Researchers from France and the UK who set out to investigate whether people with Alzheimer's disease and diabetes have more rapid memory
loss were surprised to find not only that they did not, but that their memory loss was actually slower than that of Alzheimer's patients without diabetes.
Speculating on the reasons, they suggested it could be the effect of diabetes drugs, or that Alzheimer's patients with diabetes have different kinds of
lesions in the brain.
The study was the work of first author Dr Caroline Sanz, of INSERM, the French National Institute for Health and Medical Research in Toulouse, and colleagues, and is published in the 27 October print issue of Neurology, the medical journal of the American Academy of Neurology.
The researchers already knew from previous studies that diabetes increases the risk of Alzheimer's disease and the risk of memory loss in people who don't have Alzheimer's, but it was unclear whether people with both Alzheimer's and diabetes experienced more rapid memory loss.
Sanz told the press that their findings surprised them:
"Our initial hypothesis was that diabetes would increase the rate of cognitive decline in people with Alzheimer's disease."
For the study, which was sponsored by the French Ministry of Health and the Toulouse University Hospital, the researchers followed 608 community-dwelling patients with mild to moderate Alzheimer's disease for 4 years, during which time they tested their thinking and memory skills twice a year with the commonly used MMSE (mini mental state examination) test of cognitive function.
63 of the 608 participants (10.4 per cent), also had diabetes.
The authors found that after applying a "mixed model" to take into account "sex, age, educational level, dementia severity, cholinesterase inhibitor use, and vascular factors (hypertension, atrial fibrillation, coronary heart disease, and hypercholesterolemia)", the results showed that:
- At the start of the study period, both groups (Alzheimer's patients with and without diabetes) had the same average MMSE scores of 20.
- Over each six-month testing period, the overall group score went down by an average of 1.24 points.
- However, those without diabetes declined by 0.38 points more per six-month period than those with diabetes.
"In a cohort of community-dwelling patients with Alzheimer disease (AD), the presence of diabetes mellitus (DM) was associated with a lower rate of cognitive decline."
"Future studies will need to address the potential impact of DM in the cerebral aging process and to assess the neuropathologic variations in patients with AD with DM," they added.
Speculating on the reasons why they found that the rate of cognitive decline was slower for the Alzheimer's patients in their study, Sanz suggested that:
"One possible explanation is that diabetes in the elderly differs from that in younger people and in addition, elderly people with diabetes may be more likely to receive cardiovascular medications such as drugs for high blood pressure than people who don't have diabetes."
"These drugs have been reported to decrease the risk of developing Alzheimer's disease and also the rate of cognitive decline in people with Alzheimer's disease," she added, explaining that another reason for these findings could be due to:
"Differences in brain lesions in those people with diabetes compared to those without diabetes."
"Diabetes is associated with a slower rate of cognitive decline in Alzheimer disease."
C. Sanz, S. Andrieu, A. Sinclair, H. Hanaire, B. Vellas For the REAL.FR Study Group.
Neurology, Oct 2009; 73: 1359 - 1366.
Source: American Academy of Neurology.
Written by: Catharine Paddock, PhD