Yesterday was a good morning to wake up and smell the coffee. The New England Journal of Medicine published outcomes from the the NIH-AARP Diet and Health Study, which found drinking coffee was associated with living longer in both men and women. This is not only the largest study ever to look into this question, NIH-AARP is one of the largest prospective (forward-looking) studies ever performed on nutrition and disease, following more than a half million people for a dozen years.
This follows on the heels of an editorial published last month in the American Journal of Clinical Nutrition entitled "Coffee Consumption and Risk of Chronic Diseases: Changing Our Views," which reviewed the growing evidence that for most people, the benefits of drinking coffee likely outweigh the risks. Though the study published today found no significant relationship between coffee consumption and cancer, a recent analysis of the best studies published to date suggests coffee consumption may lead to a modest reduction in overall cancer incidence. Each daily cup o' joe was associated with about a 3% reduced risk of cancers, especially bladder, breast, mouth, colorectal, endometrial, esophageal, liver, leukemic, pancreatic, and prostate cancers.
One of the reasons it's so difficult to study the relationship between diet and disease is because many dietary behaviors are associated with non-dietary behaviors. For example, people who drink coffee may be more likely to have a cigarette in the other hand, which can lead to spurious conclusions. When these considerations are factored in, though, the best available evidence suggests that coffee consumption is generally health-promoting.
What about the caffeine though? Oh, you mean the substance that, as noted in the journal Nutrition:
1) increases energy availability, 2) increases daily energy expenditure, 3) decreases fatigue, 4) decreases the sense of effort associated with physical activity, 5) enhances physical performance, 6) enhances motor performance, 7) enhances cognitive performance, 8) increases alertness, wakefulness, and feelings of 'energy,' 9) decreases mental fatigue, 10) quickens reactions, 11) increases the accuracy of reactions, 12) increases the ability to concentrate and focus attention, 13) enhances short-term memory, 14) increases the ability to solve problems requiring reasoning, 15) increases the ability to make correct decisions, 16) enhances cognitive functioning capabilities and neuromuscular coordination, and 17) in otherwise healthy non-pregnant adults is safe.
Up to a thousand milligrams of caffeine is considered safe for most people, which translates into about 10 cups of coffee a day. New advice suggests that pregnant women, however, should restrict their caffeine consumption to under just 200 mg a day.
There are a few other coffee caveats. Some health conditions may be worsened by coffee, such as insomnia, anxiety, gastroesophageal reflux (heartburn), high blood pressure, and certain heartbeat rhythm irregularities. There are also compounds in coffee that increase cholesterol levels, but are effectively removed when filtered through paper, so drip coffee is preferable to boiled, French press and espresso.
Despite the growing evidence of health benefits associated with coffee consumption, I still don't recommend my patients drink it -- not because it's not healthy, but because there are even healthier choices. In this way, coffee is like a banana, another common convenient plant product. Just as I encourage people to make healthier fruit choices (apples are better, berries are best), I encourage folks to choose an even healthier beverage, such as green tea or hibiscus.
One final note: not all routes of administering coffee are benign. Consider the title of a case reported last month in the medical literature: "Rectal Perforation... Caused by Rectal Burns Associated With Hot Coffee Enemas."