Two studies published last March in the Journal of the American Medical Association found that heavy coffee drinkers—those typically downing 6 or more cups of the brew per day—face a lower risk of diabetes than persons drinking 2 cups or less. The authors of those studies didn’t pull out the impacts of decaffeinated coffee because too few participants reported drinking it.
These studies might leave the impression that for people with diabetes, or at elevated risk of developing the disease, caffeine is beneficial. However, two new reports indicate the contrary.
James D. Lane and his colleagues at Duke University Medical Center have just released findings that among men and women with type 2 diabetes—the form typically referred to as adult-onset—caffeine ingestion significantly impairs the body’s control of blood sugar and insulin after a meal. In related work, Terry E. Graham of the University of Guelph, Canada, and his co-workers observed the same effect in obese men. Although none of the Canadian volunteers were diabetic, obesity is a leading predisposing risk factor for development of type 2 diabetes.
Globally, some 170 million people suffer from diabetes, a set of three metabolic disorders that impair the body’s effective metabolism of carbohydrates. Most cases are type 2, a life-threatening form that usually develops in adults, especially those who are overweight. In the United States alone, costs for treating diabetes and its medical complications already approach nearly $100 billion annually.
Primarily because of the anticipated graying of the world’s population, diabetes’ incidence is expected to double within the next 3 decades. Sarah Wild of the University of Edinburgh and her colleagues in the May Diabetes Care estimate there will be 366 million people with diabetes by 2030. Given the increasing prevalence of obesity, that could easily prove an underestimate, the team says. Nevertheless, “the ‘diabetes epidemic’ will continue even if levels of obesity remain constant, the group notes. Lowering caffeine intake might prove one way to inexpensively manage aspects of this growing disease.
The new caffeine data dovetail with many earlier, but more limited analyses in recent years. “Even though this research is in its early stages,” Lane told Science News Online, “I think that the effect is sufficiently strong to suggest that people give [decaffeination] a try.” After all, he notes, “it won’t cost them anything—and won’t hurt.”
The drug of choice
Caffeine serves as a primary engine-revving stimulant to jolt the body awake in the morning—and to keep us alert when attention flags mid-day. Although most pharmacological attention has focused on the drug’s role in making the nervous system buzz, other impacts have recently emerged, some of them subtle.
Among these is caffeine’s influence on the body’s hormonal control of energy metabolism. Lane notes that as early as 1967, researchers had observed that caffeine could elevate blood sugar in middle-age diabetics. “No one had looked at it since,” says Lane. “Because probably 80 to 90 percent of adult type 2 diabetics consume caffeine, we thought it was very important to see what effect this drug was having on them.”
So, his team recruited 14 habitual coffee drinkers who didn’t smoke. All had been diagnosed with diabetes at least 6 months earlier but were otherwise healthy.
On two separate mornings after fasting and abstaining from all caffeinated products overnight, the recruits arrived at the Duke medical center lab and received three pills over 60 minutes. On one day, each pill contained 125 milligrams of caffeine—roughly the amount in a typical cup of coffee; on the other day, they contained an inert substance. After downing the third pill, the men and women ate breakfast, a commercially prepared 10-ounce can of what’s marketed as a “meal replacement.” It contained protein, fat, and most importantly for this study, 75 grams of carbohydrates—the amount typically administered in the glucose-tolerance tests used in diabetes screening.
Over the succeeding 2 hours, the researchers drew blood from the volunteers to see how quickly the carbs in their breakfast entered the blood as glucose, a simple sugar, and then disappeared into the body’s cells. Lane’s team also measured blood-insulin concentrations, a gauge of how effectively the cells absorb the insulin that the body dispenses to shepherd glucose.
Blood glucose concentrations remained 21 percent higher among the participants who had taken caffeine pills than when they had received the placebo pills, Lane’s team now reports in the August Diabetes Care. Is that a big deal? “Actually, it is,” the psychologist maintains. The effects of current prescription medications used to control blood-sugar increases after a meal are “the same size as the effect of avoiding caffeine,” Lane observes. His group’s results suggest that “avoiding caffeine could be as important in treatment as these medications are.”
Moreover, Lane’s group observed, blood-insulin concentrations after consumption of the caffeine were 48 percent higher than after the inert pills. This suggests that after caffeine, the cells are even more ignoring insulin—a hallmark of type 2 diabetes.
The scientists administered pure caffeine in these experiments to isolate its effects from those of the hundred or so other chemicals comprising coffee.
Benefits of weight loss, coffee
Graham’s group conducted similar tests in nine sedentary, obese men before and after they embarked on a 12-week diet-and-exercise weight-loss regime. In this case, some of the volunteers received the caffeine challenge, while the rest got inert placebo pills.
During the trial, the men lost, on average, about 8.5 kilograms (18.7 pounds) and almost 3 percent of their body fat. More importantly, the weight loss improved the volunteers’ fasting blood concentrations of sugar and insulin. Their insulin sensitivity in glucose-tolerance testing also increased—unless the men had consumed caffeine. Their insulin sensitivity then appeared no better than before their weight loss. The Guelph group published its findings in the July American Journal of Clinical Nutrition.
Graham points out that the amount of pure caffeine administered was equivalent to about 3 cups of coffee. His group has demonstrated in other studies that coffee possesses compounds—chlorogenic acids—that partially neutralize caffeine’s diabetes-aggravating properties.
Those acids, he points out, are also present in decaf coffee. Other tests by his group indicate that after a meal, blood-sugar concentrations in decaf drinkers are lower than those in people who drank only water (SN: 5/1/04, p. 282: Coffee, Spices, Wine).
Concludes Graham, “If I was a diabetic or had insulin resistance, I would be drinking decaf.”
Lane agrees, noting that people with diabetes have begun asking how they should interpret his data. “I’ve said, ‘We will be doing more studies. You can wait for confirmation of this effect. Or, if you’re a heavy coffee drinker, you can wean yourself off of caffeine and see for yourself whether it improves your blood sugar.'” Indeed, he says, avoiding caffeine “looks like it could have a very dramatic impact on this disease.”