Researchers at Duke University found that drinking five cups of coffee a day could raise blood pressure enough to increase the risk of suffering a heart attack or stroke.
The study is significant because it was conducted while participants were working, in order to determine how caffeine affects people under everyday conditions. Past studies have shown that caffeine elevates blood pressure, but researchers only measured the effects of a single dose of caffeine over a short period of time.
In this study, 19 moderate coffee drinkers (two to five cups per day) wore a blood pressure monitor and checked their pressure every 15 minutes. In the morning, each person was given either 100 or 500 milligrams of caffeine -- dosages equal to one and five cups of coffee. Volunteers kept diaries and, at each blood pressure reading, noted where they were, what they were doing, and how much stress they were under.
The higher dose of caffeine raised blood pressure levels an average of five points. While this increase isn't excessive, most people drink coffee day after day for years -- increasing the risk for stroke and heart disease over time. In other studies, a five-point increase in blood pressure has been associated with a 34 percent increase in the risk of stroke and a 21 percent increase in the incidence of heart disease.
Dr. James Lane, who has been studying caffeine for 15 years and is the lead author of the study, recommends people drink no more than two cups of coffee a day. He also suggests being more thoughtful about why you're reaching for another cup. For example, don't drink coffee because there's just a bit left in the pot or the waiter arrives to give a refill.
Record how much coffee you drink every day for a week. You may be surprised. And remember that tea, many sodas (even orange), and even decaf all add some caffeine to your daily dose.