Nutrition&Brain Function
Total Page：16
File Type：pdf, Size：1020Kb
FIRST IN A SERIES NUTRITION&BRAIN FUNCTION STEPHEN AUSMUS (D833-1) Food for the Aging Mind cientists know that certain nutrients protect the aging brain from problems with or actually count individual brain cells. and other key chemical compounds nerve cell signals involved in memory Behavioral tests that measure motor and S are essential to human brain and cognition? A clear-cut answer could cognitive skills—or lack thereof—are function. Serious deficiencies in greatly affect the 77 million baby boom- also providing insights. Yet the science of some of these, such as vitamin B12 and ers who are now facing retirement. Their nutrition and brain function is relatively iron, can lead to impaired cognitive independence, quality of life, and even new and evolving. function due to neurological, or nerve economic status will largely be defined by Agricultural Research Service scientists fiber, complications. their ability to traffic information signals at several locations nationwide are con- Cognition can be defined as the ability as they age. tributing to a growing body of research to use simple-to-complex information to In researching the nutrition-brain con- that explores the effect of diet and nutri- meet the challenges of daily living. nection, new technologies are being used, tion on the brain and its function across So, could careful attention to diet help such as those that take images of the brain the lifespan. 8 Agricultural Research/August 2007 424069.indd 8 7/5/07 9:24:06 AM Boosting Neuronal Function The brain’s billions of neurons “talk” ORAC Units* to one another through chemical neu- (micromole TE/ gram) rotransmitters that convey signals through neural pathways. These chemical trans- 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 porters—which include norepinephrine, serotonin, and dopamine—are key to Blueberries (1/2 cup or 72.5 grams) signal movement. Although people naturally lose brain cells throughout their lives, the process Black plum (1 plum or 66 grams) of neuronal death does not necessarily accelerate with aging. “There is a lot of individual difference,” says ARS neuro- Blackberries (1/2 cup or 72.5 grams) scientist James Joseph. “Loss of mental agility may be less due to loss of brain Raspberries (1/2 cup or 61.5 grams) cells than to the cells’ failure to commu- nicate effectively.” Joseph heads the Neuroscience Laboratory at the Jean Mayer USDA Strawberries (1/2 cup or 83 grams) Human Nutrition Research Center on Aging (HNRCA) at Tufts University in Boston. There, researchers are looking Sweet cherries (1/2 cup or 72.5 grams) at the beneficial effects of certain dietary plant compounds to learn how they affect brain function. Avocado (1/2 fruit or 86.5 grams) “Vitamins and minerals in plant foods provide protective antioxidants,” says Joseph. “But fruits, vegetables, nuts, Navel orange (1/2 fruit or 70 grams) seeds, and grains contain thousands of other types of compounds that contribute significantly to the overall dietary intake Red grapes (1/2 cup or 80 grams) of antioxidants. “A partial measure of the antioxidant ef- Source: USDA-ARS, Arkansas Children’s Research Center, Little Rock, AR, 2004 data. fect is called ‘ORAC,’ for Oxygen Radical Absorbance Capacity. ORAC scores are *ORAC units include both fat- and water-soluble values. Micromole TE/gram means the now showing up in charts and on some number of micromoles of Trolox, a vitamin E equivalent, per 1 gram weight of fresh fruit. food and beverage packages. They may be helpful in choosing foods to include in your diet.” Perhaps there is no better place in which Many in the series are groundbreaking age: It does, but at a much slower rate. to gauge the power of antioxidants than in that they challenge the long-accepted One of the first of Joseph’s studies, between the minute connections of the belief that the central nervous system, published in the Journal of Neuroscience, nerve cells. which includes the brain, is not capable of showed a protective effect of consuming regenerating itself. Other published studies antioxidants. Study rats were fed—from Bucking Long-Held Dogma in the series echo similar findings based on adulthood to middle age—vitamin E, Eight years ago, Joseph and colleagues primate and human brain research at the strawberry extracts, or spinach extracts, began publishing a series of studies, done Salk Institute for Biological Studies, San all with similar ORAC values. Animals in rodents, that shed light on the relation- Diego, California. Scientists there, using receiving the high-antioxidant diets did ship between various diets and the mecha- new technologies, disputed the notion that not experience the age-related cognitive nisms behind cognitive losses in specific the brain does not make new neurons—a performance losses seen in control rats neighborhoods