Donald A. Gerber, MD
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Gerber D.; Coffee Consumption and Type 2 Diabetes Mellitus. Ann Intern Med. 2004;141:323. doi: 10.7326/0003-4819-141-4-200408170-00019
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Published: Ann Intern Med. 2004;141(4):323.
TO THE EDITOR:
Salazar-Martinez and colleagues (1) reported that coffee protects against type 2 diabetes mellitus, but their data can also be interpreted to suggest quite the opposite, namely that coffee statistically significantly accelerates the development of diabetes. To illustrate, let us assume that coffee accelerates the development of diabetes in a subgroup of patients but that these patients would probably develop diabetes later in life if they consumed less or no coffee. If this is true, Salazar-Martinez and colleagues, whose study protocol called for excluding persons with known diabetes, would have selectively excluded some participants with coffee-induced early diabetes. Because of this exclusion, fewer participants drinking more coffee would be destined to develop diabetes after study entry than would those drinking less coffee. The modest inverse association between consumption of decaffeinated coffee and risk for diabetes might also be subject to this alternative interpretation, if some of the decaffeinated coffee drinkers were regular coffee drinkers before study entry. The interpretation that coffee accelerates the development of diabetes is more in keeping with the reported short-term metabolic effects of caffeine that Salazar-Martinez and colleagues mentioned. The authors cited a study by van Dam and associates (2) with findings similar to theirs. However, van Dam and associates' study also excluded diabetic persons at entry and is therefore subject to the same alternative interpretation. Excluding diabetes cases that develop in the first 4 years of follow-up, as Salazar-Martinez and colleagues did in one analysis, does not correct for the problem because would-be participants with coffee-induced early diabetes would still be selectively excluded from the heavy coffee drinker group.
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