ANN ARBOR—Type II diabetes has been linked to an increased risk of Alzheimer’s dementia in at least 10 well-designed, long-running studies done on diverse populations of older people. Growing evidence suggests that insulin may play an important role in this link.

Mary Haan, professor of epidemiology at the University of Michigan School of Public Health, writes about the evidence for this link in an invited review article in the March issue of the journal Nature Neurology Clinical Practice. She looked at the state of research connecting the two increasingly common diseases.

Several recent studies have looked at the involvement of metabolic, inflammatory, vascular and oxidative pathways in Alzheimer’s, and since these factors are also present in type II diabetes, they might help explain the connection between the two. Of particular importance are early findings that high insulin levels may be associated with increased risk of Alzheimer’s disease independent of type II diabetes.

These findings may be good news in that accumulating evidence supports the idea that lack of exercise and being overweight, which increase the risk of diabetes, also are related to an increased risk of Alzheimer’s. Being sedentary or obese in midlife may actually increase risk of Alzheimer’s in older ages.

Examining what is known left Haan with at least two unknowns for researchers to resolve: Are medications that treat type II diabetes also effective in preventing or treating Alzheimer’s and would preventing type II diabetes lower the risk of Alzheimer’s?

Haan is conducting research of her own into the associations between diabetes, dementia and cognitive impairment as part of the Sacramento Area Latino Study on Aging. SALSA studies the physical and mental health of older Latinos, and Haan is also leading a substudy within SALSA that is examining differences in various brain structures in normal, cognitively impaired and demented adults.

She brought that perspective to her literature review for Nature.

“There are a lot of people out there with early-stage dementia who are undiagnosed,” Haan said.” There’s a sense that older people just get forgetful and there’s nothing you can do about it.”

In SALSA, she found about 200 of 1,800 total participants had significant cognitive impairment or dementia, and most of them were not being treated at the time of the study diagnosis. That is in part because of access to health care, but also because many primary care doctors do not have the time or tools to look for early signs of dementia.

“Many people do not realize that grandma’s forgetfulness might not just be normal aging,” Haan said.

Similarly, about 50 percent of the study participants to date have type II diabetes, many undiagnosed and not controlled in any way. Only about half of those with diabetes were being treated for it.

“Treating type II diabetes can be hard, even when you’re under a doctor’s care,” Haan said. Risks of letting the disease progress unchecked include blindness, loss of limbs, stroke and kidney failure.

In this population, Haan found that type II diabetes predicted the development of dementia and Alzheimer’s?one of the first such studies showing that relationship.

Haan said one easy recommendation that can come from her work is to encourage better awareness on the part of clinicians and those developing clinical interventions. Alzheimer’s patients are not routinely evaluated for diabetes, nor do clinical trials related to diabetes typically include screening for cognitive impairment and dementia. Since early intervention with Alzheimer’s allows for better treatment, identifying cases sooner could help people retain their cognitive function longer.

Haan is writing a grant proposal to extend her work with the Latino families who participated in SALSA. She would like to collect information about the children and grandchildren of participants to see how their health status differs.

Of the 1,800 SALSA volunteers, about half are immigrants, while half were born in the U.S. Many have roots to the United States since before their home became the U.S. Haan said the stereotype is that immigrants come to America, pick up American lifestyle habits and become overweight and unhealthy. She has not seen that in her work, and wants to get a more generational view of the development of disease risks.

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