of the aging brain. process called “neurogenesis”—into old fed standard chow. Agricultural Research/August 2007 9 424069.indd 9 7/3/07 10:06:39 PM STEPHEN AUSMUS (D835-1) A later study, also published in the Jour- levels of dopamine than were found in nal of Neuroscience, showed a reversal of the other groups. Dopamine has many functional loss among rats on special diets. functions within the brain. In particular, Each of three groups of rats, equivalent it can affect the way the brain controls in age to 63-year-old humans, was fed a movements. different high-antioxidant extract. A con- “We suspected that the combined anti- trol group was fed standard chow. After oxidant potency of compounds in blueber- 8 weeks—equivalent to about 10 years ry extract may have reduced inflammatory in humans—the rats’ performance levels compounds in the brains of these older were measured. animals,” says Joseph. “Inflammation The rats fed the spinach, strawberry, ordinarily contributes to neuronal and or blueberry extracts effectively reversed behavioral shortfalls during aging.” age-related deficits in neuronal and cogni- Tests have since shown that blueberry tive function. In addition, the blueberry- compounds cross the blood-brain barrier fed group far outperformed their peers and localize in rodent brain tissue. while traversing a rotating rod to test balance and coordination. Hard News: Brain Plaques “Despite their status as ‘senior citizens,’ Later, the lab’s researchers published those rats showed remarkable stamina on an Alzheimer’s disease model study in neuromotor function tests,” says psychol- Nutritional Neuroscience. They studied ogist and coauthor Barbara Shukitt-Hale, mice that carried a genetic mutation for also with the Neuroscience Laboratory. promoting increased amounts of amyloid Examination of the brain tissue of those beta, a protein fragment found within the blueberry-fed rats showed much higher telltale neuritic plaque, or “hardening of Biochemist Donna Bielinski prepares mammalian tissue samples to look for the ORAC Units* formation of new neurons , or neurogenesis. (micromole TE/ gram) Selected Vegetables and Nuts the brain,” seen in Alzheimer’s disease. Although the exact cause of Alzheim- 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 er’s is not completely understood, experts have recently identified one mechanism COOKED ARTICHOKE involving the insufficient breakdown (1 cup or 84 grams) and recycling of amyloid protein in the PECANS brain. That mechanism is both genetic (1 ounce or 28.4 grams) and physiological. In those individuals, normally harmless amyloid protein turns WALNUTS (1 ounce or 28.4 grams) into fragments of amyloid beta, which build up as plaque in the brain rather than RAW ASPARAGUS being escorted into cellular recycling. That (3/4 cup or 100 grams) action leads to cell death and weakened RED CABBAGE neuronal communication. (1/2 cup or 75 grams) In the mouse study, beginning at age 4 months—early adulthood—half the brain- RAW SPINACH (8 leaves or 80 grams) plaqued group was fed a diet that included blueberry extract for 8 months. The other WHITE CANNED POTATOES half was fed standard rat chow and so was (1/2 potato or 86.5 grams) a control group of mice that didn’t carry Source: USDA-ARS, Arkansas Children’s Research Center, Little Rock, AR, 2004 data. the amyloid-plaque mutation. At 12 months—early middle age—all *ORAC units include both fat- and water-soluble values. Micromole TE/gram means the groups were tested for their performance number of micromoles of Trolox, a vitamin E equivalent, per 1 gram weight of fresh fruit. in a maze. 10 Agricultural Research/August 2007 424069.indd 10 7/3/07 10:06:40 PM STEPHEN AUSMUS (D832-1) The brain-plaqued mice that were fed the blueberry extract performed as well as the healthy control mice and performed much better than their brain-plaqued peers fed standard chow. A look at the plaqued brains of both the blueberry-fed and chow-fed mice after death revealed no difference in the number of brain plaques in either group. “Amyloid-beta-induced plaques are only one aspect of Alzheimer’s disease,” says Joseph. “But the fact that we saw a diet- induced behavioral difference, despite a similarity in plaque density in both these animal groups, is significant.” The team found increased activity of a family of enzymes called “kinases” in the brains of the amyloid-plaqued mice that were fed blueberry extract. Two kinases found in particular, ERK and PKC, are important in mediating cognitive function, such as converting short-term memory to long-term. “These kinase molecules are involved in signaling pathways for learning and memory,” says Joseph. “It could be that the increased kinase activity within the plaque-ridden brains of the blueberry-fed mice enhanced the signaling in certain receptors.” Brain Cells Are Born ORAC scores of vegetables vary from plant to plant.