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In Photos: Coffee for Health ... and Happiness? | Emily Anne Epstein

The most recent findings that support coffee as a panacea will make their premiere this December in the American Journal of Clinical Nutrition. Coffee, researchers found, appears to reduce the risk of type 2 diabetes.

"There have been many metabolic studies that have shown that caffeine, in the short term, increases your blood glucose levels and increases insulin resistance," Shilpa Bhupathiraju, a research fellow at the Harvard School of Public Health's Department of Nutrition and the study's lead author, told me. But "those findings really didn't translate into an increased risk for diabetes long-term." During the over 20 years of follow-up, and controlling for all major lifestyle and dietary risk factors, coffee consumption, regardless of caffeine content, was associated with an 8 percent decrease in the risk of type 2 diabetes in women. In men, the reduction was 4 percent for regular coffee and 7 percent for decaf.

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The findings were arrived at rigorously, relying on data from the Nurses' Health Study and the Health Professionals Follow-Up Study, two prospective studies that followed almost 80,000 women and over 40,000 men from the 1980s through 2008. Although self-reported, the data is believed to be extremely reliable because it comes from individuals who know more about health and disease than the average American (the downside, of course, is that results won't always apply to the general population—but in this case, Bhupathuraju explained that there's no reason to believe that the biological effects seen in health professionals wouldn't be seen in everyone else).

That there were no major differences in risk reduction between regular and decaf coffee suggests there's something in it, aside from its caffeine content, that could be contributing to these observed benefits. It also demonstrates that caffeine was in no way mitigating coffee's therapeutic effects. Of course, what we choose to add to coffee can just as easily negate the benefits—various sugar-sweetened beverages were all significantly associated with an increased risk of diabetes. A learned taste for cream and sugar (made all the more enticing when they're designed to smell like seasonal celebrations) is likely one of the reasons why we associate coffee more with decadence than prudence.

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"Coffee and caffeine have been inexorably intertwined in our thinking, but truth is coffee contains a whole lot of other stuff with biological benefits," said Martin. And most concerns about caffeine's negative effects on the heart have been dispelled. In June, a meta-analysis of ten years of research went so far as to find an inverse association between habitual, moderate consumption and risk of heart failure. The association peaked at four cups per day, and coffee didn't stop being beneficial until subjects had increased their daily consumption to beyond ten cups.