Time for coffee and tea
Coffee drinking and diabetes
Over the past four years, a number of epidemiological studies have found that consumption of caffeinated and decaffeinated coffee helps lower the risk of diabetes. On the other hand, trials in humans appeared to show a lowered glucose tolerance shortly after taking caffeine or caffeinated coffee — which suggested that coffee consumption might increase the risk of diabetes. What are we to think?
In a review of 20 published epidemiological studies on the relationship between long-term coffee consumption and the risk of diabetes, 17 studies concluded that there was sound evidence that coffee consumption reduced the risk of type-2 diabetes. Only 3 did not find a protective effect, and not one said there was a deleterious effect. Interestingly, four of the 20 studies believed that there were other ingredients, not caffeine, involved in the protective effect.
We know that coffee or caffeine helps individuals to lose weight. This is discussed in a separate article on coffee and weight loss. Knowing this relationship might lead us to suspect that it is the weight loss that causes this protective effect against diabetes. But it is not so. The weight loss effect was actually modest, and it was not enough to explain the ability of caffeine or coffee to reduce diabetes risk.
The effect of coffee on diabetes risk appears to be more closely related to glucose metabolism and insulin sensitivity. You should remember that if your body is insensitive to insulin, it becomes more difficult to deliver glucose to the cells and to burn stored fat to release energy. Increased insulin sensitivity results in less insulin being needed.
Our dilemma above may be resolved by two studies on humans that isolated the effects of caffeinated and decaffeinated coffee. One study found that drinking decaffeinated coffee for 2 weeks decreased the blood glucose levels in healthy volunteers accustomed to taking 560 milligrams (mg) caffeine a day (less than 6 cups). Another study found that volunteers who ingested caffeine showed increased plasma glucose and insulin levels more than that from ground caffeinated coffee, and, that drinking decaffeinated coffee actually resulted in decreased plasma glucose.
The findings in these two studies indicate that some non-caffeine compounds in coffee tend to counteract the impairing action of caffeine on glucose metabolism, and thus contribute to ground coffee’s ability (if consumed regularly) to enhance glucose tolerance and insulin sensitivity. The second study results also suggest that ground decaffeinated coffee has an advantage over ground caffeinated coffee in promoting insulin sensitivity and reducing diabetes risk over the long term.
If it is not caffeine that cuts the risk of diabetes, then there must be some other constituent of coffee that must do it. The various research studies are setting their sights on chlorogenic acids found in coffee, particularly the major type, 5-caffeoxylquinic acid. They took caffeinated and decaffeinated coffee, both containing equal amounts of chlorogenic acid and glucose. They found that chlorogenic acid regulated the rate of glucose uptake.
Research on the short- and long-term effects of decaffeinated coffee and non-caffeine constituents of coffee is still in the early stages. There is early evidence that decaffeinated coffee, some non-caffeine constituents in coffee, or both, may promote glucose tolerance and insulin sensitivity better than caffeinated coffee. But more research is needed to understand the relationship some more.
Diabetes affects approximately 12% of Americans; by year 2010, it is estimated that there will be 220 million cases of type-2 diabetes worldwide. The findings offer some hope that coffee, or some of its constituents, may one day become part of strategies to prevent or treat diabetes.