentially affected. For example, diabetes leads to a greater relative risk of cardiovascular disease in women than men.

Sex differences in the brain
With the development of human brain-imaging techniques, such as MRI and PET, studies of sex differences in brain morphology became more common and numerous sex differences in the human brain have been documented. Males have larger brains than females and this difference can not be entirely explained by body size. However, the significance of this remains unknown. It has even been suggested that a larger brain does not have any functional significance, just like having a bigger nose does not have a any particular benefit! Different neural circuitry, size, or neurochemistry of certain areas in the brain of males and females are probably more interesting than differences in whole brain volume and should be more easily related to differences in function or cognitive ability. The hippocampus – shown in red in the illustration – which has a critical role in memory and learning is, for example, generally larger in females. It seems obvious that such sex specific differences need to be taken into account in various medical and neuroscientific studies.
In a recent study, Hempel, Onopa and Convit at the New York University School of Medicine compared hippocampal volumes in patients with Type 2 diabetes and healthy controls, matched in age, education and other relevant variables. Their goal was to determine how reduction in hippocampal volume might be affected by gender. This was the first study to address this issue. Their results showed that the hippocampus in female diabetics was more affected than in their male counterparts, even though the women´s glucose levels were better controlled. How this is related to earlier findings that healthy women, on average, have larger hippocampi than males, is not discussed in the study. Only a longitudinal cohort study could address this question and further studies are needed to replicate the findings of Hempel, Onopa and Convit.

Don´t forget the women!
In medical research health issues particular to females were ignored for too long. Similarly sex differences have been neglected in neuroscientific research. Following a workshop entitled Sex Differences in Brain, Behavior, Mental Health and Mental Disorders in 2011, the National Institute of Health in the US encouraged neuroscientists to include sex as a variable in their research, that is, to focus more on sex differences than previously has been done. This is a great step forward and hopefully researchers will rise to the challenge as Hempel and colleagues have done.

Cahill, L. (2006). Why sex matters for neuroscience. Nature Reviews Neuroscience, 7, 477-484.

Eliot, L. (2011). The trouble with sex differences. Neuron, 72, 895-898.

Hempel, R., Onopa, R. & Convit, A. (2012). Type 2 diabetes affects hippocampus volume differentially in men and women. Diabetes and Metabolic Research Revue, 28 (1), 76-83.

McCarthy, M., Arnold, A. P., Ball, G. F., Blaustein, J. D., De Vries, G. J. (2012). Sex differences in the brain: The not so inconvenient truth. The Journal of Neuroscience, 32 (7), 2241-2247.

Illustration credit: By Images are generated by Life Science Databases(LSDB). [CC-BY-SA-2.1-jp (], via Wikimedia Commons

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