Week of May 1, 2004; Vol. 165, No. 18
Coffee, Spices, Wine
New dietary ammo against diabetes?
Janet Raloff, Science News
Non–insulin-dependent diabetes is epidemic in the United States. The potentially deadly disorder afflicts some 16 million people in this country, accounting for 95 percent of all diabetes. The number of people with non–insulin-dependent diabetes is 50 percent greater today than it was just a decade ago. Cardiovascular complications account for half of all deaths among people with this type of diabetes, commonly called type 2, and the disorder is the leading cause of kidney failure, adult blindness, and amputations in the United States. Nationally, medical expenditures associated with treating type 2 diabetes and its complications are about $92 billion per year.
The disease arises when people lose all or part of their sensitivity to insulin, the hormone that normally signals cells to move glucose from the blood into energy-hungry tissues. Because spikes in blood-glucose concentrations can damage the circulatory system and other organs, the long-term health of people with full-blown type 2 diabetes depends upon how tightly they can control their blood sugar concentrations. They do this by making lifestyle changes, such as exercising regularly, losing weight, and choosing certain foods.
People considered to be prediabetic because they have faltering blood sugar control also fare better in the long run if they follow the same lifestyle guidelines.
Restricting intake of sugar and starches is one way that people can maintain moderate blood sugar concentrations. Their diet should include primarily fibrous whole grains that release glucose slowly into the bloodstream (SN: 4/8/00, p. 236: http://www.sciencenews.org/articles/20000408/bob9.asp
). That's a tough challenge in today's fast-food world, dominated by refined, highly processed foods.
However, an assortment of new nutrition data may come as unexpectedly sweet news. Researchers are uncovering mechanisms by which a range of dietary agents—including coffee, wine, and cinnamon—appear to restore some of the body's responsiveness to insulin and control of blood sugar. Such changes seem to be transitory, however, so these foods offer no cure for diabetes. But dietary scientists now suggest that regular intake of these foods might slow the disease's onset and reduce its ravages.
Study after study has shown antidiabetic effects of coffee. The March 10 Journal of the American Medical Association carries the latest epidemiological evidence—two European studies showing that people who drink 6 to 10 cups of coffee, primarily caffeinated, per day tend to develop type 2 diabetes at lower rates than individuals do who drink 2 or fewer cups a day.
For several years, scientists have been asking what constituent of java works to control blood sugar. Gradually, chlorogenic acids, a relatively minor family of chemicals in coffee beans, have emerged as prime candidates.
Much attention focused on caffeine, which has turned out to have a detrimental effect. Terry E. Graham of the University of Guelph in Ontario and his coworkers recently tested the effect of pure caffeine, caffeinated coffee, and decaf on blood sugar in lean and obese people with and without type 2 diabetes. The amount of caffeine in a mug or two of strong coffee was sufficient to disrupt control of blood sugar for several hours in any of those 67 individuals, says Graham. A paper detailing the 56 nondiabetic volunteers is due out soon in the American Journal of Clinical Nutrition.
Giving the volunteers caffeine in plain water followed an hour later by a slug of sugar water induced the highest blood sugar concentrations. The same amount of caffeine delivered in 2 cups of coffee before the sugar jolt raised blood sugar concentrations about 75 percent as much as the pure caffeine did. However, when the researchers gave people two cups of decaffeinated coffee and then the sugar, their blood sugar concentrations were even lower than when they drank plain water before the sugar.
That result suggests that the decaf—and, therefore, some coffee component other than caffeine—has an antidiabetic effect, says Graham.
Last year, Linda M. Morgan and her colleagues at the University of Surrey in England tested nine healthy volunteers. Each made three morning visits to Morgan's lab after fasting overnight. In the lab, they each downed 25 grams of sugar in 2 cups of a beverage. On one morning, they took the sugar in regular coffee; another morning, in decaf; and a third morning, in water. After each sugary drink, they submitted to tests of how much ingested glucose entered their blood during the next 3 hours.
Both coffee types enabled the volunteers to control blood glucose significantly better than they did after drinking the glucose-containing water, the scientists reported in the October 2003 American Journal of Clinical Nutrition. Once in the blood, however, glucose that was drunk with caffeinated coffee tended to stay there, as it would in a person with diabetes. The finding is consistent with other studies showing that caffeine can impair insulin's responsiveness to blood sugar.
By keeping the concentrations of chlorogenic acids the same in the decaf and caffeinated coffees, the researchers made sure that those compounds weren't the source of the effect. Earlier studies by the group had shown that low concentrations of chlorogenic acids naturally present in apples attenuated the release of glucose into the blood after volunteers ate the fruit.
