Avocados Touted as Food for the Aging Mind

Excerpts from the first in a series of articles by Rosalie Marion Bliss, Agricultural Research Service Information Staff.
For the entire article go to: Agricultural Research magazine, August 2007 issue

The oxygen radical absorbance capacity (ORAC) scores of fruits vary. In this mix of fruit, the ORAC score of blueberries is highest, followed by (in order) the scores of black plum, blackberries, raspberries, strawberries, sweet cherries, avocado, navel orange, and red grapes.

Scientists know that certain nutrients and other key chemical compounds are essential to human brain function. Serious deficiencies in some of these, such as vitamin B12 and iron, can lead to impaired cognitive function due to neurological, or nerve fiber, complications. Cognition can be defined as the ability to use simple-to-complex information to meet the challenges of daily living.

So, could careful attention to diet help protect the aging brain from problems with nerve cell signals involved in memory and cognition? A clear-cut answer could greatly affect the 77 million baby boomers who are now facing retirement. Their independence, quality of life, and even economic status will largely be defined by their ability to traffic information signals as they age.
In researching the nutrition-brain connection, new technologies are being used, such as those that take images of the brain or actually count individual brain cells. Behavioral tests that measure motor and cognitive skills—or lack thereof—are also providing insights. Yet the science of nutrition and brain function is relatively new and evolving.

The brain’s billions of neurons “talk” to one another through chemical neurotransmitters that convey signals through neural pathways. These chemical transporters—which include norepinephrine, serotonin, and dopamine—are key to signal movement.

Although people naturally lose brain cells throughout their lives, the process of neuronal death does not necessarily accelerate with aging. “There is a lot of individual difference,” says ARS neuroscientist James Joseph. “Loss of mental agility may be less due to loss of brain cells than to the cells’ failure to communicate effectively.”

“Vitamins and minerals in plant foods provide protective antioxidants,” says Joseph. “But fruits, vegetables, nuts, seeds, and grains contain thousands of other types of compounds that contribute significantly to the overall dietary intake of antioxidants.

“A partial measure of the antioxidant effect is called ‘ORAC,’ for Oxygen Radical Absorbance Capacity. ORAC scores are now showing up in charts and on some food and beverage packages. They may be helpful in choosing foods to include in your diet.”

One of the first of Joseph’s studies, published in the Journal of Neuroscience, showed a protective effect of consuming antioxidants. Study rats were fed—from adulthood to middle age—vitamin E, strawberry extracts, or spinach extracts, all with similar ORAC values. Animals receiving the high-antioxidant diets did not experience the age-related cognitive performance losses seen in control rats fed standard chow.

A later study, also published in the Journal of Neuroscience, showed a reversal of functional loss among rats on special diets. Each of three groups of rats, equivalent in age to 63-year-old humans, was fed a different high-antioxidant extract. A control group was fed standard chow. After 8 weeks—equivalent to about 10 years in humans—the rats’ performance levels were measured.
The rats fed the spinach, strawberry, or blueberry extracts effectively reversed age-related deficits in neuronal and cognitive function. In addition, the blueberry-fed group far outperformed their peers while traversing a rotating rod to test balance and coordination.

Other study results were reported in the article.