Editorials
Introducing AFP Journal Club-the Story Behind the Study
See related department on page 1273.
With thousands of medical articles published each year, how do you separate the wheat from the chaff? What is new, true, and clinically important? At American Family Physician, we work to provide readers with "one-stop shopping" for clinical information, whether it is a clinical review article, a Tip from another journal, a Cochrane summary, or a Point-of-Care Guide. In this issue, we introduce a new feature, AFP Journal Club-the Story Behind the Study, which is designed to highlight important clinical studies, as well as help readers become better consumers of the vast medical literature.
This feature is based on the popular Journal Club Live presentations seen by thousands of physicians at medical conventions nationally. We are fortunate to have the originators of Journal Club Live, Drs. Robert Dachs, Mark Graber, and Andrea Darby-Stewart, serve as the presenters of this lively and engaging forum. Each month, the "Three Amigos"-as we like to think of them-will discuss an interesting journal article in a conversational, fun, and interactive manner. These articles will involve a "hot topic" that affects the family physician's practice or that "busts" commonly held medical myths. The authors might tackle a controversy in medicine, or highlight key "practice changers"-studies that prompt you to change how you diagnose or treat a common medical problem.
The format will start with a clinical question, such as "Is one proton pump inhibitor better than another?" The authors will succinctly review what an article says, and then tell us whether we should believe it, and why. They close with advice about what the physician should do, and they provide take-home points for practice.
In sorting through the study, they will also show you how to tell good studies from bad and how to distinguish patient-oriented from disease-oriented evidence, and they will highlight key principles of critical analysis and evidence-based medicine (EBM). They will also demystify statistical concepts and arm readers with tools to make them better judges of what they read. Each discussion will highlight the main clinical points from the articles, as well as the key EBM concepts and statistical terms. We will collect these concepts and terms in our online EBM Toolkit, available at http://www.aafp.org/afp/ebmtoolkit.
We hope this new feature not only provides you with useful clinical information, but also shows you how to do a better job of finding and evaluating important information. We expect that most of our readers will learn from this feature on their own, and we're eager to hear how you like it. Some readers may want to incorporate it into a real-life journal club, and we are interested in hearing how this meets that goal as well. Please send your comments to afpedit@aafp.org.
editor's note: Dr. Siwek is editor of American Family Physician. Dr. Ebell is deputy editor for evidence-based medicine for AFP.
Address correspondence to Jay Siwek, MD, at siwekj@georgetown.edu. Reprints are not available from the authors.
The Safety of Caffeine Consumption
Should family physicians discourage, encourage, or ignore their patients' caffeine intake? After years of investigation and concern over caffeine's adverse effects, there is evidence that caffeine in moderate amounts is not harmful and may have some health benefits.
The most common sources of caffeine for adults are coffee, tea, and sodas. The serving size, the type of product ingested, and the preparation of the product determine the amount of caffeine consumed. An 8-oz serving of drip-brewed coffee contains an average of 85 mg of caffeine, compared with 40 mg in the same amount of brewed tea and 3 mg in decaffeinated coffee. The amount of caffeine in sodas ranges from 24 to 45 mg per 8-oz serving. The Wall Street Journal recently reported large variations in the caffeine content of commercially available coffee (86 to 124 mg per 12 oz).1 Most studies of caffeine are extrapolated from coffee consumption.
The major health concerns about caffeine are whether it is carcinogenic and what effects, if any, it has on the cardiovascular and reproductive systems. Lesser concerns include its potential physiologic and behavioral effects.
Caffeine does not cause or worsen cardiovascular disease.2 It also does not cause serious arrhythmias,3 hypertension,4,5 or coronary artery disease.6 The Joint National Commission for the Detection and Treatment of High Blood Pressure VII does not recommend restricting caffeine consumption to control high blood pressure.
Caffeine is not carcinogenic. It does not increase the risk of colon or breast cancers,7 but the data for stomach, liver, prostate, and lung cancers are limited. Most studies of its effects on bladder and pancreatic cancers found no increased risk8; in the few case-control studies that found an association between caffeine consumption and bladder or pancreatic cancers, the association was weakened when results were adjusted for cigarette smoking.9
Women can drink caffeine safely; it does not increase the risk of fibrocystic breast disease or symptomatic breast discomfort. Although some women may experience delayed conception with caffeine intake greater than 250 mg per day (i.e., the equivalent of three 8-oz cups of brewed coffee), the most detailed prospective study found no association between caffeine consumption and delayed conception.10
Pregnant women are not at greater risk of spontaneous abortion when their caffeine consumption is adjusted for the nausea associated with early pregnancy or when caffeine intake is less than 300 mg per day.11,12 Caffeine does not increase the risk of preterm delivery, genetic abnormalities, or reduction in intellectual functioning.