Michael N. Clifford, the research team's food chemist, hypothesizes that chlorogenic acids, which are present in far greater concentrations in coffee than in fruit, reduce the efficiency of molecular-scale pumps that move glucose across the walls of cells lining the digestive tract. These acids would thereby tend to keep sugar in the gut and out of the bloodstream, reducing the chances of the high spikes of blood sugar that exacerbate diabetes.
Jane Shearer of Vanderbilt University in Nashville and her colleagues have studied the effects of pure chlorogenic acids, isolated from decaf, on enzymes that regulate the liver's release of glucose. Ordinarily, between meals, the liver sends glucose into the blood to keep it available to tissues. In people with diabetes, the liver inappropriately sends out glucose even after a meal has already boosted blood concentrations of the sugar.
The researchers showed in rats that chlorogenic acids disrupt the liver enzymes' action, bogging down glucose's release into the blood. This helps prevent blood sugar spikes after meals, the researchers reported in the November 2003 Journal of Nutrition.
A few studies have hinted that teas—with their bounty of antioxidants called polyphenols—might also exhibit antidiabetic properties. In the latest such trial, Lucy S. Hwang of National Taiwan University in Taipei measured green tea's effect on insulin action in rats with experimentally induced diabetes.
Hwang's team substituted room-temperature tea for drinking water for half of the animals. After 12 weeks, tea-drinking rodents exhibited improved insulin sensitivity and lower blood-glucose concentrations during the 2 hours after each meal, the researchers reported in the Feb. 1 Journal of Agricultural and Food Chemistry.
In related test-tube studies, the group measured how well fat cells from these animals absorb glucose, an action that in the body would lower blood sugar concentrations. The cells from diabetic rats drinking green tea absorbed more than twice as much of the sugar as did cells from similar animals drinking plain water—indicating, the researchers say, that the tea had indeed improved the fat cells' insulin sensitivity.
Hwang's group has now tested other types of tea. All true teas are made from leaves from the same species of plant. Green tea is unfermented, whereas black and other teas are fermented to various extents.
Like the green tea in the original test, semifermented pou-chong tea "significantly increased glucose uptake" by fat cells taken from diabetic animals that drank it, Hwang told Science News. However, fully fermented black tea—the favorite of most Western tea drinkers—didn't affect glucose absorption.
Since different teas contain different polyphenols that might underlie the fat-cell response, Hwang's team tested the antidiabetic effects of several polyphenols from the best-performing teas. The most effective turned out to be epigallocatechin gallate, an agent known to have anticancer properties (SN: 7/23/94, p. 61). In her lab tests, the compound has "insulinlike activity," Hwang says.
Hwang's team has traced the green tea's antidiabetic attributes to other mechanisms as well. In rats, green tea increased the number of insulin receptors on cells and the blood concentration of a protein—GLUT-IV—that helps move glucose out of the blood and into cells. Moreover, Hwang notes, the tea activated insulin-receptor kinase, an enzyme that makes the receptors available to bind insulin and initiate activity.
Spice it down
Scientists at the Agriculture Department's Beltsville (Md.) Human Nutrition Research Center have been studying how chromium, which is found in black pepper and some other foods, also boosts the activity of insulin-receptor kinase and related enzymes. Experiments beginning almost a half-century ago showed that chromium supplements can restore blood sugar control to some people and animals with diabetes. The question has been why that is and what might represent effective doses of chromium.
Recent studies have shown that the element chemically alters the cell-surface receptors to which insulin attaches, explains Beltsville chemist Richard A. Anderson. Without chromium, insulin can't dock at the receptors and shepherd glucose from the blood into energy-hungry cells.
When the hormone's job is done, another enzyme switches off the insulin receptor. Chromium also inhibits the shut-off enzyme's action, Anderson says. The element offers dual benefits.
Unfortunately, Anderson observes, the modern diet of highly processed foods is low in chromium. What's more, foods high in sugar stimulate the body to lose chromium.
The formulation of currently available chromium supplements doesn't permit the body to absorb the element efficiently, Anderson says. However, his team has just received a patent for a new formulation, called chromium histidine, that in human trials results in absorption of about 50 percent more chromium than conventional supplements do, he says.
It was during tests of the new chromium supplement that Anderson and his colleagues stumbled onto an entirely different antidiabetes substance in, of all things, apple pie. During the early stages of one study, the researchers were attempting to disrupt some volunteers' blood sugar control by feeding them a low-chromium diet that included pie. Surprisingly, these volunteers' blood sugar remained under control.
Subsequent test-tube studies showed that cinnamon in the pie was boosting insulin activity, as chromium does, and thus controlling blood glucose. The spice turned out to be the "best thing we ever tested" for that purpose, Anderson says.
