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Boston, MA - A study examining the long-term relationship between coffee consumption and new-onset diabetes suggests that moderate to high coffee consumption is associated with a significantly lower risk of diabetes. The findings add to a growing body of evidence that, contrary to popular perceptions, coffee may be more healthful than harmful. This includes the possibility that coffee's long-term effects on cardiovascular health may be positive, overwhelming short-term adverse effects on heart rate and blood sugar, authors of the study say.
"The perception has been that if you drink a lot of coffee or have a lot of caffeine, that this is probably bad for you, but there is not much evidence to support this perception," senior study author Dr Frank Hu (Harvard School of Public Health, Boston, MA) told heartwire. "Coffee has been shown in many studies to decrease risk of Parkinson's and gallstone disease and may reduce the risk of colon cancer, but it's only in recent years that people have become aware of this. There has been some suspicion that coffee increases risk of heart disease, because in small studies caffeine was associated with raised cholesterol and homocysteine, and those concerns are legitimate. However, while in short-term studies coffee can increase heart rate and blood sugar, those effects are very transient, and after three or four days, people tend to develop tolerance to these effects."
The study, led by Dr Eduardo Salazar-Martinez (National Institute of Public Health, Cuernavaca, Morelos, Mexico), appears in the January 6, 2004 issue of the Annals of Internal Medicine.1
Long-term coffee consumption in men and women
Hu, Salazar-Martinez, and their coinvestigators used information on coffee consumption from the Health Professionals' Follow-up Study (HPFS) and the Nurses Health Study (NHS). They report that 1333 out of 41 934 men from the HPFS and 4085 out of 84 276 women from the NHS developed diabetes over the course of the follow-up period (12 years and 18 years, respectively). After adjusting for age, body mass index, smoking, physical activity, family history of diabetes, and other risk factors in their analysis, the authors found an inverse association between coffee intakeassessed by questionnaire every two to four yearsand type 2 diabetes. The authors also found a more moderate inverse association between decaffeinated coffee consumption and diabetes, but saw no such association for tea consumption, suggesting that there may be important components in coffee, other than caffeine, that are distinct from compounds in tea and that have protective capacity.
Coffee consumption and diabetes risk|
Coffee consumption |
Multivariate* relative risk in men |
Multivariate* relative risk in women |
|
0 cups | 1.00 | 1.00 |
|
1-3 cups/day | 0.93 | 0.99 |
|
4-5 cups/day | 0.71 | 0.70 |
|
>6 cups/day | 0.46 | 0.71 |
|
p for trend | 0.007 | <0.001 |
The lack of an effect of the potential confounders was one of the most striking findings, Hu emphasized to heartwire. "Usually if you see a protective effect of an exposure, you might assume it must be something good related to this exposure that biased the results toward an inverse association. For coffee, the confounding factors did the opposite, because people who drink a lot of coffee tend to be heavy smokers, they exercise less, and they eat a poor diet, so if these confounding factors were in play, you would expect an increased risk in diabetes with heavy coffee consumption." In fact, the reverse was seen, the authors note, suggesting that coffee may even have had protective effects in people who otherwise had important risk factors for diabetes.
Other smaller studies have shown a similar relationship between coffee consumption and diabetes, but the present study is the first to differentiate between coffee, decaffeinated coffee, and other sources of caffeine. A separate analysis for caffeine intake indicated that a similar relationship was seen between caffeine intake and reduced diabetes risk, suggesting that caffeine contributes to the observed inverse association but does not account for it completely.
Hu points out that it would not be possible to conduct a formal clinical trial of coffee's effects on diabetes and heart-disease risk, making observational studies like his very important. He believes the findings are valid. "There's definitely something going on with coffee," he says, adding that the study results should "open the door" to basic science and clinical investigations to elucidate what components of coffee are beneficial.
Hu himself is not a coffee drinker. "I haven't decided to change my behavior because of this study," he comments, pointing out that in the case of diabetes, clinicians already know what needs to be done to prevent diabetes; there is no need to add coffee consumption to this list. "But for the people who do drink a lot of coffee," says Hu, "this information should tell them that they don't need to worry about it, they don't need to feel guilty."
