Psychology professor Paul E. Gold has researched the stability of glucose levels in the brain. Working with Ewan C. McNay , they found that as rats went through a maze, concentrations of glucose declined in the animals' hippocampus , a key brain area involved in learning and memory – even more dramatically so in older brains.

Except under conditions of starvation, it was thought that the brain always had an ample supply of glucose. "While this is the case in terms of consciousness, the new findings suggest that glucose is not always present in ample amounts to optimally support learning and memory functions," said Gold, who is director of the Medical Scholars Program in the University of Illinois College of Medicine.

"The brain runs on glucose. Young rats can do a pretty good job of supplying all the glucose that a particular area of the brain needs until the task becomes difficult," explained McNay, a postdoctoral researcher in psychology at Yale University. "For an old rat given the same task, the brain glucose supply vanishes out the window. This correlates with a big deficit in performance. A lack of fuel affects the ability to think and remember."

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In the May 2001 issue of Neurobiology of Learning and Memory, Gold, and McNay reported that glucose drainage during a task is specific to the hippocampus, where extracellular levels fell by 30%. (Other brain areas remained stable.) "Only the part of the brain involved with what the animal is asked to do is affected by changes in glucose usage," Gold said.-Not sure how study relates to other study about age, memory and learning.

In the May 2001 issue of the Journal of Gerontology, Gold and McNay described a study which showed how 24-month-old rats experienced a 48% decline in hippocampal extracellular glucose levels, and needed 30 minutes to recover from a maze-related task. Younger, three-month-old rats had only a 12% decline and recovered quickly. When older rats were injected with glucose supplements prior to testing, they did not show the drainage of glucose – and performed at the same levels as the younger rats.

"Glucose enhances learning and memory not only in rats but also in many populations of humans," says Gold. "For schoolchildren, this research implies that the contents and timing of meals may need to be coordinated to have the most beneficial cognitive effects that enhance learning."

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When Dr. Carol Greenwood tested the memory of older adults after they ate a breakfast of mashed potatoes or barley, she found that "eating carbohydrate foods can improve memory within an hour after ingestion in healthy elderly people with relatively poor memories."

In another study, Greenwood and her colleagues at the University of Toronto gave a group of healthy senior citizens a bowl of cereal and milk, along with white grape juice for breakfast. Another group only drank water. When tested twenty minutes later, the cereal-eaters had a better memory – able to remember 25% more facts.

Not only does a diet lacking in carbohydrates cut off the brain's main energy supply, Greenwood said a scarcity of glucose can impede the synthesis of acetylcholine, one of the brain's key neurotransmitters.¹

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Regardless of the source, caloric intake after an overnight fast can cause a short burst in memory capacity, scientists discovered. Carbohydrates, however, generally brought longer-term memory benefits than either fats or proteins in the people tested.

Lead scientist, Dr. Carol Greenwood, emphasized the advantage of nutritious carbohydrates – fruits, vegetables, and whole grains – instead of simple sugars such as pastries. Her studies point to the importance of children's breakfasts to school performance. ²

Another University of Toronto study compared the memory-improving effects of different breakfasts eaten after an overnight fast. Participants who consumed a carbohydrate breakfast of potatoes or barley performed better on short- and long-term memory tests, compared to those who consumed only a glucose-laden lemon drink. Both groups did better than the participants who consumed only an inactive placebo.

"Our study showed that eating carbohydrate foods can improve memory within an hour after ingestion in healthy elderly people with relatively poor memories," said lead author Randall J. Kaplan. "Individuals with seemingly minor deficits in glucose regulation appear to perform worse on cognitive (memory) tests and are most sensitive to the beneficial effects of carbohydrates."³

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Repeatedly overloading the bloodstream with sugar can diminish the body's ability to respond to insulin, and type 2 diabetes may develop.

