12 January 2009

Diabetes and Alzheimer's

Diabetes treatment and Alzheimer pathology
Dementia News (Alzheimer's Australia): 8 January 2008
To examine whether or not there might be an association between Alzheimer’s disease neuropathology and treatment for diabetes, Dr Beeri and colleagues from the Mount Sinai School of Medicine, New York; the Jewish Home and Hospital, New York; and the Bronx Veterans Affairs Medical Center undertook post-mortem studies of 124 people who had had diabetes and 124 people who had not had diabetes.

All 248 people whose brains were autopsied had been residents in an aged care facility and those in each group (that is, diabetic and non-diabetic), were matched for cognition, age at death, and sex. The group containing people with diabetes was further divided according to their recorded lifetime anti-diabetic medications: no medication; insulin; oral hypoglycemics (blood glucose-lowering medications); and combination therapy using both insulin and any oral antidiabetic medications. The mean age of those in the study was 81 years; a little over 57% were women; and each person had been clinically rated according to his or her severity of dementia.

At post-mortem the researchers examined the densities in several regions of the brain of two forms of pathology associated with Alzheimer’s disease — neuritic plaques and neurofibrillary tangles. They found differences in the rates of neuritic plaques across the five groups; the least number of neuritic plaques were seen in the diabetic group who had been given combined therapy. There were no significant differences found in rates of neurofibrillary tangles across the groups.

The researchers suggest that the combination of insulin with other diabetes medication is associated with significantly lower neuritic plaque density and that this is the result of modulation of insulin signaling in the brain.

It will be interesting to see whether these findings hold in study populations larger than this one in which there were 29 people who had received no medication for their diabetes; 49 who had received insulin only; 28 who had received medications other than insulin only; and 18 who had received both insulin and oral antidiabetic medications. The statistical significance found by the researchers may disappear in a larger study. Also, other interpretations of the findings are possible. For example, diabetes itself might affect neuronal function and plaque formation, and there may be some statistical confounding due to other variables, such as degrees of cerebrovascular disease across groups. Cerebrovascular disease is a well-known risk for Alzheimer’s disease.

The study, “Insulin in combination with other diabetes medication is associated with less Alzheimer neuropathology”, by Dr M. Beeri and colleagues is published in the journal Neurology 2008; 71: 750–757.

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