Coffee drinkers are used to being told off. Warnings to drink cups of joe in moderation are all too frequent. The bulk of researchers do — or at least did — think that coffee lovers could seek solace by clinging to one reassuring fact: coffee helps to ward off Type 2 diabetes. Type 2 is usually diagnosed after the age of 35 and in the early stages can be controlled by lifestyle decisions, including diet and exercise.
James Lane of Duke University is one of the leading scientists in a group of researchers who are going against the grind. His research suggests that coffee does more harm than good: “[Coffee] makes Type 2 diabetes worse and could plausibly speed up the development of the disease” says Lane.This is no small claim. Each day over 80 percent of the world’s population consumes caffeine, mainly by enjoying a cup of coffee or tea. In 2007, Type 2 diabetes cost health care organizations more than $174 billion in the United States alone, according to the U.S. Department of Health and Human Services.
Most evidence that coffee is a protective agent against Type 2 diabetes comes from epidemiological studies. In 2007, Balz Frei from Oregon State University published a review of this evidence in Critical Reviews in Food Science and Nutrition. One study included in the analysis followed 14,000 individuals over 12 years in Finland — one of the world’s most coffee-thirsty nations.
The study showed that an individual who drinks seven or more cups of coffee per day is 55 percent less likely to develop Type 2 diabetes than an individual who limits himself to just two cups a day. These associations and percentages are consistent with other epidemiological studies.
Frei found that six out of the nine studies that he reviewed confirmed that heavy coffee consumption is linked to a lower chance of developing diabetes.
But Lane remains skeptical. The review is interesting but “by no means evidence,” he says. Pointing out that correlation does not equal causation, Lane argues that it is therefore premature to imply that coffee prevents diabetes.
For example, Lane says that “Coffee could be a marker for another factor,” and people who drink large amounts of coffee may have something else in common. He suspects that people who drink large amounts of coffee may drink fewer soda drinks, which are more conclusively linked to diabetes.
In a review paper of his own, published last year in the Journal of Caffeine Research, Lane describes a number of experiments by other scientists, which have shown that coffee impedes insulin function. The insulin hormone helps to regulate glucose concentrations in the blood. Individuals develop Type 2 diabetes when insulin function becomes less efficient or fails all together.
According to Lane, there have been at least 17 studies in which researchers gave a dose of caffeine (about 3 cups of coffee worth) and large doses of glucose to subjects via an intravenous drip; the subsequent blood glucose levels were then continuously measured.
These studies showed that caffeine impairs insulin’s ability to regulate the levels of glucose in the blood. They found, on average, a 21 percent rise in blood glucose after dinner due to caffeine consumption.
According to Lane, this proves that a dose of caffeine makes insulin less effective. Lane has proposed two of hypotheses, both of which he believes could be “equally plausible.”
One is that the caffeine wreaks havoc with the hormone adenosine, which is indirectly implicated in insulin’s control over glucose.
The second hypothesis is that caffeine releases stress hormones. These hormones are known to stimulate the production of glucose by the liver.
Preliminary results from a pilot study conducted by Lane show that if Type 2 sufferers abstain from caffeine, their blood glucose levels improve. Although these results are “encouraging, we don’t want to hype it up — it is just a pilot study,” Lane says.
Scientists on the other side of the debate also have holes in their theories. While they maintain that large sample epidemiological studies show that coffee is a friend to those at risk of the disease, they are not yet able to pinpoint exactly which molecule within coffee is beneficial.
Rob van Dam, a researcher from the National University of Singapore, doubts that caffeine is the main beneficial compound since “the association between decaffeinated coffee and risk of Type 2 diabetes is very similar to the association for caffeinated coffee.”
If the beneficial compound in coffee is not caffeine, what is it? According to van Dam, “evidence from animal studies looking for beneficial effects on glucose metabolism is strongest for chlorogenic acid,” an antioxidant. This type of antioxidant is also found in tea by the bucket load, so we would expect to see correlations between heavy tea drinking and low risk of Type 2 diabetes. “There are some studies suggesting that tea consumption is also associated with a lower risk of Type 2 diabetes, but the data are less consistent compared to coffee,” van Dam says.
Despite his research findings, Lane concedes that “caffeine is bad, but other compounds in coffee could well be good — both [sides] might be right.”
So there you have it, clear as mud. Coffee could be bad for your health, or it could be good.
Perhaps we should all switch to decaf? That way you’d get all of the proposed health benefits whilst avoiding the negatives of caffeine. Then again, is caffeine not the point of coffee?