This is not good for the brain, because diabetes causes a narrowing of the arteries and makes the brain more susceptible to gradual damage. People with diabetes are more vulnerable to depression and are more likely to suffer a decline in mental ability as they age.

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Low blood glucose levels can lead to a significant deterioration in attention abilities, University of Edinburgh researchers concluded after testing healthy individuals in whom hypoglycemia had been induced.

Auditory and visual information was processed more slowly when the subjects' brains were temporarily deprived of its main source of energy. ⁴

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If you've ever had a blood test that measured your fasting blood glucose level, it should be somewhere around 100 milligrams per deciliter. That's one gram of blood sugar per liter of blood, which translates into only about five grams (a teaspoon) of sugar in circulation throughout your entire bloodstream.

Let's say you suck down the typical non-diet soft drink that contains ten times that amount of sugar, which is then quickly absorbed and enters into your bloodstream. Sensors in your brain's hypothalamus will instruct your pancreas to secrete insulin, which causes the cells in your body to pull this overload of glucose out of your bloodstream and store it for later use.

Even when blood sugar levels are again normalized, insulin levels can remain high, because your liver may be unable to remove the circulating insulin fast enough.

In addition, drinking carbonated soft drinks decreases the amount of pure water a person consumes, which can lead to dehydration that depletes the brain and other organs of fluids. (The brain contains a high percentage of water.)

"Currently, soft drinks constitute the leading source of added sugars in the diet, amounting to 36.2 grams daily for adolescent girls and 57.7 grams for boys," according to researchers at the Children's Hospital in Boston. ⁵

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What's more, drinking large quantities of soda can lead to deficiencies in several important vitamins and minerals. A survey of more than 4,000 children, aged 2 to 17 years, found that soda consumption rose 41% between 1989-1995. Soda drinkers were less likely to get the recommended levels of vitamin A or calcium, and were at increased risk of magnesium deficiency. ⁶

Sugar depletes magnesium, and the high levels of phosphoric acid in soft drinks can combine with calcium and magnesium in the gut to cause a loss of these vital minerals.

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In 1998, the Center for Science in the Public Interest (CSPI) published a report titled " Liquid Candy : How Soft Drinks are Harming Americans' Health." A Washington-based nonprofit education and advocacy organization, CSPI focuses on improving the safety and nutritional quality of our food supply. Michael F. Jacobson, Ph.D., writes:

"Teenage girls consume only 60% of the recommended amount of calcium, with soda-pop drinkers consuming almost one-fifth less calcium than non-drinkers. It is crucial for females in their teens and twenties to build up bone mass to reduce the risk of osteoporosis later in life....

"Obesity rates have risen in tandem with soda consumption. Soft drinks provide 10.3% of the calories consumed by overweight teenage boys, but only 7.6% of the calories consumed by other boys. The National Institutes of Health recommends that people trying to lose or control their weight should drink water instead of soft drinks with sugar."

The U.S. Department of Agriculture says that consumption of soft drinks has increased 500% in the last 50 years. During this time, childhood obesity in the U.S. jumped 54% for 6-11 year-olds, and 40% for adolescents.

This boom in childhood obesity could lead in adulthood to a sharp rise in strokes, heart disease, and other vascular-related illnesses. In an ultrasound study of 48 severely obese children, French researchers at the Necker Enfants-Malades Teaching Hospital observed a general decline in function of the lining of the children's arteries, including a loss of vascular elasticity. ⁷

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When for years you repeatedly overload your bloodstream with simple sugars, refined carbohydrates, soft drinks, etc., the swings in blood sugar can take their toll on your body's ability to respond to insulin. Receptors for this hormone may eventually malfunction, becoming "insulin-resistant," so that blood sugar levels remain high – even as your pancreas continues to secrete insulin. Type 2 diabetes can develop.

Nearly 6% of the American population has diabetes. For African Americans, it is 10%. For Native Americans, diabetes increased by 29% between 1990 and 1997 – more than twice the rate for the general U.S. population.

