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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Medical Myths Medical Myths

Coffee -- Grounds for Concern?

October 23, 2012

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Workplace Health
Your Work And Your Life
Coffee -- Grounds for Concern?
Coffee -- Grounds for Concern?
Do you find yourself looking forward to that first cup of coffee in the morning? If drinking coffee is part of your routine, you are not alone. You also have company when it comes to concerns about the health effects of coffee.
Harvard Medical School Commentary

Do you find yourself looking forward to that first cup of coffee in the morning? How about the next cup? If it's part of your routine to drink coffee on a regular basis, you're not alone.

You also have company when it comes to concerns about the health effects of coffee — hundreds of studies have addressed coffee's effect on the body and whether or not caffeine causes harm. Perhaps you've heard it's good to drink coffee when you have a headache, or bad to drink it if you have stomach problems. So what is myth, and what is fact?

Coffee's Punch

The effects of coffee on the body fall into several categories:

    • Stimulant effects. Because one of its major ingredients is caffeine, coffee is a well-established stimulant, meaning that it stimulates the nervous system, including such diverse networks as the nerves controlling intestinal activity, blood pressure and airway size. As a result, any caffeine-containing food or beverage (including tea, cola and chocolate milk) may impair sleep, but avoiding coffee late in the day is usually an easy way to avoid this problem. Jitters and anxiety may also be related to caffeine's stimulant effects.
    • Heartburn. Even decaffeinated coffee can stimulate secretion of stomach acid, leading to heartburn
    • Diuretic features. Caffeine is also a diuretic — it encourages the kidneys to produce urine so effectively that it may contribute to mild dehydration. In addition, the water contained in coffee also leads to frequent urination to rid the body of excess fluid.
    • Miscellaneous. Features of coffee may also have other effects on the body. For example, yellowed teeth are common among regular users of coffee. Injuries related to burns from hot coffee are not rare. And there is even a suggestion by some mental health professionals that occasional caffeine users, including coffee drinkers, should be considered dependent, addicted or struggling with substance abuse.

As for the overall health risks of coffee or caffeine use, concerns have been raised by studies over the past 50 years, including an association with stomach problems, pancreatic and bladder cancer, fibrocystic breast disease and gallbladder disease, among other conditions. When rigorously analyzed, these studies fall far short of implicating modest coffee consumption as a significant health risk, even among pregnant women and cardiac patients. A review from April 2007 examined the evidence that coffee consumption might increase the risk of stomach cancer or leukemia; the data were considered inconclusive and additional study was recommended.

One largely discredited study which found that coffee intake was associated with an increased risk of pancreatic cancer, is often used as a model for how a flawed study design can lead to misleading research results. In that study, researchers analyzed a number of "exposures" among patients with pancreatic cancer, including coffee intake. Because of the number of factors examined, many scientific researchers call this sort of study a "fishing expedition." As reasonable as it may seem to examine many factors at once, the problem is that if you look at enough exposures, one or more will show an association just by chance. So there is a danger of generating misleading results if you cast too wide a net, and well-respected researchers avoid doing so, or they make statistical adjustments to account for analyzing many variables in a single study.

Coffee May Be Good for You

It may surprise you to learn that there are therapeutic uses of caffeine other than as a stimulant to avoid sleep (as in NoDoz, Vivarin and many others):

  • Newborns, especially those who are premature or have undergone surgery just after birth, may be treated with caffeine to stimulate their breathing.
  • Many over-the-counter headache or pain remedies include caffeine (such as Excedrin, which also contains acetaminophen and aspirin). The effectiveness of these agents may be related, at least in part, to the treatment of caffeine withdrawal, a common cause of headaches.
  • Studies have examined whether caffeine could be useful in the treatment of asthma, given its dilating effects on airways, and several have found modest benefits. In fact, some recommend that coffee intake be avoided before breathing tests because the abnormalities that breathing tests aim to detect may be diminished by caffeine intake.
  • Coffee has several effects on the intestinal tract. Although it increases stomach acid and gallbladder contractions, it has not been definitively linked to ulcer disease, it may protect against pain from gallstones and it may even act as a remedy for constipation.
  • A 1999 review (in the medical journal Gut) found a reduced risk of colon cancer among coffee drinkers compared with nonusers, although this association has not been widely accepted and has not led to any specific recommendations to encourage coffee's use.
  • Several studies published in 2003 suggest that coffee reduces the risk of Parkinson's disease. some research suggests that as little as one cup a day can reduce the risk by 50%. Why this may be the case is uncertain, and no clearly beneficial effect of coffee has been demonstrated for people who already have Parkinson's disease.
  • At the American Society for Nutrition's annual conference, Experimental Biology 2007, researchers reviewed evidence that moderate intake of coffee (3 to 5 cups per day) might reduce the risk of diabetes, Alzheimer's disease, kidney stones, gallstones, and depression. Other potentially beneficial effects of coffee included a reduced risk of adenomas of the colon (a precursor of cancer), liver cancer and rectal cancer although the data on these were not conclusive.
  • Recent studies also document a link between coffee consumption and a reduced risk of cirrhosis and gout.

However, contrary to popular belief, coffee is not an effective way to reverse the effects of inebriation.

For the vast majority of coffee drinkers, the news is encouraging: the health risks are minimal if present at all. There are probably rare, high-risk patients who are better off avoiding the stimulant action of caffeine or the heartburn provoked even by decaffeinated coffee.

Perhaps the biggest problem of all for most coffee drinkers is its financial impact. The cost of a cup of coffee can be $3 or more at many specialty coffee shops now. It may be true that the best reasons to drink coffee or to avoid it have little to do with your health.

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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