Caffeine and Blood Pressure

Although caffeine's effects on blood pressure have been widely studied, this research has not produced any widely accepted conclusions. Caffeine may increase blood pressure temporarily, especially in people who are not habitual coffee or caffeinated-beverage drinkers. However, researchers have found no consistent evidence that average caffeine consumption (2-4 cups of brewed coffee per day) increases blood pressure any significant degree for people who do not already have HBP.

The American Heart Association has concluded that there is no harm in the daily consumption of 1-2 cups of coffee or its equivalent.

Case Study 1—Five Groups of Men
In a 2000 study of men, researchers investigated the effects of caffeine consumption on five groups, including:

	Individuals with optimal blood pressure
	Individuals with normal pressure
	Individuals with high normal pressure (prehypertensive)
	Individuals with stage 1 high blood pressure
	Men in treatment for high blood pressure at a hypertension clinic

Their blood pressure was measured after 20 minutes of rest and then again 45-60 minutes after ingesting 250 mg of caffeine, which is equal to about two cups of coffee. (A cup of brewed coffee contains approximately 100 mg of caffeine.)

Findings: Researchers found that caffeine increased blood pressure on average, but not equally in all groups. While there was some increase in both systolic (upper number in a BP reading) and diastolic (lower number in a BP reading) blood pressure for men in the optimal and normal groups, the greatest increases were in the other three groups. In fact, those who were already in treatment for HBP had the highest increases – almost 1.5 times greater than for those with optimal blood pressure. None of the men in the first two categories rose above 140/90 mm Hg (140 mm Hg or above systolic OR 90 mm Hg or above diastolic - the hypertensive range). However, a considerable percentage in the other three categories did reach 140/90 mm Hg. After ingesting caffeine, 19 percent of the high-normal, 15 percent of the stage 1, and 89 percent of the diagnosed hypertensive groups fell into the hypertensive range.

Case Study 2—Men and Women in Their 70s
In a 1999 study of men and women in their 70s, researchers found similar results. Caffeine affected people already diagnosed with HBP the most. Two groups—one with normal blood pressure and one with high blood pressure—were put on a caffeine-free diet for two weeks. Then both groups were divided into sub-groups: one that abstained from caffeine and one that was given caffeine. In the HBP group, systolic blood pressure (top number) rose by 4.8 mm Hg and diastolic blood pressure (bottom number) by 3.0 mm Hg in coffee drinkers over abstainers. There were no significant differences between abstainers and coffee drinkers in the group with normal blood pressure. In older men and women with treated or untreated high blood pressure, blood pressure increased in coffee drinkers and decreased in abstainers.

Findings: The researchers concluded that in older individuals with HBP, restricting coffee intake may be beneficial.

Case Study 3—Women and Caffeine
In a large study of women and caffeine, researchers found that the blood pressure readings of those who consumed little caffeine or a lot of caffeine were unaffected. Interestingly, those who consumed caffeinated colas did have modest increases in blood pressure. The increases were not significant enough that the researchers could recommend not drinking cola.

Findings: There was little difference between those with low and high amounts of caffeine.

Case Study 4—Effects of Energy Drinks
Energy drinks often contain high levels of caffeine. They are only now being studied for their effects on blood pressure.

In one study, healthy young adults drank two energy drinks a day for a week. Their blood pressures were measured five different times over four hours after consuming the energy drinks on the first and last days of the study. In each instance, their blood pressure readings, both systolic and diastolic, were higher after consuming the energy drinks.

Findings: Researchers found that average systolic blood pressure increased by an average of 10 mm Hg and heart rate increased by 5-7 beats per minute over the week.

Until further study, the researchers suggested people with HBP or heart disease should avoid energy drinks because they could affect their blood pressure and may even alter the effectiveness of their medications.

Caffeine can increase heart rate and blood pressure during physical activity. For that reason, consider avoiding caffeine.

This content is reviewed regularly. Last updated 10/19/09.