Food for Thought: Diet and the Aging Brain

Scientists know that certain nutrients and other key chemical compounds are essential to normal brain function in humans. Serious deficiencies in some of these nutrients, such as vitamin B12 and iron, can lead to impaired cognitive function as a result of 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. Can 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 affect the 77 million "baby-boomers" who are now facing retirement. Their independence, quality of life, and even economic status might be defined largely by their ability to "traffic" information signals as they age. In researching the nutrition-brain connection, new technologies are being used! such as modalities 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 its association with brain function is relatively new and evolving.

Scientists at the Agricultural Research Service (A.R.S.) throughout the United States are contributing to a growing body of research that explores the effect of diet and nutrition on the brain and its function across the life span. 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 A.R.S. neuroscientist James Joseph. "Loss of mental agility may be less due to loss of brain cells than to the cells' failure to communicate effectively."

Dr. Joseph heads the Neuroscience Laboratory at the Human Nutrition Research Center on Aging at Tufts University in Boston. There, researchers are looking at the beneficial effects of certain dietary plant compounds to learn how they affect brain function.

He explains: "Vitamins and minerals in plant foods provide protective antioxidants. But fruits, vegetables, nuts, seeds, and grains contain thousands of other types of compounds that contribute significantly to the overall dietary intake of antioxidants. Oxygen Radical Absorbance Capacity (ORAC) is a partial measure of the antioxidant effect; 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."

Perhaps there is no better place in which to gauge the power of antioxidants than between the minute connections of the nerve cells. Many studies in the series are groundbreaking, in that they challenge the long-accepted belief that the central nervous system, which includes the brain, is not capable of regenerating itself!

Other published studies in the series echo similar findings based on human brain research at the Salk Institute in San Diego, California. Using new technologies, Salk scientists disputed the notion that the brain does not make new neurons — a process called neurogenesis — into old age: It does, but at a much slower rate.

One of the first of Dr. Joseph's studies, published in the Journal of Neuroscience, showed a protective effect of consuming antioxidants. Although the exact cause of Alzheimer's disease is not completely understood, experts have recently identified one mechanism involving the insufficient breakdown and recycling of amyloid protein in the brain. That mechanism is both genetic and physiological.

In those individuals, normally harmless amyloid protein turns into fragments of amyloid ? (beta). The fragments build up as plaque in the brain instead of being escorted into cellular recycling. That action leads to cell death and weakened neuronal communication. A newborn sprouts billions of nerve cells while soaking up information from the environment. Lower levels of synapse growth continue in waves throughout the life span. Little-used synapses are eliminated, whereas others are strengthened in a neuronal "pruning" process of sorts.

Neurogenesis also plays a role in the formation of new memories. The capacity of the hippocampus to produce new neurons is thought to be greatly diminished during aging. Neurpns that cannot get their messages through signaling pathways are like cell phones that cannot get their signals through to other cell phones. Why does this happen? As the brain matures, cell division becomes largely restricted to specific regions of the brain, and brain cells tend to become more vulnerable to two partners in crime: oxidative stress and inflammation.

In the body, free radicals — weakened atoms formed during activities of daily living — are missing an electron and want to bond with neighboring biomolecules to stabilize. The problem is that unless free radicals are neutralized, they cause cellular damage (oxidative stress).

Cellular antioxidant defense systems counterbalance these rogue molecules, but. they are not 100 percent effective, particularly as the body and brain mature. The brain is thought to be especially vulnerable to oxidative stress.

Dr. Joseph says: "Weighing just 3 pounds, the brain accounts for only 2 percent of the body's total mass, yet it uses up to half of the body's total oxygen consumed during mental activity." Phytochemicals [plant nutrients], together with essential nutrients in foods, provide a health benefits cocktail of sorts. It is feasible that continued research in this area will point to dietary regimens that are effective in boosting neuronal function. .

Inflammation is thought to be stoked by the overactivation of microglia, the neural immune cells. Microglia are usually dormant, but they migrate to the site of any brain injury. These sentries make up about 20 percent of the cell population in certain regions of the brain.

While seeking to protect and repair tissue, microglia cells produce and send out molecular stress signals, some by way of defensive cytokines, as a "bugle" call to other cells. Those signals begin a cascade of reactions, including the activation of genes that express proteins and other stress chemicals to help clear away cellular debris.

Microglial activation by amyloid ? is thought to be a key event in the progression of Alzheimer's disease. Microglial activation is considered the hallmark of inflammation in the central nervous system. "When microglia are stuck in an always-on loop in response to plaque buildup in the brain, they become problematic in and of themselves," says Dr. Joseph.

In 2007, Francis Lau, a molecular biologist in the Neuroscience Laboratory, published a study that investigated whether blueberry extracts might have a preventive effect on inflammatory signals coming from activated microglia cells. He exposed groups of test cells to various levels of blueberry extracts. He then challenged the cells with oxidative stress by exposing them to a toxin that triggers secretion of inflammatory chemicals.

Neuroinflammation has been linked to the expression of genes that spew two inflammatory enzymes and two cytokines. He found that the blueberry treatment significantly reduced that expression. The blueberry extract also markedly lessened secretion of the two inflammatory cytokines.

(Source: Agricultural Research, August 2007.)

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