• Diabetes may increase risk of dementia, study says

    October 2011

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    Research in recent years has implicated Type 2 diabetes in the development of Alzheimer’s disease and other forms of dementia. Now a new study, published Sept. 20, 2011, in the journal Neurology, makes a stronger case for this relationship.

    In the study, Japanese researchers set out to investigate the association between glucose tolerance and the development of dementia. They reasoned that previous studies had employed inconsistent definitions of dementia and diabetes. Thus, they used an oral glucose tolerance test (OGTT) as the gold standard for diagnosing diabetes. This involves giving a person a sugar-loaded drink after they have fasted for 12 hours, then measuring how much glucose remains in their blood after two hours. The diagnosis for dementia was made by scanning the brains of living patients and brain autopsies of deceased patients.

    More than 1,000 men and women over the age of 60 from the same Japanese city were recruited for the study and followed for 15 years. Researchers adjusted for age, sex and other potential risk factors for dementia. They found that participants with confirmed diabetes had almost twice the likelihood of developing Alzheimer’s disease and other forms of dementia as those who were diabetes free.

    Seriousness of these diseases

    Type 2 diabetes is one of the most common metabolic diseases in the world and its prevalence has risen in recent years. Kentucky ranks ninth in the nation for diabetes; 9.9 percent of the state’s population has this disease, as opposed to 8.1 percent of the U.S. population. While there is no cure, diabetes can be controlled. More important, at least 80 percent of the cases can be prevented with lifestyle changes.

    At the same time, incidence of Alzheimer’s disease, one of the most feared maladies in the world, is expected to rise with the aging population. According to the Alzheimer’s Association, 5.4 million Americans have been diagnosed with this condition. Some projections put that number at 14 million by the year 2040, adding to the urgency to find a cure for this disease.

    “Participants with confirmed diabetes had almost twice the likelihood of developing Alzheimer’s disease and other forms of dementia as those who were diabetes free.”

    Age and family history are the greatest risk factors for Alzheimer’s disease. Other risk factors include head injuries, being female and lower education levels. The first sign of Alzheimer’s may be cognitive impairment, for example, frequent repetition of stories or questions, difficulty in driving without getting lost, problems in dealing with finances or talking over the phone, and difficulty in preparing meals.

    How dementia and diabetes are related

    In the Japanese study, participants who were more resistant to insulin were also more likely to develop amyloid plaques. Additionally, high blood sugar, which is caused by insulin resistance, produces oxygen-containing molecules that can damage cells. And high blood sugar, coupled with high cholesterol, can lead to vascular dementia, brought on by artery blockages that can also damage brain cells.

    “Our findings emphasize the need to consider diabetes as a potential risk factor for all-cause dementia, Alzheimer’s disease and probably vascular dementia,” the researchers state.

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Page last updated: 8/7/2015 2:06:38 PM
  • What the news means for you

    Making lifestyle changes can offer some protection

    Gregory A. Jicha, MD, PhD

    Wright, Heather, MDThe Japanese study is very timely because of another recent study, showing that insulin delivered directly to the brain through a special inhaler seems to improve memory and thinking. Similar studies are being planned in the United States. The data looks very promising. Alzheimer’s is such a devastating disease, and we have to attack it in every way we can.

    “If a person has diabetes that doesn’t mean he or she will get Alzheimer’s disease.” 

    The data associating diabetes with dementia is not new. It’s been looked at for 20 years, with some studies suggesting there is a relationship, others saying there isn’t. Defining diabetes has caused confusion because, in some cases, research subjects were not tested but reported themselves as having or not having diabetes. The Japanese researchers in this study used rigor in establishing the relationship by diagnosing diabetes with an oral glucose tolerance test, which is considered the gold standard. Glucose is the final, major energy source for the body. How we process sugar is important, and that’s where we look for links to the relationship between Alzheimer’s and diabetes.

    Putting the results in perspective

    It’s important to remember that if a person has diabetes that doesn’t mean he or she will get Alzheimer’s disease. In fact, most of the subjects in this study who had diabetes did not develop Alzheimer’s. Perhaps the association between these two diseases will create an impetus for lifestyle modifications and encourage people to move toward healthier habits. We know that Type 2 diabetes increases the risk of memory loss. If we treat diabetes, the risk can be reduced, as can the risks for heart disease and blindness.

    Diagnosing dementia

    The diagnosis of dementia is even more complex. Unfortunately, the default response to almost all forms of dementia or memory loss is, “You have Alzheimer’s disease.”  But there are many forms of dementia. One of the most prevalent is vascular dementia. We’ve known for years that diabetes can lead to atherosclerosis and cardiovascular disease, which includes strokes.

    And there is an overlap in the types of dementia. For instance, 70 percent of the people with Alzheimer’s will have some degree of vascular pathology that contributes to memory problems. Likewise, a person who has had a stroke may have some degree of Alzheimer’s pathology. So how much of a risk is due to vascular changes in the brain versus the role of diabetes in the development of Alzheimer’s? In the long run, it probably doesn’t matter.

    Importance of lifestyle changes

    Exercise and a healthy diet reduce the risk for having Alzheimer’s even more than not having diabetes. You should exercise 20 minutes a day. And I don’t mean just walking around an office building all day, but getting out there and getting your heart rate up. There is also a wealth of data that the Mediterranean diet may delay Alzheimer’s by years and years. This is a diet rich in vegetables, low in red meat, and includes more fish and olive oil.

    Research and the aging brain

    At the UK Sanders-Brown Center on Aging, we have been following 800 normal research participants over the age of 70 to see how the normal healthy brain ages. Participants have consented to genetic testing and to donating their brains after death. Studying their physical, neurological, memory and thinking changes has helped us better understand normal age-related changes in memory and thinking. These changes differ from the severe decline seen in Alzheimer’s disease.

    Gradual changes in the brain studied

    One area of research that has exploded in recent years is the idea that Alzheimer’s doesn’t occur all of a sudden, like a stroke. People with the earliest form of Alzheimer’s have some memory problems but can still perform their normal daily functions. They may have some mild cognitive impairment but not yet Alzheimer’s.

    In these people, PET scans can show changes in the brain. We can look at MRIs of the brain for proteins altered in Alzheimer’s or examine spinal fluid. Approximately 20 to 30 percent of the population over 65 in this country has these biological changes that occur in Alzheimer’s. So we have to find ways to prevent or treat the disease.

    One thing we can do is use the tools we have – PET scans, MRIs, spinal taps – to diagnose these changes before a person has significant memory problems, then develop medications to stop Alzheimer’s. The reason we’ve been reluctant to screen the normal population is that, if the results are positive, we really don’t have adequate therapies to treat the disease. But rest assured, researchers here at UK and around the globe are testing dozens of potential experimental treatments designed to slow, stop or even cure Alzheimer’s disease.

    Dr. Jicha is a neurologist with the Kentucky Neuroscience Institute, seeing patients in the Memory Disorders Clinic. He is also director of the Telemedicine Cognitive/Memory Clinic serving all of Kentucky, clinical core director of the Alzheimer's Center at UK's Sanders-Brown Center for Aging, and an assistant professor of neurology in the UK College of Medicine. He is listed among the Best Doctors® in America.

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