Millions of Americans begin each day with a piping-hot cup of their favorite psycho-stimulating xanthine-alkaloid-containing beverage, coffee. The caffeine in coffee and other beverages elevates the mood, increases alertness, banishes fatigue and heightens athletic ability. Along with such desirable and beneficial effects, caffeine has an undesirable and potentially harmful side effect: increased blood pressure.
Sources
Coffee provides 75 percent of the caffeine consumed in the United States. Coffee-Statistics.com reports that Americans drink 400 million cups of coffee each day. Americans also get their daily dose of caffeine from tea, chocolate, soft drinks, energy drinks, coffee-containing ice cream and chewing gum and over-the-counter drugs.
Mechanism
The pharmacological mechanism caffeine uses to increase alertness and decrease fatigue is the same mechanism by which it raises blood pressure. Caffeine acts by interfering with the function of adenosine in the body. Adenosine is a neurotransmitter. One of its functions is to cause blood vessels to dilate. Normally this results in increased blood flow and lower blood pressure. Chemically, a caffeine molecule closely resembles an adenosine molecule. The resemblance is so close that caffeine can fool the adenosine receptors that control the diameter of blood vessels. While caffeine does not directly act on blood vessels, its interference with adenosine's actions results in blood vessel constriction and elevated blood pressure.
Research
In 1998, Duke University researchers published a study in the journal "Psychosomatic Medicine" that examined the effect of moderate doses of caffeine on adult men and women during a normal work day. The subjects drank an average of 3.5 cups of coffee during work hours. The amount of caffeine ingested from all sources averaged 646 mg per person per work period. The researchers found that caffeine increased systolic blood pressure by 4 mm Hg and diastolic blood pressure by 3 mm Hg.
In 1997, the "Journal of Applied Physiology" published research by the University of California, Davis, that looked at the effects of caffeine on the blood pressure, heart rate and forearm blood flow of male and female cyclists. The study found that caffeine did significantly increase systolic and diastolic blood pressure during resting periods. During periods of exercise, however, caffeine did not appreciably effect the cyclist's blood pressure.
Expert Advice
The National Heart, Lung and Blood Institute (NHLBI) and the American Heart Association (AHA) do not warn against caffeine consumption despite data indicating its hypertensive properties. In a 2004 Editorial Commentary, the AHA said it is "premature" to put caffeine on its list of "perils of daily living." The NHLBI says that caffeine in coffee and other beverages causes only a temporary rise in blood pressure. In a brief article on their website titled "Will Drinking a Lot of Coffee Send Your Blood Pressure Up," they advise readers to continue consuming coffee unless they are sensitive to it or their doctors advise them not to.
References
- National Heart, Lung and Blood Institute : Will Drinking a Lot of Coffee Send Your Blood Pressure Up?
- Hypertension: Editorial Commentaries; Effect of Caffeine on Blood Pressure Beyond the Laboratory
- Coffee-Statistics: Coffee Statistics Report 2011 Edition
- Psychosomatic Medicine: Caffeine raises blood pressure at work
- Circulation: Coffee Acutely Increases Sympathetic Nerve Activity and BP Independently of Caffeine
