"What I tell patients is, if you like coffee, go ahead and drink as much as you want and can," says Dr. Peter Martin, director of the Institute for Coffee Studies at Vanderbilt University. He's even developed a metric for monitoring your dosage: If you are having trouble sleeping, cut back on your last cup of the day. From there, he says, "If you drink that much, it's not going to do you any harm, and it might actually help you. A lot."
Officially, the American Medical Association recommends conservatively that "moderate tea or coffee drinking likely has no negative effect on health, as long as you live an otherwise healthy lifestyle." That is a lackluster endorsement in light of so much recent glowing research. Not only have most of coffee's purported ill effects been disproven—the most recent review fails to link it the development of hypertension—but we have so, so much information about its benefits. We believe they extend from preventing Alzheimer's disease to protecting the liver. What we know goes beyond small-scale studies or limited observations. The past couple of years have seen findings, that, taken together, suggest that we should embrace coffee for reasons beyond the benefits of caffeine, and that we might go so far as to consider it a nutrient.
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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.
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.
"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.
Caffeine might also function as a pain reliever. A study from September suggested as much when its authors stumbled across caffeinated coffee as a possible confounding variable in its study of the back, neck, and shoulder pains plaguing office drones: Those who reported drinking coffee before the experiment experienced less intense pain.
The data is even more intriguing—and more convincing—for caffeine's effects as a salve against more existential pains. While a small study this month found that concentrated amounts of caffeine can increase positivity in the moment, last September the nurses' cohort demonstrated a neat reduction in depression rates among women that became stronger with increased consumption of caffeinated coffee.
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But that caffeine is only mechanism behind coffee's health effects is supported by a small study of 554 Japanese adults from October that looked at coffee and green tea drinking habits in relation to the bundle of risk factors for coronary artery disease, stroke, and type 2 diabetes known together as metabolic syndrome. Only coffee—not tea—was associated with reduced risk, mostly because of dramatic reductions observed in serum triglyceride levels.
So aside from caffeine, just what are you getting in a cup, or two, or six? Thousands of mostly understudied chemicals that contribute to flavor and aroma, including plant phenols, chlorogenic acids, and quinides, all of which function as antioxidants. Diterpenoids in unfiltered coffee may raise good cholesterol and lower bad cholesterol. And, okay, there's also ash which, to be fair, is no more healthful than you would think—though it certainly isn't bad for you.
Some of the chemicals in coffee are known carcinogens, though as far as we know that's only been seen in rodents, not in the small levels we encounter in everyday consumption. Findings, on the other hand, have been supporting that coffee can protect against some cancers. When the Harvard School of Public Health visited the Health Professionals Follow-Up cohort in May 2011, it found that coffee's protective effects extend only to some types of prostate cancer (the most aggressive types, actually). In a separate study of the same population from this past July, they also found a reduced risk of basal cell carcinoma with increased caffeine intake.
The association was strongest for those who drank six or more cups per day.
That same high dosage is also effective in fighting against colorectal cancer, according to a prospective study from June of almost 500,000 adults conducted by the American Society for Nutrition. While the association was greatest for caffeinated varieties, decaf made a small but significant showing. A meta-analysis of 16 independent studies this past January added endometrial cancer to the group of cancers whose relative risk decreases with increased "dosage" of coffee. And in 2011, a large population of post-menopausal women in Sweden saw a "modest" reduction in breast cancer risk with immoderate consumption of 5 or more daily cups.
Taking the benefits of coffee any further requires being patient-specific, but findings apply to a broad range of populations and conditions:
If you have fatty liver disease, a study from last December found that unspecified amounts can reduce your risk of fibrosis.
If you're on a road trip, you may respond like the 24 volunteers for an experiment from February who were subjected to two hours of simulated "monotonous highway driving," given a short break, then sent back out for two more hours. Those given a cup of coffee during the break weaved less, and showed reductions in driving speed, mental effort, and subjective sleepiness. If you're on a weight-training regimen, it can provide a mild (and legal) doping effect.
If you're trying to enhance your workout, the results of one experiment from October found that drinks containing caffeine enhances performance. And then another one from Dr. Martin in 2008: He coauthored a study of people enrolled in Alcoholics Anonymous in which there appeared to be an association between upping coffee intake and staying sober.
Nothing can be all good, and there is still information working against coffee— in October, The Atlantic reported on a study from the health professionals cohort that suggested a link between excessive coffee consumption and glaucoma. "The current recommendation is that if somebody's not drinking coffee, you don't tell them to start," said Bhupathiraju.
But she agrees that drinking coffee, and more of it, does appear to be beneficial. The evidence remains overwhelmingly in coffee's favor. Yes, it was observational, but the study published in May in the New England Journal of Medicine looked at hundreds of thousands of men and women and found this bottom line result: people who drank coffee lived longer than those who didn't.
And the more they drank, the longer they lived. If you're into that sort of thing.