Anderson and his colleagues recently studied 60 people with type 2 diabetes. The researchers gave the participants capsules containing either cinnamon or wheat flour. The 30 people getting daily doses of 1, 3, or 6 grams of cinnamon for 40 days experienced an 18 to 29 percent drop in blood glucose, compared with their values at the beginning of the study. A gram of cinnamon is about one-half a teaspoon, says Anderson. Volunteers getting wheat flour for 40 days showed no such benefit.
Cinnamon also improved study participants' blood-cholesterol and triglycerides concentrations, Anderson's team reported in the December 2003 Diabetes Care.
Subsequently, the scientists found that cinnamon's active ingredients are polyphenol polymers with insulinlike action. Anderson's team described those experiments in the Jan. 14 Journal of Agricultural and Food Chemistry.
Cloves, bay leaves, and other spices show enzymatic effects similar to those of cinnamon, Anderson has found, though none approaches cinnamon's potency.
If spices and coffee can help control blood sugar, why not wine? After all, studies have suggested that the alcohol and polyphenols that the beverage contains reduce the likelihood of heart complications among people with diabetes (SN: 7/24/99, p. 52). These chemicals might act by increasing cells' insulin sensitivity, reasoned wine biochemist Pierre-Louis Teissèdre of the University of Montpellier in France.
Teissèdre's team separated wine's antioxidant polyphenols from its alcohol. Diabetic mice fed one or the other type of ingredient showed complementary benefits, the scientists reported in the Feb. 15 Journal of Agricultural and Food Chemistry.
For 6 weeks, animals consumed alcohol, polyphenols, both, or neither. The maximum dose was the equivalent, taking body weight into account, of the amount that a person imbibes in three glasses of wine per day. Diabetic animals getting both alcohol and polyphenols controlled their blood sugar after a meal about as well as normal mice did. Mice getting alcohol didn't do quite as well but still had better blood sugar control than did animals getting either the polyphenols only or neither wine ingredient.
The wine components also affected the retarded growth associated with severe diabetes, which prevents cells from accessing the fuel they need to thrive. In Teissèdre's experiment, the mice getting both types of wine ingredients or only alcohol grew larger than did the animals receiving polyphenols only or no wine component.
When receiving both types of wine ingredients, "animals that had been diabetic became nondiabetic," at least temporarily, says Teissèdre. His team envisions developing wines that could be marketed as medicinal beverages—with extra polyphenols for preventing heart disease and fighting diabetes.
It's still too early to know the medical significance of all these tantalizing new findings, observes endocrinologist Nathaniel Clark of the American Diabetes Association in Alexandria, Va. Some may not hold up in long-term dietary tests in people. Even if they do, he notes, it would be "a tragedy" for people to think that supplementing their diets with coffee, tea, spices, or alcohol could take the place of moderate weight loss, regular physical activity, and restricted carbohydrate intake.
Moreover, Clark cautions, certain of these dietary adjustments shouldn't be adopted without advice from a physician. For instance, the caffeine in 6 to 10 cups of coffee—the amount showing an antidiabetes effect in the recent European studies—might prove too much for people with certain heart problems.
And though the diabetes association currently accepts that a daily serving or two of alcohol can fit into the diet of people with the disease, Clark warns that "the risk of overconsumption of alcohol remains, regardless of any potential benefit."
The bottom line, he says, is that people with diabetes should consider any of the potential new menu changes as an addition to existing dietary, weight-control, and exercise strategies—not as a means to avoid them.
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Richard A. Anderson
Nutrient Requirements and Functions Laboratory
Beltsville Human Nutrition Research Center
Building 307, Room 224
Beltsville, MD 20705
Section of Geriatrics
American Diabetes Association
1701 North Beauregard Street
Alexandria, VA 22311
Web site: http://www.diabetes.org/
Michael N. Clifford
Centre for Nutrition and Food Safety
School of Biomedical nd Molecular Sciences
University of Surrey
Guildford, Surrey GU2 7XH
Terry E. Graham
University of Guelph
Human Biology & Nutritional Science
Guelph N1G 2W1
Lucy Sun Hwang
Graduate Institute of Food Science and Techology
National Taiwan University
59, Lane 144, Keelung Road, Sec. 4
Taipei, Taiwan 106
Republic of China
2200 Pierce Avenue
Department of Molecular Physiology and Biophysics
Nashville, TN 37232
Université Montpellier 1
15, Av. Charles Flahault
34093 Montpellier Cedex 5
From Science News, Vol. 165, No. 18, May 1, 2004