A Surprising Link Between Diabetes and Alzheimer's

By KAREN BARROW

06 feb 2009--Dr. Margaret Gatz, a professor of psychology, gerontology and preventative medicine at the University of Southern California, conducts research on interventions that may reduce the risk of Alzheimer’s disease. In a recent study, published in the January 2009 issue of the journal Diabetes, Dr. Gatz and her team tracked rates of dementia and diabetes in Swedish twins and discovered that developing type 2 diabetes before the age of 65 was associated with a 125 percent increased risk of subsequently developing Alzheimer’s disease.

1. How did you become interested in the relationship between diabetes and dementia?

Our research began with the question why some people develop dementia, especially Alzheimer’s disease, in old age, whereas others do not. Alzheimer’s disease is the most common type of dementia, followed by vascular dementia, which is generally caused by the same things that are risk factors for stroke.

Recently, a number of researchers have begun to show that vascular risk factors are important not only for increasing risk of vascular dementia but also for increasing risk of Alzheimer’s disease. This observation is particularly interesting because vascular risk factors are potentially modifiable. In other words, people might be able to reduce their risk of Alzheimer’s disease by attending to the kinds of health behaviors that reduce vascular risk, such as controlling blood pressure, cholesterol and diabetes. What led our research group to be interested in diabetes was the search for potential ways to lower risk of Alzheimer’s disease.

We were fortunate to be able to launch the Study of Dementia in Swedish Twins, building on the Swedish Twin Registry, to identify a population of twins where one or both members of the pair have developed dementia. Because the participants are twins, they are genetically similar, and that permits us to ask specifically what is different in the lives of those twins when one has dementia and the other does not.

2. What is most surprising about your findings?

Two findings are particularly intriguing. One is that diabetes was a risk factor for both vascular dementia and for Alzheimer’s disease, although the association was more robust for vascular dementia than for Alzheimer’s disease. The second is that diabetes that first occurred before age 65 was a far more important risk factor for dementia than diabetes that did not occur until after age 65.

While it is possible that long-term diabetes or its treatment may cause some sort of damage to the brain, it is also possible that the diabetes is not so much the cause of the dementia, but rather that diabetes and dementia each arise from the same environmental exposures and influences. For example, the same adverse early childhood conditions that lead to higher rates of diabetes (such as a low birth weight) may also affect brain development. Thus, we conclude in our paper that a complex interplay of genetic factors and environmental exposures throughout the entire life course likely affects risk of dementia in old age.

3. Do you believe that appropriate treatment for diabetes and good diabetes control could have an impact on lowering the likelihood of developing dementia? Or are prolonged treatments a potential part of the problem?

In our study, we could not separate diabetes from its treatment or identify those with well controlled versus poorly controlled diabetes. However, the association between mid-life diabetes and dementia was still significant after adjustment for diabetes duration. In other words, our results suggest that age of diabetes onset itself might be an important factor in later dementia risk, not so much how prolonged the diabetes treatment had been.

4. With rising rates of diabetes and longer life spans, do you suspect that there also will be a rise in dementia rates among the elderly?

Because dementia is an age-related condition, with longer life spans the number of people with dementia can be expected to rise, unless we make real progress in identifying modifiable risk factors and treatments for dementia. While there is much still to learn about the mechanisms behind the link between diabetes and dementia, it does seem likely that some of the same preventive steps that could reduce rates of diabetes will figure in discussions of how to reduce risk of dementia.

5. What is the next step in your research?

Currently, we are looking at other vascular risk factors for dementia: cardiovascular disease, obesity and blood lipids. In addition to focusing on dementia per se, we are also looking at the change in cognition with normal aging and the relationship of those changes to diabetes, obesity and blood lipids. We are particularly interested in inflammatory-related health conditions, because these might offer insight into the causes of Alzheimer’s disease and help to refine recommendations to people about how to reduce their risk for developing Alzheimer’s disease.