Can caffeine help prevent diabetes?

Better to focus on diet and exercise, than to load up on espresso.

Face it: our society is addicted to caffeine. A guilty pleasure for some and a necessary vice for others, coffee and tea are among the most-consumed beverages in the world. Caffeine, a biologically active ingredient in tea and coffee, is a stimulant with addictive properties that has effects on many parts of our body. Cravings aside, though, is it good for you or bad for you? HealthWatch takes a closer look at a recent study suggesting that high caffeine intake can stave off diabetes.

Tell me about diabetes and its consequences

A brief refresher course: Type 2 diabetes, the kind we're examining here, accounts for 90 per cent of all cases. It occurs when your body becomes resistant to the effects of insulin, which normally controls the level of sugar in your blood.

While asymptomatic in the early phase, its very real consequences can include heart attacks and strokes, numbness and poor circulation, kidney failure, foot ulcers and blindness. Most commonly,

diabetes leads to heart disease that stems from the long-term effects on the coronary arteries that supply blood to the heart; the blockages that develop can lead to heart attacks.

It's important not to underestimate the incidence of this disease. Here in Canada, more than 3 million of us have diabetes, and this number is expected to reach 3.7 million by 2020.

What causes diabetes?

If you're age 40 or over, you're at risk for Type 2 diabetes and should be tested at least every three years. While there is a genetic predisposition to diabetes, obesity is tightly linked, as is one other modifiable risk factor - a sedentary lifestyle. Exercise has been proven to prevent diabetes.

What are the health effects of caffeine?

Caffeine has been given a bad rap by some, partly because of its tendency to give us the jitters and keep us awake at night. That, and a 1981 study showing an association between caffeine and pancreatic cancer, which turned out to be related to the co-consumption of cigarettes, not caffeine.

For most, the amount of caffeine in two to four cups of coffee a day is not harmful. On the positive side, some preliminary research suggests that it has a protective effect against Alzheimer's disease. So possible agitation and sleep disturbance aside, there doesn't seem to be much of a serious downside to caffeine consumption.

The study

Huxley R, Man Ying Lee C, Barzi F et al. Coffee, decaffeinated coffee, and tea consumption in relation to incident Type 2 diabetes mellitus. A systematic review with meta-analysis. Arch Intern Med. 2009;169(22):2053-2063.

How was this research conducted?

This study was a compilation of all of the studies that have ever looked at caffeine consumption and the chances of developing diabetes. A similar study in 2005 that incorporated findings on nearly 200,000 participants reported that drinking six or seven cups of coffee per day reduced a person's risk of developing diabetes by one third. Since 2005, many more relevant studies have been published and this new report adds the numbers from nine new studies for a total of half a million participants.

The individual research projects incorporated into this review were all designed in a similar way and are called cohort studies. In these studies, non-diabetic participants would be followed for a designated period of time: from 3 to 10 years, in the case of this project. They would complete surveys regarding their caffeine consumption, as well as reports on other relevant lifestyle factors. At the end of the study, a small percentage of participants will have begun to show signs of diabetes and the researchers then look back and see whether those who didn't become diabetic happened to consume more caffeine than those who developed the illness.

To what degree can caffeine intake reduce the risk of developing diabetes?

The authors report that each cup of coffee consumed on a daily basis would provide an additional 7-per-cent reduction in the risk of developing diabetes; a similar but weaker effect was noted for tea. The surprising finding was that consumption of decaffeinated coffee also seemed to offer similar benefits, possibly suggesting that other compounds in tea or coffee are responsible for the diabetes-preventing benefits.

Do we believe the results?

Although interesting and seemingly convincing, if one considers the hundreds of thousands of individuals contributing to the study, there are a number of reasons to be skeptical. Chief among these is that while a number of different personal and lifestyle factors were taken into consideration, the reality is that cohort studies can really only say that drinking these beverages is associated with a reduced risk of diabetes, rather than establishing a proven cause-effect connection. It is entirely possible that coffee and tea drinkers are simply more active than most and that's what makes them less likely to become diabetic.

Only a study that compares two very similar groups of study subjects with obligatory consumption and abstinence can determine if there is a causal relationship. Such a study has yet to be done.

So what do we do?

Are you at risk of developing diabetes? You should know the answer based on family history, obesity, dietary habits and whether you lead a sedentary lifestyle. If that's you, don't count on any hot beverage to reduce your chances of developing this chronic disease; the proven answers to prevention are found on the treadmill and on your plate, not in your mug.