An estimated five million more people have diabetes but don't know it, and nearly 800,000 new cases are diagnosed each year.

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Type 2 diabetes used to be called "adult-onset" diabetes, because it mostly occurred in people over 50. But no longer.

The rising rate of diabetes in children is epidemic. "If you go back 20 years, about 2% of all cases of new onset diabetes (type 2) were in people between 9 and 19 years old. Now, it's about 30% to 50%," says Dr. Gerald Bernstein, an endocrinologist with New York's Beth Israel Medical Center.

Among Americans in their thirties, the 1990s saw a 70% rise in type 2 diabetes, reports the CDC. Other age groups also showed significant increases. For those in their forties the disease rose by 40%, and by 31% for those in their fifties.

A Mayo Clinic study of 11,000 people found that diabetics had a greater decline in cognitive processing speed. "People with either diabetes or strokes are at higher risk not only for cognitive decline but dementia," said Mary Haan, a researcher at University of Michigan School of Public Health. ⁸

In a study of 6,370 patients, ages 55 and older, Dutch researchers at the Erasmus University Medical School found that those with type 2 diabetes faced nearly a 9% increased risk of developing dementia – and Alzheimer's disease in some cases. ⁹

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Over a four-year period, Harvard Medical School researchers tested the memory and mental function of 2,300 women, 70 to 78 years old. Women without diabetes were more than twice as likely to score better than those with diabetes. Also, the longer a woman had diabetes, the more likely she would score poorly on the tests. "Based on calculations within the women in our study, we found that having diabetes was equivalent to aging 4 years in terms of scores," Dr. Francine Grodstein and her colleagues concluded. ¹⁰

In a multiethnic, multicenter study of vascular disease in more than 10,000 people, cognitive test scores were compared six years apart. Diabetes was associated with greater cognitive decline in participants aged 40 to 70 years old, (while high blood pressure was associated with greater cognitive decline only in those older than 58).

"While the participants in the study may not have noticed any decline in their mental ability, the decline was statistically significant," says David Knopman, M.D., a Mayo Clinic neurologist and the senior author of the study. "The results point to the fact that there are things some people may be able to do during middle age to help preserve our mental abilities later in life." ¹¹

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Studies indicate that the presence of both uncontrolled diabetes and hypertension doubles the risk of decreased mental functioning later in life. (Each condition is independently associated with accelerated age-related declines in cognitive functioning.)

"We are talking about hypertension and diabetes as insidious predictors of gradual and subtle decline in cognitive ability," said Merrill Elias, a founding investigator of the Maine-Syracuse Study of Hypertension and Cognitive Function. "Effective treatment or prevention practices can delay or prevent accelerated cognitive decline associated with cardiovascular risk factors." ¹²

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Research presented in June 2001 at the American Diabetes Association's annual meeting showed that high blood glucose levels play a role in the development of atherosclerosis (hardening of the arteries), putting people with diabetes at increased risk for heart disease and stroke.

"Heart attacks and stroke are the major killers of people with diabetes. After following patients with type 1 diabetes for more than 12 years, we can conclude that patients who control their blood glucose significantly lower their risk for worsening atherosclerosis," said David M. Nathan, M.D., co-chairman of the NIH-sponsored study and an investigator at Harvard Medical School.

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When people at high risk for type 2 diabetes exercised at least 30 minutes a day, they reduced their risk by 58%, even without medication. In fact, exercise and diet proved to be nearly twice as effective as a popular diabetes drug.

These were among the findings from the Diabetes Prevention Program announced by the National Institutes of Health in August 2001. This major clinical trial compared diet and exercise to drug treatment in 3,234 people with impaired glucose tolerance, a condition in which blood glucose levels are higher than normal (but not yet diabetic).

Participants maintained their physical activity at 30 minutes per day, usually with walking or other moderate intensity exercise. They also ate a low-fat diet.

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