Caffeine can cause brief increase in blood pressure

Q Please tell me if coffee, tea and chocolate are bad for a person's heart and high blood pressure. - R.W., Ayden.

A Thanks for your letter. I asked Ricky Bloomfield, an ECU medical student to tell you about the one thing all three foods you mentioned have in common, the stimulant drug caffeine. Here is what Ricky says:

Caffeine is one of the most commonly consumed drugs in the U.S., with an estimated 85 percent of adults consuming some form of caffeine-containing food or drink every day. There has been great debate over the years as to the effects of caffeine on the cardiovascular system (the heart and blood vessels). And so the simple answer to your question is a frustrating, "It depends."

There is much proof that caffeine can raise blood pressure in certain situations, but there is no conclusive evidence that this increase in blood pressure is actually "bad" for you in the long run, except for a special case that will be discussed later.

It has been known since the 1980s that caffeine can raise blood pressure by as much as 10 millimeters (mm) in individuals who do not routinely use caffeinated products. The effects of caffeine on the body can last anywhere from 3-7 hours. Each person responds to caffeine differently, so people drink caffeinated beverages, such as coffee, tea and soda, at different intervals throughout the day to maintain the stimulant effects. Some people find that caffeine helps them think more clearly or stay alert.

It has been also shown that frequent coffee-drinkers can build up a tolerance to the effects of caffeine. In other words, they need to drink 3-6 cups of coffee in order to get the same "buzz" that 1-2 cups used to give them. Studies have shown that for these individuals there is little to no increase in blood pressure when they drink coffee. But, the story doesn't end there.

A study conducted at Duke University several years ago showed that people consuming caffeine in the workplace can actually make work-related stress even worse. It was an interesting study where researchers gave study participants caffeine capsules that were equal to the amount of caffeine in 4 cups of coffee both in the morning and at lunch, and then measured their blood pressure and levels of stress hormones throughout the day. Both measurements remained elevated throughout the afternoon and into the evening.

Regarding those individuals who drink this much caffeine the lead researcher said, "the level of blood-pressure change we saw has been associated with an increased risk of heart disease." He continued by saying that "people consuming typical amounts of coffee and caffeinated soft drinks are probably raising their blood pressure by an amount equal to the beneficial reduction seen with antihypertensive drugs. So if you are taking blood-pressure medication, it may not be doing you any good if you are drinking three or four cups of coffee a day."

It's important to note this study did not prove a link between caffeine and heart disease, only that a relationship between the two may be possible based on the increased blood pressure. Furthermore, the increase in blood pressure caused by caffeine has been shown to be more than 1.5 times worse in patients who already have been diagnosed with high blood pressure, and even greater in the elderly who have hypertension.

So how does caffeine cause an increase in blood pressure in some individuals? It is thought that caffeine acts by causing an increase in adrenaline-type hormones in the body as well as by blocking the effects of adenosine, a hormone that keeps blood vessels open. Both of these effects cause the blood vessels to become narrower, which then increases the pressure inside them. The effect is similar to when the thumb is used to cover the end of a garden hose to cause the water to shoot out at a faster rate. The thumb is essentially narrowing the end of the hose. When the same amount of water attempts to pass through the narrowed opening, the pressure is increased, causing the forceful ejection of water.

Fortunately, the effects of caffeine are not permanent. As these effects wear off, the blood vessels return to their usual, opened state, and blood pressure is returned to normal. That's why your doctor tells you not to use caffeine just before you are having your blood pressure taken.

Besides the effect caffeine has on blood pressure, some experts fear that caffeine may cause problems with the heart's natural rhythm, and cause an arrhythmia or irregular heart beat. This does not seem to happen if caffeine is consumed in moderate amounts but it could be a problem for someone who has a history of heart disease. So doctors often warn people with a history of irregular heart beats to avoid consuming large amounts of caffeine.

Most of the studies about the effect of caffeine on the cardiovascular system have been with coffee drinkers. But caffeine is also found in tea, soda and chocolate. A 5-ounce cup of drip coffee contains about 146 milligrams of caffeine. A regular cola has only about 46 mg. A 5-ounce cup of tea has from 9-46 mg, depending on the type. One ounce of milk chocolate contains about 6 mg of caffeine. So a person would have to eat over 11/2 pounds of milk chocolate to get the same amount of caffeine that is in one cup of drip coffee!

Baking and dark chocolates contain more caffeine at around 35 mg per ounce. Sodas vary a great deal, and unfortunately the caffeine content is not on the label.

So caffeine, a stimulant found in coffee, tea, soda and chocolate, can cause a brief increase in blood pressure (about 10 mm), especially in people not used to it. Talk with your doctor to determine if consuming caffeine is a problem for you. If you want to calculate your caffeine intake, there is a nice "Do It Yourself Caffeine Audit" on the ECU Family Medicine Web site ( www.ecu.edu/fammed [http://www.ecu.edu/fammed] ) under "For Patients," "Patient Education Resources," "Nutrition."

Professor Kathy Kolasa, a registered dietitian and Ph.D., works with the Family Medicine Center, Brody School of Medicine at ECU.