Evidence suggests that diabetes is a risk factor for Alzheimer disease. But how does it affect those who already have AD? The results of a large, prospective French study, released in today’s Neurology, may seem counterintuitive. Writing for the REAL.FR study group, Caroline Sanz, Inserm U558, Toulouse, France, and colleagues report slower cognitive decline over a four-year period in AD patients with diabetes mellitus (DM) compared to AD patients without diabetes. The difference was apparent even after adjusting for confounding variables, such as prescription diabetes medication, and the results confirm similar findings reported in smaller studies (see Mielke et al., 2007).
Before the study, the researchers hypothesized that diabetes would accelerate cognitive decline, and they suggest several plausible explanations for the unexpected results. DM patients receive more medications, such as anti-hypertension drugs, for example, that might protect against cardiovascular risks for cognitive decline. Sanz and colleagues also posit that the underlying pathology may be different between AD patients with and without diabetes. In fact, researchers led by Suzanne Craft, University of Washington, Seattle, have shown that people with dementia and DM have more microvascular lesions and greater cognitive decline at lower plaque burdens compared to dementia patients who are DM-free (see ARF related news story). Insulin sensitivity/resistance might also be a confounding issue for those with DM. The role of insulin resistance in brain aging and dementia is the topic of an Alzforum Webinar this Thursday led by Craft. For more information and to join the discussion, see the Webinar background page.—Tom Fagan
- Mielke MM, Rosenberg PB, Tschanz J, Cook L, Corcoran C, Hayden KM, Norton M, Rabins PV, Green RC, Welsh-Bohmer KA, Breitner JC, Munger R, Lyketsos CG. Vascular factors predict rate of progression in Alzheimer disease. Neurology. 2007 Nov 6;69(19):1850-8. PubMed.
- Sanz C, Andrieu S, Sinclair A, Hanaire H, Vellas B, . Diabetes is associated with a slower rate of cognitive decline in Alzheimer disease. Neurology. 2009 Oct 27;73(17):1359-66. PubMed.