Caffeine intake is associated with an increase in urinary calcium excretion. However, caffeine intake of less than 400 mg per day has no effect on calcium balance,13,14 and studies that controlled for calcium intake did not find a correlation between caffeine consumption and reduced bone mineral density.15
Because caffeine is a methylxanthine with mild diuretic properties, it is commonly thought that caffeinated beverages are dehydrating. However, normal caffeine intake does not increase the risk of dehydration in athletes or nonathletes.16
Caffeine's effect on human behavior is difficult to determine because of the small size of many studies and numerous variables that can confound the results. Its effect on behavior seems to be the most individually dependent. In general, caffeine increases alertness in situations where arousal is low (e.g., in night-shift workers, in the early morning). Daytime vigilance is also increased. In large amounts, caffeine can increase the time required to fall asleep and reduce sleep duration. However, tolerance to this effect does occur in that regular consumers experience less sleep disturbance.17 Withdrawal symptoms may occur with abrupt discontinuation of caffeine.
What about caffeine's possible health benefits? Coffee drinking is associated with a reduced risk of developing type 2 diabetes, possibly by inducing weight loss. The risk of symptomatic gallstone disease in men, rheumatoid arthritis, alcoholic cirrhosis, and Parkinson's disease is also reduced.
Caffeine intake causes no long-term health consequences in adults and may confer some health benefits. Therefore, moderate caffeine intake is not contraindicated; patients may safely consume two to three cups of coffee or the equivalent amount of caffeine on a daily basis. Family physicians can devote their dietary counseling time to other issues.
Address correspondence to Herbert L. Muncie, Jr., MD, at hmunci@lsuhsc.edu. Reprints are not available from the author.
Author disclosure: Nothing to disclose.
REFERENCES
1. McCarthy MJ. The caffeine count in your morning fix. Wall Street Journal April 13, 2004.
2. Lopez-Garcia E, van Dam RM, Willett WC, Rimm EB, Manson JE, Stampfer MJ, et al. Coffee consumption and coronary heart disease in men and women: a prospective cohort study. Circulation 2006;113:2045-53.
3. Myers MG. Caffeine and cardiac arrhythmias. Ann Intern Med 1991;114:147-50.
4. Klag MJ, Wang NY, Meoni LA, Brancati FL, Cooper LA, Liang KY, et al. Coffee intake and risk of hypertension: the Johns Hopkins Precursors Study. Arch Intern Med 2002;162:657-62.
5. Winkelmayer WC, Stampfer MJ, Willett WC, Curhan GC. Habitual caffeine intake and the risk of hypertension in women. JAMA 2005;294:2330-5.
6. Myers MG, Basinski A. Coffee and coronary heart disease. Arch Intern Med 1992;152:1767-72.
7. Michels KB, Willett WC, Fuchs CS, Giovannucci E. Coffee, tea, and caffeine consumption and incidence of colon and rectal cancer. J Natl Cancer Inst 2005;97:282-92.
8. Viscoli CM, Lachs MS, Horwitz RI. Bladder cancer and coffee drinking: a summary of case-control research. Lancet 1993;341:1432-7.
9. Jain M, Howe GR, St. Louis P, Miller AB. Coffee and alcohol as determinants of risk of pancreas cancer: a case-control study from Toronto. Int J Can 1991;47:384-9.
10. Caan B, Quesenberry CP Jr, Coates AO. Differences in fertility associated with caffeinated beverage consumption. Am J Public Health 1998;88:270-4.
11. Wen W, Shu XO, Jacobs DR Jr, Brown JE. The associations of maternal caffeine consumption and nausea with spontaneous abortion. Epidemiology 2001;12:38-42.
12. Klebanoff MA, Levine RJ, DerSimonian R, Clemens JD, Wilkins DG. Maternal serum paraxanthine, a caffeine metabolite, and the risk of spontaneous abortion. N Engl J Med 1999;341:1639-44.
13. Barger-Lux MJ, Heaney RP, Stegman MR. Effects of moderate caffeine intake on the calcium economy of premenopausal women [Published correction appears in Am J Clin Nutr 1991;53:182]. Am J Clin Nutr 1990;52:722-5.
14. Hasling C, Sondergaard K, Charles P, Mosekilde L. Calcium metabolism in postmenopausal osteoporotic women is determined by dietary calcium and coffee intake. J Nutr 1992;122:1119-26.
15. Lloyd T, Johnson-Rollings N, Eggli DF, Kieselhorst K, Mauger EA, Cusatis DC. Bone status among postmenopausal women with different habitual caffeine intakes: a longitudinal investigation. J Am Coll Nutr 2000;19:256-61.
16. Armstrong LE. Caffeine, body fluid-electrolyte balance, and exercise performance. Int J Sport Nutr Exerc Metab 2002;12:189-206.
17. Nehlig A, Daval JL, Debry G. Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects. Brain Res Brain Res Rev 1992;17:139-70.
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