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Research Newsletter-Fall/Winter 2008


Hiroko H. Dodge, Ph.D.
Assistant Professor
OSU Department of Public Health

The recent news published by the Alzheimer's Association is gloomy:

    "Someone develops Alzheimer's disease every 72 seconds."
    "In 2007 there are more than 5 million people in the United States living with Alzheimer's disease."
    "Without a cure or effective treatments to delay the onset or progression of the Alzheimer's, the prevalence could soar to 7.7 million people with the disease by 2030."

Alzheimer's disease (AD) is the most prevalent type of dementia. Although there is no cure, modification of lifestyle factors (e.g., diet high in antioxidant nutrients and enriched, stimulating environment) may play an important role in preventing or postponing AD onset and progression. Dementia is an age-associated disease, which means the risk of developing dementia increases as we get older. The fastest growing segment of the population in the United States and most other developed countries is that aged 85 and older (so called "the oldest old"). Unfortunately, this group has a high risk of getting dementia because old age itself is an important risk factor.

We are interested in whether diet and lifestyle explain differences in dementia prevalence. Therefore, we chose to compare Americans and Okinawans. Okinawa is the most southern island of Japan. The island is well known for its high prevalence of centenarians, and past studies have shown that Okinawan elderly not only live longer, but also survive with better physical and cognitive health. Table 1 shows life expectancy for Americans and Okinawans at birth, age 65, and age 85.

Table 1

At age 85, Okinawan women live 9.0 more years on average, while U.S. elderly women live 6.7 more years. Two years difference in life expectancy at this old age is a very big difference. Table 2 shows the prevalence of dementia in the elderly in the U.S. and Okinawa. The Okinawan elderly seem to have a lower prevalence of dementia. One important factor contributing to their health suggested by the Okinawa Centenarian Study is their low total caloric and saturated fat intake, along with a diet rich in fruits and vegetables.

Table 2

A pilot grant from the Linus Pauling Institute allowed us to examine whether Okinawans have higher amounts of antioxidant nutrients in their blood, possibly prolonging their healthy lifespan and helping maintain cognitive function.

We recruited participants in Oregon and Okinawa who were age 85 and older. They were functionally independent and had no major diseases that require visiting a doctor once per month or more. They also had normal cognitive functions, an absence of significant depressive symptoms, and sufficient vision and hearing to complete neuropsychological testing.

For the Oregon sample, we used the stored serum samples of 135 subjects who participated in a Ginkgo biloba clinical trial between 2000 and 2001 (published in Neurology in 2008). We analyzed the blood sample collected at the baseline before the subjects received Ginkgo biloba and vitamin E supplements. For the Okinawan sample, we enrolled 62 subjects who met the inclusion criteria listed above.

Among the relatively healthy elderly participants age 85 and older, the Oregon group contained over 56% obese (BMI>25) and 31% with high triglycerides. The prevalence of these factors was significantly higher than among the Okinawan elderly, of whom about 30% were obese and 13% had high triglycerides. Both groups had a high proportion with hypertension (85% and 87% for Okinawan and Oregon groups, respectively). Metabolic syndrome is characterized by abdominal obesity, elevated triglycerides, high blood pressure, and other factors. People with this condition have an increased risk for heart disease and diabetes, and some studies have shown an association between metabolic syndrome and AD risk, especially among those with atherosclerosis. Therefore, our results among the Oregonians raise some concerns regarding their risk of getting AD in the future. On the other hand, Okinawan elderly had a higher proportion of those with high sodium. It is well known that the Japanese diet is low in fat but high in salt, which contributes to hypertension and resultant cerebrovascular diseases. For example, in 2005, 6.6% of total deaths in the U.S. were from cerebrovascular diseases, while the rate in Japan was 12.3%, almost twice as high as the U.S. rate. On the other hand, 28.9% of total deaths in the U.S. were due to heart disease, but in Japan it was only 16.0%.

At the beginning of the study, the concentration of alphatocopherol (vitamin E) in the blood from Okinawans and Oregonians was nearly identical, but blood samples from Oregonians had more than twice the concentration of gamma-tocopherol, which is the most common form of vitamin E in the American diet.

Folate levels in blood are three times higher in the U.S. subjects than in Okinawans. Since 1998, it has been mandatory in the U.S. to fortify cereals and flour with folate. Possibly because of this high folate intake, Oregonians' homocysteine levels were slightly lower than those in Okinawa, but the difference did not reach statistical significance.

We are going to follow the same participants in Okinawa for two more years. We plan to examine whether the micronutrient values collected at baseline will predict cognitive well-being and/or survival longitudinally. We will keep you updated on what we find in the future.

Last updated January 2009