Coffee is such a common beverage that you don't often think about whether it may have an impact on health. But the caffeine in coffee is in fact a drug, and in addition, coffee contains hundreds of other compounds that may affect various body functions or diseases. Coffee has been shown to affect two common medical conditions -- diabetes and high blood pressure, or hypertension.
Caffeine and Coffee
When discussing the effects of coffee on health, it is important to distinguish between the effects of caffeine --- which is found in other foods such as tea or chocolate --- and coffee itself, whether with or without caffeine. For example, caffeine affects the way the body responds to insulin. A study reported in the February 2002 issue of "Diabetes Care" showed that in healthy male volunteers, caffeine decreased insulin sensitivity --- the body's response to insulin --- by 15 percent. A similar result was found by researchers who reported in the May 2008 "American Journal of Clinical Nutrition" that caffeinated coffee impaired insulin sensitivity in healthy men but decaffeinated coffee did not. In both studies, the effect was clearly due to caffeine, not necessarily to coffee.
Coffee and Diabetes
According to the Harvard Medical School Family Health Guide, coffee has a protective effect against diabetes. Heavy coffee drinkers are about half as likely to get diabetes as those who drink less. However, decaf coffee improves high density lipoproteins --- HDLs --- which are the blood lipids that protect diabetics from heart disease. Since heart disease is one of the complications of diabetes, the protective effect is important. Regular coffee does not show this protective effect.
Coffee and Hypertension
As far as blood pressure is concerned, the key seems to be how much coffee you drink and whether you continue to drink it over a period of time. Researcher Z. Zhang and colleagues reported in the 2011 March issue of the "American Journal of Clinical Nutrition" that drinking different amounts of coffee increased the risk of hypertension. When coffee consumption increased to 3 cups of coffee a day from 1 cup a day, there was no change in the risk of developing hypertension. But 1 to 3 cups a day did seem to have a slightly elevated risk of hypertension. Yet another report in the March 2002 "Archives of Internal Medicine" concluded that coffee has only a small role in hypertension, even though it does tend to raise the blood pressure slightly over time. But Dr. James Lane, a psychophysiologist at Duke University Medical Center, has been studying caffeine for more than 25 years and has a different viewpoint. He says that caffeine at breakfast and lunch elevates the blood pressure and that it stays elevated until about 10 p.m.
Considerations and Warnings
Neither diabetes nor hypertension are conditions that should be self-managed. If you have questions or concerns about how coffee affects either problem, discuss them with a health-care professional.
References
- "American Journal of Clinical Nutrition"; Caffeinated Coffee Consumption Impairs Blood Glucose Homeostasis in Response to High and Low Glycemic Index Meals in Healthy Men; L.L. Moisey, S. Kacker, A.C. Bickerton, L.E. Robinson, T.E. Graham; May 2008
- "Archives of Internal Medicine"; Coffee Intake and Risk of Hypertension: The Johns Hopkins Precursors Study; Michael J. Klag, MD, MPH, Nae-Yuh Wang, PhD, Lucy A. Meoni, ScM, Frederick L. Brancati, MD, MHS, Lisa A. Cooper, MD, MPH, Kung-Yee Liang, PhD, J. Hunter Young, MD, MHS, Daniel E. Ford, MD, MPH; March 2002
- "American Journal of Clinical Nutrition"; Habitual Coffee Consumption and Risk of Hypertension: A Systematic Review and Meta-analysis of Prospective Observational Studies; Z. Zhang, G. Hu, B. Caballero, L. Appel, L. Chen; March 2011
- Harvard School of Public Health: The Nutrition Source; Ask the Expert: Coffee and Health
- Duke Medicine Health Line: The Real Deal On: Caffeine; March 2010
- "Diabetes Care"; Caffeine Can Decrease Insulin Sensitivity in Humans; G. B. Keijzers, M.D., B.E. De Galan, M.D., C. J. Tack, M.D., P. Smits, M.D.; February 2002
