Caffeine---that ubiquitous substance found in so many foods, drinks and medicines---is a drug, not a food. And like any drug, it can have both beneficial and harmful effects on the human body. Some research shows that caffeine may affect blood pressure.
About Caffeine
Caffeine, a colorless, bitter substance used for centuries to promote alertness, is found in coffee, tea, chocolate, soft drinks, cocoa, kola nuts and a number of both prescription and over-the-counter medications. According to Drugs.com, each of these can contain varying amounts of caffeine, from a cup of brewed coffee, which can range from 40 to 180mg a cup, to cocoa at 4mg a cup. Chocolate has about 25mg of caffeine per ounce, while a soft drink may contain anywhere from 36 to 90mg an ounce---energy drinks usually contain amounts similar to a cup of coffee. Even decaffeinated coffee has a little caffeine---about 3 to 5mg a cup. Many people drink or eat caffeine-containing substances for the stimulant effect, and may not realize that the caffeine has other health effects.
Caffeine and Blood Pressure
Dr. Sheldon Sheps, writing for the Mayo Clinic's Expert Answers, notes that caffeine can cause a short but dramatic increase in blood pressure. This can happen even if you don't normally have blood pressure problems. Two to three cups of coffee, says Dr. Sheps, can raise both numbers in your blood pressure by up to 13 to 14 mm of mercury, a significant change. The mechanism by which this happens is unclear---it may be from changes in hormones or by stimulating the adrenal glands to release more adrenalin, which raises blood pressure. Coffee, the most common source of caffeine, does increase blood pressure, according to a meta-analysis research study by Z. Zhang et al. published in the March 2011 "American Journal of Clinical Nutrition." These researchers found that one to three cups of coffee a day slightly increased the risk of hypertension. On the other hand, in a report in the April 2011 issue of the "American Journal of Hypertension," researchers found caffeine intake did not consistently affect blood pressure or the risk of hypertension induced by pregnancy. However, a higher caffeine intake in pregnancy did seem to cause an increase in the systolic blood pressure---the top number in a blood pressure reading---during the first and last three months of the pregnancy. At the same time, the researchers found a moderate caffeine intake might actually help protect the heart.
Caffeine Source
It's important to recognize that the source of the caffeine may have an impact on blood pressure. For example, in one study that drew its data from the Nurses' Health Study and was reported in the November 2005 issue of the "Journal of the American Medical Association," researchers found that while coffee did not have an effect on blood pressure, cola drinks---whether sugared or diet---did increase blood pressure. In addition, Dr. Sheps points out that people can develop a tolerance to caffeine, and when they ingest it on a regular basis, there may not be an increase in blood pressure.
The Bottom Line
As of 2011, the evidence on caffeine and blood pressure is mixed. Dr. Sheps suggests that you try checking your blood pressure about 30 minutes after you consume caffeine; if the reading is up by 5 to 10 points, you may have a caffeine sensitivity and could benefit from decreasing or stopping caffeine entirely. Remember that caffeine can cause withdrawal symptoms such as headache, so taper off rather than stopping abruptly. And if you do have high blood pressure, discuss any concerns with your health care professional.
References
- MayoClinic.com; How does caffeine affect blood pressure?; Sheldon G. Sheps, M.D.; November 2009y
- Drugs.com: Caffeine
- "American Journal of Clinical Nutrition"; Habitual Coffee Consumption and Risk of Hypertension: A Systematic Review and Meta-Analysis of Prospective Observational Studies; Z. Zhang, et al.; March 2011
- "American Journal of Hypertension"; Maternal Caffeine Intake, Blood Pressure, and the Risk of Hypertensive Complications During Pregnancy. The Generation R Study.; R. Bakker, et al.; April 2011
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